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Android Development Tutorial
Based on Android 4.0
Lars Vogel
Version 9.8
Copyright © 2009, 2010, 2011, 2012 Lars Vogel
20.02.2012
Revision History
Revision 0.1 04.07.2009
Created
Revision 0.2 - 9.8 07.07.2009 - 20.02.2012
bug fixing and enhancements
Development with Android Gingerbread and Eclipse
This tutorial describes how to create Android applications with Eclipse. It is based on
Eclipse 3.7 (Indigo), Java 1.6 and Android 4.0 (Ice Cream Sandwich).
Table of Contents
1. What is Android?1.1. Android Operation System1.2. Security and permissions
2. Android components2.1. Activity2.2. Views and ViewGroups2.3. Intents
2.4. Services2.5. ContentProvider2.6. BroadcastReceiver2.7. (HomeScreen) Widgets2.8. Other
3. Android Development Tools3.1. What are the Android Development Tools?3.2. Dalvik Virtual Machine3.3. How to develop Android Applications
4. Android Application Architecture4.1. AndroidManifest.xml4.2. R.java and Resources4.3. Assets4.4. Reference to resources in XML files4.5. Activities and Layouts4.6. Activities and Lifecycle4.7. Context
5. Installation5.1. Pre-requisites for using a 64bit Linux5.2. Eclipse and automatic Android SDK5.3. Manually install Android SDK5.4. Install a specific Android version5.5. Android Source Code
6. Android virtual device - Emulator6.1. What is the Android Emulator?6.2. Google vrs. Android AVD6.3. Emulator Shortcuts6.4. Performance6.5. Hardware button
7. Tutorial: Create and run Android Virtual Device8. Error handling and typical problems
8.1. Clean Project8.2. Problems with Android Debug Bridge (adb)8.3. LogCat8.4. Emulator does not start8.5. Error message for @override8.6. Missing Imports8.7. Eclipse Tips
9. Your first Android project9.1. Create Project9.2. Two faces of things9.3. Create attributes9.4. Add UI Elements9.5. Edit UI properties9.6. Code your application9.7. Start Project
10. Starting an deployed application11. Menus and Action Bar
11.1. Definition of menu entries11.2. Action bar tabs11.3. Context menus
12. Tutorial: Menus and Action Bar12.1. Project
12.2. Add a menu XML resource13. Preferences14. Tutorial: Preferences
14.1. Using preferences14.2. Run
15. Layout Manager and ViewGroups15.1. Available Layout Manager15.2. LinearLayout15.3. RelativeLayout15.4. GridLayout
16. ScrollView17. Fragments
17.1. Overview17.2. When to use Fragments
18. Fragments Tutorial18.1. Overview18.2. Create project18.3. Create layouts for landscape mode18.4. Create Fragment classes18.5. Create layouts for landscape mode18.6. Activities18.7. Run
19. DDMS perspective and important views19.1. DDMS - Dalvik Debug Monitor Server19.2. LogCat View19.3. File explorer
20. Shell20.1. Android Debugging Bridge - Shell20.2. Uninstall an application via adb20.3. Emulator Console via telnet
21. Deploy your application on a real device22. Thank you23. Questions and Discussion24. Links and Literature
24.1. Source Code24.2. Android Resources24.3. vogella Resources
1. What is Android?
1.1. Android Operation System
Android is an operating system based on Linux with a Java programming interface.
The Android Software Development Kit (Android SDK) provides all necessary tools to
develop Android applications. This includes a compiler, debugger and a device
emulator, as well as its own virtual machine to run Android programs.
Android is currently primary developed by Google.
Android allows background processing, provides a rich user interface library, supports
2-D and 3-D graphics using the OpenGL libraries, access to the file system and
provides an embedded SQLite database.
Android applications consists out of different components and can re-use components
of other applications if these applications declare their components as available. This
leads to the concept of a task in Android, an application can re-use other Android
components to archive a task.
For example you can write an Application which integrates the a map component and a
camera component to archive a certain task.
1.2. Security and permissions
During deployment on an Android device, the Android system will create a unique user
and group ID for every Android application. Each application file is private to this
generated user, e.g. other applications cannot access these files.
In addition each Android application will be started in its own process.
Therefore by means of the underlying Linux operating system, every Android application
is isolated from other running applications. A misbehaving application cannot easily
harm other Android applications.
If data should be shared the application must do this explicitly, e.g. via a Service or
a ContentProvider.
Android also contains a permission system. Android predefines permissions for certain
tasks but every application can also define its own permissions.
An application must declare in its configuration file (AndroidManifest.xml) that it requires
certain permissions.
Depending on the details of the defined permission, the Android system will during
installation either automatically grant the permission, reject it or ask the user if he grants
these permissions to the application.
If for example the application declares that is requires Internet access then the user
need to confirm this during installation.
This is called "user driven security". The user decides to grant a permission or to deny
it. If the user does not want to give all permissions required by the application, this
application cannot be installed. The check of the permission is only performed during
installation, permissions cannot be denied or granted after the installation.
Typically not all users check the permissions in detail but some users do and if there is
something strange with them, they will write bad reviews on the corresponding Android
markets.
2. Android components
The followings gives a short overview of important Android components.
2.1. Activity
Activity represents the presentation layer of an Android application. A simplified (and
slightly incorrect) description is that an Activity is a a screen. This is slightly incorrect
as Activities can be displayed as dialogs or transparent. An Android application can
have several Activities.
2.2. Views and ViewGroups
Views are user interface widgets, e.g. buttons or text fields. The base class for
all Views isandroid.view.View. Views often have attributes which can be used to change
their appearance and behavior.
A ViewGroup is responsible for arranging other Views e.g. they are layout manager. The
base class for a layout manager is android.view.ViewGroups. ViewGroup also
extends View. ViewGroups can be nestled to create complex layouts. You should not
nestle ViewGroups too deeply as this has a negative impact on performance.
2.3. Intents
Intents are asynchronous messages which allow the application to request functionality
from other components of the Android systen, e.g. from Services or Activities. An
application can call a component directly (explicit intent) or ask the Android system to
evaluate registered components for a certain Intents (implicit intents). For example the
application could implement sharing of data via an Intent and all components which
allow sharing of data would be available for the user to select. Applications register
themselves to an intent via an IntentFilter.Intents allow to combine loosely coupled
components to perform certain tasks.
2.4. Services
Services perform background tasks without providing an UI. They can notify the user
via the notification framework in Android.
2.5. ContentProvider
ContentProvider provides an structured interface to data. Via a ContentProvider your
application can share data with other applications. Android contains an SQLite database
which is frequently used in conjunction with a ContentProvider to persists the data of
the ContentProvider.
2.6. BroadcastReceiver
BroadcastReceiver can be registered to receives system messages
and Intents. BroadcastReceiverwill get notified by the Android system if the specified
situation happens. For example a BroadcastReceivercould get called once the system
completed its boot process or if a phone call is received.
2.7. (HomeScreen) Widgets
Widgets are interactive components which are primary used on the Android
homescreen. They typically display some kind of data and allow the user to perform
actions via them. For example a Widget could display a short summary of new emails
and if the user select a email it could start the email application with the selected email.
2.8. Other
Android provide much more components but the list above describes the most important
ones. Other Android components are "Live Folders" and "Live Wallpapers". Live Folders
display data on the homescreen without launching the corresponding application.
3. Android Development Tools
3.1. What are the Android Development Tools?
Google provides the Android Development Tools (ADT) to develop Android applications
with Eclipse. ADT is a set of plug-in which extended the Eclipse IDE with Android
development capabilities.
ADT contains all required functionality to create, compile, debug and deploy Android
applications from the Eclipse IDE and from the command line. Other IDE's, e.g. IntellJ,
are also reusing components of ADT.
ADT also provides an Android device emulator, so that Android applications can be
tested without a real Android phone.
3.2. Dalvik Virtual Machine
The Android system uses a special virtual machine, i.e. the Dalvik Virtual Machine to
run Java based applications. Dalvik uses special bytecode which is different from Java
bytecode.
Therefore you cannot run standard Java bytecode on Android.
3.3. How to develop Android Applications
Android applications are primary written in the Java programming language. The Java
source files are converted to Java class files by the Java compiler.
Android provides a tool dx which converts Java class files into a dex (Dalvik Executable)
file. All class files of one application are placed in one compressed .dex file. During this
conversion process redundant information in the class files are optimized in the .dex file.
For example if the same String in different class file is found, the .dex file is stored only
once and reference this String in the corresponding classes.
.dex files are therefore much smaller in size then the corresponding class files.
The .dex file and the resources of an Android project, e.g. the images and XML files are
packed into an .apk(Android Package) file. The program aapt (Android Asset Packaging
Tool) perform this packaging.
The resulting .apk file contains all necessary data to run the Android application and can
be deployed to an Android device via the "adb" tool.
The Android Development Tools (ADT) allows that all these steps are performed
transparent to the user; either within Eclipse or via the command line.
If you use the ADT tooling you press a button or run a script and the whole Android
application (.apk file) will be created and deployed.
4. Android Application Architecture
4.1. AndroidManifest.xml
An Android application is described in the file AndroidManifest.xml. This file must
declare all components, e.g. Activities and Services of the application.
It must also contain the required permissions for the application. For example if the
application requires network access it must be specified here.
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="de.vogella.android.temperature"
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".Convert"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<uses-sdk android:minSdkVersion="9" />
</manifest>
The package attribute defines the base package for the following Java elements.
The Android Marketplace requires that very application uses its own unique package.
Therefore it is a good habit to use as package name your reverse domain name. This
will avoid collisions with other developers.
android:versionName and android:versionCode specify the version of your
application. versionNameis what the user sees and can be any string.
versionCode must be an integer. The Android Market determine based
on versionCode if an update of an Android applications on devices is required. You
typically start with "1" and increase this value by one, if you roll-out a new version of
your application.
The tag <activity> defines an Activity, in this example pointing to
thede.vogella.android.temperature.Convert class. An intent filter is registered for this
class which defines that this Activity is started once the application starts
(actionandroid:name="android.intent.action.MAIN" ). The category
definition category android:name="android.intent.category.LAUNCHER" defines that
this application is added to the application directory on the Android device.
The @string/app_name value refer to resource files which contain the actual values.
This makes it easy to provide different resources, e.g. strings, colors, icons, for different
devices and makes it easy to translate applications.
The "uses-sdk" part of the "AndroidManifest.xml" file defines the minimal SDK version
for which your application is valid. This will prevent your application being installed on
devices with older SDK versions.
4.2. R.java and Resources
The " gen " directory in an Android project contains generated values. R.java is a
generated class which contains references to certain resources of the the project.
These resources must be defined in the res directory and can be XML files, icons or
pictures. Via XML files you can for example define values, menus, layouts or
animations.
If you create a new resource, the corresponding reference is automatically created
in R.java. These references are static int values and define ID's for the resources.
The Android system provides methods to access the corresponding resource via these
ID's.
For example to access a String with the reference id R.string.yourString use the
methodgetString(R.string.yourString));.
R.java is automatically created by the Eclipse development environment, manual
changes are not necessary.
4.3. Assets
While the directory res is contains structured values which are known to the Android
platform the directory assetscan be used to store any kind of data. In Java you can
access this data via the AssetsManager and thegetAssets() method .
4.4. Reference to resources in XML files
In your XML files, e.g. your layout files, you can refer to other resources via the @ sign.
For example if you want to refer to a color you defined as resources you can refer to it
via @color/your_id or if you have defined a "hello" string as resource you can access it
via @string/hello .
4.5. Activities and Layouts
The user interface for Activities is defined via layouts. The layout defines the
include Views (widgets) and their properties.
A layout can be defined via Java code or via XML. You typically uses Java code to
generate the layout if you don't know the content until runtime; for example if your layout
depends on content which you read from the Internet.
XML based layouts are defined via a resource file in the folder /res/layout . This file
specifies theViewGroups, Views, their relationship and their attributes for a specific
layout. If a UI element needs to be accessed via Java code you have to give the UI
element an unique id via the android:id attribute. To assign a new id to an UI element
use @+id/yourvalue. By conversion this will create and assign a new id yourvalue to the
corresponding UI element. In your Java code you can later access these UI elements
via the methodfindViewById(R.id.yourvalue).
Defining layouts via XML is usually the preferred way as this separates the
programming logic from the layout definition. It also allows the definition of different
layouts for different devices. You can also mix both approaches.
4.6. Activities and Lifecycle
The operating system controls the life cycle of your application. At any time the Android
system may stop or destroy your application, e.g. because of an incoming call. The
Android system defines a life cycle for activities via pre-defined methods. The most
important methods are:
onSaveInstanceState() - called if the activity is stopped. Used to save data so
that the activity can restore its states if re-started
onPause() - always called if the Activity ends, can be used to release resource or
save data
onResume() - called if the Activity is re-started, can be used to initialize fields
The activity will also be restarted if a so called "configuration change" happens. A
configuration change for example happens if the user changes the orientation of the
device (vertical or horizontal). The activity is in this case restarted to enable the Android
platform to load different resources for these configuration, e.g. layouts for vertical or
horizontal mode. In the emulator you can simulate the change of the orientation
via CNTR+F11.
You can avoid a restart of your application for certain configuration changes via the
configChanges attribute on your activity definition in your AndroidManifest.xml. The
following activity will not be restarted in case of orientation changes or position of the
physical keyboard (hidden / visible).
<activity android:name=".ProgressTestActivity"
android:label="@string/app_name"
android:configChanges="orientation|keyboardHidden|keyboard">
</activity>
4.7. Context
The class android.content.Context provides the connections to the Android system. It
is the interface to global information about the application environment. Context also
provides access to Android Services, e.g. theLocation Service. As Activities and
Services extend the class Context you can directly access the context viathis.
5. Installation
The following assume that you have already Eclipse installed. For details please
see Eclipse Tutorial
5.1. Pre-requisites for using a 64bit Linux
The Android SDK is 32bit, therefore on an 64bit Linux system you need to have the
package ia32-libs installed. For Ubuntu you can do this via the following command.
apt-get install ia32-libs
Please check your distribution documentation if you are using a different flavor of Linux.
5.2. Eclipse and automatic Android SDK
Use the Eclipse update manager to install all available components for the Android
Development Tools (ADT) from the URL https://dl-ssl.google.com/android/eclipse/. If
you are not familiar with the Eclipse update manager the usage is described in Eclipse
update manager.
After the new Android development components are installed you will be prompted to
install the Android SDK. You can use the following wizard or go to the next section to
learn how to do it manually.
5.3. Manually install Android SDK
The previous step downloads the Android SDK automatically for you. You can also
download the Android SDK from the Android SDK download page.
The download contains a zip file which you can extract to any place in your file system,
e.g. I placed it under "c:\android-sdk-windows". Avoid using spaces in the path name
otherwise you may experience problems later.
You also have to define the location of the Android SDK in the Eclipse Preferences. In
Eclipse open the Preferences dialog via Windows → Preferences. Select Android and
enter the installation path of the Android SDK.
5.4. Install a specific Android version
The Android SDK Manager allows you to install specific versions of Android.
Select Window → Android SDK Manager from the Eclipse menu.
The dialog allows you to install new packages and also allows you to delete them.
Select "Available packages" and open the "Third Party Add-ons". Select the Google API
14 (Android 4.0) version of the SDK and press "Install".
Press the "Install" button and confirm the license for all packages. After the installation
completes, restart Eclipse.
5.5. Android Source Code
The following step is optional.
5.5.1. As of Android 4.0
During Android development it is very useful to have the Android source code available
as Android uses a lot of defaults.
As of Android 4.0 the Android development tools provides also the source code. You
can download it via the Android SDK Manager by selecting the "Sources for Android
SDK".
The sources are downloaded to the source directory located in
"path_to_android_sdk/sources/android-xx". xx is the api level number (15 for 4.0.3).
In the Eclipse Package Explorer, right click on your android.jar and
select Properties → Java Source Attachment. Type in the source directory name and
press OK. Afterwards you can browse through the source code.
5.5.2. Prior to Android 4.0
For earlier versions Haris Peco maintains plugins, which provide the Android Source
code code. Use the Eclipse update manager to install the Android Source plugin from
the following update site:
"http://adt-addons.googlecode.com/svn/trunk/source/com.android.ide.eclipse.source.up
date".
More details can be found on the project website.
6. Android virtual device - Emulator
6.1. What is the Android Emulator?
The Android Development Tools (ADT) include an emulator to run an Android system.
The emulator behaves like a real Android device (in most cases) and allows you to test
your application without having a real device.
You can configure the version of the Android system you would like to run, the size of
the SD card, the screen resolution and other relevant settings. You can define several
devices with different configurations.
Via the emulator you select which device should be started, you can also start several in
parallel. These devices are called "Android Virtual Device" (AVD).
The ADT allow to deploy and run your Android program on the AVD.
6.2. Google vrs. Android AVD
During the creation of an AVD you decide if you want an Android device or an Google
device.
An AVD created for Android will contain the programs from the Android Open Source
Project. An AVD created for the Google API's will also contain several Google
applications, most notable the Google Maps application.
If you want to use functionality which is only provided via the Google API's, e.g.
Cloud2DeviceMessaging or Google Maps you must run this application on an AVD with
Google API's.
6.3. Emulator Shortcuts
Obviously you can use the emulator via the keyboard on the right side of the emulator.
But there are also some nice shortcuts which are useful.
Alt+Enter Maximizes the emulator. Nice for demos.
Ctrl+F11 changes the orientation of the emulator.
F8 Turns network on / off.
6.4. Performance
Try to use a smaller resolution for your emulator as for example HVGA. The emulator
gets slower the more pixels its needs to render as it is using software rendering.
Also if you have sufficient memory on your computer, add at least 1 GB of memory to
your emulator. This is the value "Device ram size" during the creation of the AVD.
Also set the flag "Enabled" for Snapshots. This will save the state of the emulator and
let it start much faster.
6.5. Hardware button
Android 4.0 introduced that devices do not have to have hardware button anymore. If
you want to create such an AVD, add the "Hardware Back/Home keys" property to the
device configuration and set it to "false".
7. Tutorial: Create and run Android Virtual Device
To define an Android Virtual Device (ADV) open the "AVD Manager"
via Windows → AVD Manager and press "New".
We can also select the box "Enabled" for Snapshots. This will make the second start of
the virtual device much faster.
At the end press the button "Create AVD". This will create the AVD configuration and
display it under the "Virtual devices".
To test if your setup is correct, select your device and press "Start".
After (a long time) your AVD starts. You are able to use it via the mouse and via the
virtual keyboard of the emulator.
8. Error handling and typical problems
Things are not always working as they should. This section gives an overview over
typical problems and how to solve them.
8.1. Clean Project
Several users report that get the following errors:
1. Project ... is missing required source folder: 'gen'
2. The project could not be built until build path errors are resolved.
3. Unable to open class file R.java.
To solve any of these errors, go to the project menu and select Project → Clean.
8.2. Problems with Android Debug Bridge (adb)
The communication with the emulator or your Android device might have problems. This
communication is handled by the Android Debug Bridge (adb).
Eclipse allows to reset the adb in case this causes problems. Select therefore the
DDMS perspective via Window →Open Perspective → Other → DDMS
To restart the adb, select the "Reset adb" in the Device View.
8.3. LogCat
The "LogCat" View shows you the log messages of your Android device and help you
analyze problems. For example Java exceptions in your program would be shown here.
To open this view, select Window → Show View →Other → Android → LogCat.
8.4. Emulator does not start
If your emulator does not start, make sure that the android-sdk version is in a path
without any spaces in the path name.
8.5. Error message for @override
The @override annotation was introduced in Java 1.6. If you receive an error message
for @override, change the Java compiler level to Java 1.6. To do this right-click on the
project, select Properties → Java Compiler → Compiler compliance level and select
"1.6" in the drop-down box.
8.6. Missing Imports
Java requires that classes which are not part of the standard Java Language be either
fully qualified or declared via imports.
If you see error message with "XX cannot be resolved to a variable", right-click in
your Editor and select Source →Organize Imports to important required packages.
8.7. Eclipse Tips
To work more efficiently with Eclipse,
select Window → Preferences → Java → Editor → Save Actions and select that the
source code should be formatted and that the imports should be organized at every
save.
1. Conventions for the tutorials
Table of Contents
1. API version, package and application name2. Warnings Messages for Strings
1. API version, package and application name
The tutorials of this document have been developed and tested with Android 4.0.3, API
Level 15. Please use this version for all tutorials in this book. Higher version usually
should also work. Lower version of the Android API might also work, but if you face
issues, try the recommended version.
The base package for the projects is always the same as the project name, e.g. if you
are asked to create a project "de.vogella.android.example.test" then the corresponding
package name is "de.vogella.android.example.test".
The Application name, which must be entered on the Android project generation wizard,
will not be predefined. Choose a name you like.
2. Warnings Messages for Strings
The Android development tools are show warnings if you use hard-coded strings, for
example in layout files. While for real application its best practice to use string resource
files we use use Strings directly to simplify the creation of the examples.
9. Your first Android project
9.1. Create Project
This app is also available on the Android Marketplace. Search for "vogella" for find this
example.
Select File → New → Other → Android → Android Project and create the Android
project "de.vogella.android.temperature". Enter the following.
While "res" contains structured values which are known to the Android platform the
directory "assets" can be used to store any kind of data. In Java you can access this
data via the AssetsManager and the method getAssets().
9.2. Two faces of things
The Android SDK allows the developer to define certain artifacts, e.g. strings and UI's,
in two ways: via a rich editor, and directly via XML.
The following description tries to use the rich UI but for validation the resulting XML is
also displayed. You can switch between both things by clicking on the tab on the lower
part of the screen. For example in the Package Explorer select "res/layout/main.xml".
9.3. Create attributes
Android allows you to create attributes for resources, e.g. for strings or colors. These
attributes can be used in your UI definition via XML or in your Java source code.
Select the file "res/values/string.xml" and press "Add". Select "Color" and enter
"myColor" as the name and "#3399CC" as the value.
Add also the following "String" attributes. String attributes allow the developer to
translate the application at a later point.
Table 1. String Attributes
Name Value
celsius to Celsius
fahrenheit to Fahrenheit
calc Calculate
Switch to the XML representation and validate the values.
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello">Hello World, Convert!</string>
<string name="app_name">Temperature Converter</string>
<color name="myColor">#3399CC</color>
<string name="myClickHandler">myClickHandler</string>
<string name="celsius">to Celsius</string>
<string name="fahrenheit">to Fahrenheit</string>
<string name="calc">Calculate</string>
</resources>
9.4. Add UI Elements
Select "res/layout/main.xml" and open the Android editor via a double-click. This editor
allows you to create the UI via drag and drop or via the XML source code. You can
switch between both representations via the tabs at the bottom of the editor. For
changing the position and grouping elements you can use the outline view.
The following shows a screenshot of the Palette view from which you can drag and drop
new UI elements into your layout. Please note that the "Palette" view changes
frequently so your view might be a bit different.
Right-click on the text object “Hello World, Hello!” in the layout. Select Delete on the
popup menu to remove the text object. Then, from the “Palette” view, select Text Fields
and locate “Plain Text”. Drag this onto the layout to create a text input field. All object
types in the section "Text Fields” derive from the class "EditText", they just specify via
an additional attribute which text type can be used.
Now select the Palette section “Form Widgets” and drag a “RadioGroup” object onto the
layout. The number of radio buttons added to the radio button group depends on your
version of Eclipse. Make sure there are two radio buttons by deleting or adding radio
buttons to the group.
From the Palette section Form Widgets, drag a Button object onto the layout.
The result should look like the following.
Switch to "main.xml" and verify that your XML looks like the following.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
<EditText android:layout_height="wrap_content" android:id="@+id/editText1"
android:layout_width="match_parent" android:text="EditText"></EditText>
<RadioGroup android:layout_height="wrap_content" android:id="@+id/radioGroup1"
android:layout_width="match_parent">
<RadioButton android:text="RadioButton"
android:layout_width="wrap_content" android:id="@+id/radio0"
android:layout_height="wrap_content" android:checked="true"></RadioButton>
<RadioButton android:text="RadioButton"
android:layout_width="wrap_content" android:id="@+id/radio1"
android:layout_height="wrap_content"></RadioButton>
</RadioGroup>
<Button android:text="Button" android:id="@+id/button1"
android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
</LinearLayout>
9.5. Edit UI properties
If you select a UI element you can change its properties via the properties view. Most of
the properties can be changed via the right mouse menu. You can also edit properties
of fields directy in XML. Typically you change properties directly in the XML file as this is
much faster. But the right mouse functionality is nice if you are searching for a certain
property.
Open your file "main.xml" We will delete the initial text for the EditText field in XML.
Switch to the XML tab called "main.xml" and delete
the android:text="EditText" property from the EditText part. Switch back to the
"Graphical Layout" tab and check that the text is removed.
Use the right mouse click on the first radio button to assign the "celsius" string attribute
to its "text" property. Assign the and "fahrenheit" string attribute to the second radio
button.
From now on I assume you are able to use the properties menu on the UI elements.
You can either edit the XML file or modify the properties via right mouse click.
Set the property "Checked" to true for the first RadioButton. Assign "calc" to the text
property of your button and assign "myClickHandler" to the "onClick" property. Set the
"Input type" property to "numberSigned" and "numberDecimal" on your EditText.
All your other UI controls are contained in a LinearLayout. We want to assign a
background color to this LinearLayout. Right-click on an empty space in Graphical
Layout mode, then select Other Properties → All by Name→ Background. Select
“Color” and then “myColor” in the list.
Switch to the "main.xml" tab and verify that the XML is correctly maintained.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent" android:background="@color/myColor">
<EditText android:layout_height="wrap_content" android:id="@+id/editText1"
android:layout_width="match_parent" android:inputType="numberDecimal|numberSigned"></EditText>
<RadioGroup android:layout_height="wrap_content" android:id="@+id/radioGroup1"
android:layout_width="match_parent">
<RadioButton android:layout_width="wrap_content"
android:id="@+id/radio0" android:layout_height="wrap_content"
android:text="@string/celsius" android:checked="true"></RadioButton>
<RadioButton android:layout_width="wrap_content"
android:id="@+id/radio1" android:layout_height="wrap_content"
android:text="@string/fahrenheit"></RadioButton>
</RadioGroup>
<Button android:id="@+id/button1" android:layout_width="wrap_content"
android:layout_height="wrap_content" android:text="@string/calc"
android:onClick="myClickHandler"></Button>
</LinearLayout>
9.6. Code your application
During the generation of your new Android project you specified that
an Activity called ConvertActivityshould get created. The project wizard also created
the corresponding Java classs.
Change your code in ConvertActivity.java to the following. Note that
the myClickHandler will be called based on the OnClick property of your button.
package de.vogella.android.temperature;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.Toast;
public class ConvertActivity extends Activity {
private EditText text;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
text = (EditText) findViewById(R.id.editText1);
}
// This method is called at button click because we assigned the name to the
// "On Click property" of the button
public void myClickHandler(View view) {
switch (view.getId()) {
case R.id.button1:
RadioButton celsiusButton = (RadioButton) findViewById(R.id.radio0);
RadioButton fahrenheitButton = (RadioButton) findViewById(R.id.radio1);
if (text.getText().length() == 0) {
Toast.makeText(this, "Please enter a valid number",
Toast.LENGTH_LONG).show();
return;
}
float inputValue = Float.parseFloat(text.getText().toString());
if (celsiusButton.isChecked()) {
text.setText(String
.valueOf(convertFahrenheitToCelsius(inputValue)));
celsiusButton.setChecked(false);
fahrenheitButton.setChecked(true);
} else {
text.setText(String
.valueOf(convertCelsiusToFahrenheit(inputValue)));
fahrenheitButton.setChecked(false);
celsiusButton.setChecked(true);
}
break;
}
}
// Converts to celsius
private float convertFahrenheitToCelsius(float fahrenheit) {
return ((fahrenheit - 32) * 5 / 9);
}
// Converts to fahrenheit
private float convertCelsiusToFahrenheit(float celsius) {
return ((celsius * 9) / 5) + 32;
}
}
9.7. Start Project
To start the Android Application, select your project, right click on it, and select Run-
As → Android Application. Be patient, the emulator starts up very slowly.
You should get the following result.
Type in a number, select your conversion and press the button. The result should be
displayed and the other option should get selected.
10. Starting an deployed application
After you run your application on the virtual device you can start it again on the device.
If you press the Home button you can also select your application.
11. Menus and Action Bar
11.1. Definition of menu entries
Android provides two possible ways to display global actions which the user can select.
The first one is the usage of the Action Bar in the application. The Action Bar is a
window feature at the top of the activity that may display the activity title, navigation
modes, and other interactive items.
The second option is that the app can open a menu which shows additional actions via
a popup menu. Typically you define your menu entries in a way that they are added to
the action bar if sufficient space is available in the action bar and if not, remaining menu
items are displayed in the popup menu.
The option menu and the action bar of your activity is filled by the method
onCreateOptionsMenu() of your activity.
The ActionBar also shows an icon of your application. You can also add an action to
this icon. If you select this icon the onOptionsItemSelected() method will be called with
the value android.R.id.home. The recommendation is to return to the main Activity in
your program.
// If home icon is clicked return to main Activity
case android.R.id.home:
Intent intent = new Intent(this, OverviewActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
break;
In this method you can create the menu programmatically or you can use a pre-defined
XML resources which you inflate via the MenuInflator class. Each Activity has
already an instance of the class available and this instance can get accessed via
the getMenuInflator() method.
The onCreateOptionsMenu() method is only called once. If you want to influence the
menu later you have to use the onPrepareOptionsMenu() method.
11.2. Action bar tabs
It is also possible to add tabs to an action bar.
11.3. Context menus
You can also assign a context menu to an UI widget (view). A context menu is activated
if the user "long presses" the view.
A context menu for a view is registered via the registerForContextMenu(view) method.
TheonCreateContextMenu() method is called every time a context menu is activated as
the context menu is discarded after its usage. The Android platform may also add
options to your View, e.g. EditText provides context options to select text, etc.
12. Tutorial: Menus and Action Bar
12.1. Project
This chapter will demonstrate how to create and evaluate a option menu which is
displayed in the action bar if sufficient space is available. This example will be extended
in the chapter about preferences.
Create a project called "de.vogella.android.socialapp" with the Activity called
"OverviewActivity". Change the "main.xml" layout file in the diretory "/res/layout/" to the
following:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<Button
android:id="@+id/Button01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Show Preferences" >
</Button>
<Button
android:id="@+id/Button02"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Change Preferences" >
</Button>
</LinearLayout>
12.2. Add a menu XML resource
Select your project, right click on it and select New → Other → Android → Android XML
File to create a new XML resource.
Select the option "Menu", enter as File "mainmenu.xml" and press the button "Finish".
This will create a new file "mainmenu.xml" in the folder "res/menu" of your project.
Android provides a nice editor to edit this file, unfortunately this editor is not always
automatically used due to bugs in the ADT. If that happens, you can open this editor
manually. Right-click on your menu file and select Open with → Android Menu Editor.
Switch if necessary to the "Layout" tab of the editor. Press Add and select "Item".
Maintain the following value. This defines the entries in your menu. We will also define
that the menu entry is displayed in the action bar if there is sufficient space available.
Change your Activity class "OverviewActivity" to the following. The
OnCreateOptionsMenu method is used to create the menu. The behavior in
"onOptionsItemSelected" is currently hard-coded to show a Toast and will soon call the
preference settings. In case you want to disable or hide menu items you can use the
method "onPrepareOptionsMenu" which is called every time the menu is called.
package de.vogella.android.socialapp;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;
public class OverviewActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.mainmenu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
Toast.makeText(this, "Just a test", Toast.LENGTH_SHORT).show();
return true;
}
}
Run your application. As there is enough space in the action bar your item will be
displayed there. If there would be more items you could press "Menu" on the emulator
to see them. If you select the menu item you should see a small info message.
The two "Preference" buttons are not yet active. We will use them in the next chapter.
13. Preferences
Android supports the usage of Preferences to allow you to save data for your
application. Preferences are stored as key values. The definition of Preferences can
also be done via an XML resource.
Android provides the class "PreferenceActivity" which extends the class Activity.
PreferenceActivity supports the simple handling of preferences. This activity can load a
preference definition resources via the method addPreferencesFromResource().
To communicate between different components Android uses Intents. Typically the
PreferenceActivity is started from another activity via an Intent.
In your application you can access the preference manager via the following:
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
Values can get access via the key of the preference setting.
String username = preferences.getString("username", "n/a");
To create or change preferences you have to call the edit() methods. Once you have
changed the value you have to call commit() to apply your changes.
Editor edit = preferences.edit();
edit.putString("username", "new_value_for_user");
edit.commit();
14. Tutorial: Preferences
14.1. Using preferences
We will continue using the example project "de.vogella.android.social".
Create an Android XML resource "preferences.xml" of type "PreferenceScreen".
Open the file via right-mouse click and Open-with → Android XML Resource Editor.
Press Add, add a "PreferenceCategory" and add two preferences "EditTextPreferences"
to this category : "User" and "Password".
You can also enter values for other properties of EditTextField, e.g. the inputMethod.
Add the following attribute to the XML definition of your password field to make the input
quoted with *.
android:inputType="textPassword"
Create the class MyPreferencesActivity which extends PreferenceActivity.
This Activity will load the "preference.xml" file and will allow the user to change the
values.
package de.vogella.android.socialapp;
import android.os.Bundle;
import android.preference.PreferenceActivity;
public class MyPreferencesActivity extends PreferenceActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
}
}
To make this class available as an activity for Android you need to register it in your
"AndroidManifest.xml" file. Select "AndroidManifest.xml" and the tab "Application". Scroll
to the botton of the view and add your new activity via the "Add" button.
To make use of our new preference activity and the preference values we adjust the
"OverviewActivity". The first button will show the current values of the preferences via a
Toast and the second button will revert the maintained user name to demonstrate how
you could change the preferences via code.
package de.vogella.android.socialapp;
import android.app.Activity;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;
public class OverviewActivity extends Activity {
SharedPreferences preferences;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button button = (Button) findViewById(R.id.Button01);
// Initialize preferences
preferences = PreferenceManager.getDefaultSharedPreferences(this);
button.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
String username = preferences.getString("username", "n/a");
String password = preferences.getString("password", "n/a");
showPrefs(username, password);
}
});
Button buttonChangePreferences = (Button) findViewById(R.id.Button02);
buttonChangePreferences.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
updatePreferenceValue();
}
});
}
private void showPrefs(String username, String password){
Toast.makeText(
OverviewActivity.this,
"Input: " + username + " and password: "
+ password, Toast.LENGTH_LONG).show();
}
private void updatePreferenceValue(){
Editor edit = preferences.edit();
String username = preferences.getString("username", "n/a");
// We will just revert the current user name and save again
StringBuffer buffer = new StringBuffer();
for (int i = username.length() - 1; i >= 0; i--) {
buffer.append(username.charAt(i));
}
edit.putString("username", buffer.toString());
edit.commit();
// A toast is a view containing a quick little message for the
// user. We give a little feedback
Toast.makeText(OverviewActivity.this,
"Reverted string sequence of user name.",
Toast.LENGTH_LONG).show();
}
To open the new preference Activity we will use
the onOptionsItemSelected() method. Even though we currently have only one option
in our menu we use a switch to be ready for several new menu entries. To see the
current values of the preferences we define a button and use the
class PreferenceManager to get the sharedPreferences.
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.mainmenu, menu);
return true;
}
// This method is called once the menu is selected
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
// We have only one menu option
case R.id.preferences:
// Launch Preference activity
Intent i = new Intent(OverviewActivity.this, MyPreferencesActivity.class);
startActivity(i);
// Some feedback to the user
Toast.makeText(OverviewActivity.this, "Enter your user credentials.",
Toast.LENGTH_LONG).show();
break;
}
return true;
}
14.2. Run
Run your application. Press the "menu" hardware button and then select your menu
item "Preferences". You should be able to enter your user settings then press the back
hardware button to return to your main activity. The saved values should be displayed in
a small message windows (Toast) if you press your first button. If you press the second
button the username should be reversed.
15. Layout Manager and ViewGroups
15.1. Available Layout Manager
A layout manager is a subclass of ViewGroup and is responsible for the layout of itself
and its child Views. Android supports different default layout managers.
As of Android 4.0 the most relevant layout manager
are LinearLayout, FrameLayout, RelativeLayout andGridLayout.
All layouts allow the developer to define attributes. Children can also define attributes
which may be evaluated by their parent layout.
AbsoluteLayoutLayout is deprecated and TableLayout can be implemented more
effectively viaGridLayout
15.2. LinearLayout
LinearLayout puts all its child elements into a single column or row depending on
the android:orientationattribute. Possible values for this attribute
are horizontal and vertical, horizontal is the default value.
LinearLayout can be nested to achieve more complex layouts.
15.3. RelativeLayout
RelativeLayout allow to position the widget relative to each other. This allows for
complex layouts.
A simple usage for RelativeLayout is if you want to center a single component. Just
add one component to theRelativeLayout and set
the android:layout_centerInParent attribute to true.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ProgressBar
android:id="@+id/progressBar1"
style="?android:attr/progressBarStyleLarge"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
/>
</RelativeLayout>
15.4. GridLayout
15.4.1. Overview
GridLayout was introduced with Android 4.0. This layout allows you to organize a view
into a Grid. GridLayout separates its drawing area into: rows, columns, and cells.
You can specify how many columns you want for define for each View in which row and
column it should be placed and how many columns and rows it should use. If not
specified GridLayout uses defaults, e.g. one column, one row and the position of
a View depends on the order of the declaration of the Views.
15.4.2. Tutorial GridLayout
Create the project "de.vogella.android.layout.gridlayout" with the Activity called
"DemoGridLayout".
Change "main.xml" to the following.
<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/GridLayout1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:columnCount="4"
android:useDefaultMargins="true" >
<TextView
android:layout_column="0"
android:layout_columnSpan="3"
android:layout_gravity="center_horizontal"
android:layout_marginTop="40dp"
android:layout_row="0"
android:text="User Credentials"
android:textSize="32dip" />
<TextView
android:layout_column="0"
android:layout_gravity="right"
android:layout_row="1"
android:text="User Name: " >
</TextView>
<EditText
android:id="@+id/input1"
android:layout_column="1"
android:layout_columnSpan="2"
android:layout_row="1"
android:ems="10" />
<TextView
android:layout_column="0"
android:layout_gravity="right"
android:layout_row="2"
android:text="Password: " >
</TextView>
<EditText
android:id="@+id/input1"
android:layout_column="1"
android:layout_columnSpan="2"
android:layout_row="2"
android:ems="8" />
<Button
android:id="@+id/button1"
android:layout_column="2"
android:layout_row="3"
android:text="Login" />
</GridLayout>
Run your example. You should see a nice arranged layout.
This is a layout example wherefore we have not connected any functionality to it. To
extend this example you could now connect the Button with a method in
the Activity via its android:onClick.
16. ScrollView
ScrollViews can be used to contain one view that might be to big to fit on one screen. If
the view is to big the ScrollView will display a scroll bar to scroll the context. Of course
this view can be a layout which can then contain other elements.
Create an android project "de.vogella.android.scrollview" with the activity "ScrollView".
Create the following layout and class.
<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:fillViewport="true"
android:orientation="vertical" >
<LinearLayout
android:id="@+id/LinearLayout01"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="@+id/TextView01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:paddingLeft="8dip"
android:paddingRight="8dip"
android:paddingTop="8dip"
android:text="This is a header"
android:textAppearance="?android:attr/textAppearanceLarge" >
</TextView>
<TextView
android:id="@+id/TextView02"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:layout_weight="1.0"
android:text="@+id/TextView02" >
</TextView>
<LinearLayout
android:id="@+id/LinearLayout02"
android:layout_width="wrap_content"
android:layout_height="wrap_content" >
<Button
android:id="@+id/Button01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:text="Submit" >
</Button>
<Button
android:id="@+id/Button02"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:text="Cancel" >
</Button>
</LinearLayout>
</LinearLayout>
</ScrollView>
package de.vogella.android.scrollview;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class ScrollView extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TextView view = (TextView) findViewById(R.id.TextView02);
String s="";
for (int i=0; i < 100; i++) {
s += "vogella.de ";
}
view.setText(s);
}
}
The attribute "android:fillViewport="true"" ensures that the scrollview is set to the full
screen even if the elements are smaller then one screen and the "layout_weight" tell the
android system that these elements should be extended.
17. Fragments
17.1. Overview
Fragment components allow you to organize your application code so that it is easier to
support different sized devices.
Fragments are components with their own lifecycle and their own user interface. They
can be defined via layout files or via coding.
Fragments always run in the context of an Activity. If an Activity is stopped
its Fragments will also be stopped; if an Activity is destroyed its Fragments will also get
destroyed.
If a Fragment component is defined in an XML layout file, the android:name attribute
points to the Fragmentsclass.
The base class for Fragments is android.app.Fragment. For special purposes you can
also use more special classes, like ListFragment or DialogFragment.
The onCreateView() method is called by Android once the Fragment should create its
user interface. Here you can inflate an layout. The onStart() method is called once the Fragment gets visible.
Fragments can be dynamically added and removed from
an Activity via Fragment transactions. This will add the action to the history stack of
the Activity, i.e. this will allow to revert the Fragment changes in theActivity via the
back button.
17.2. When to use Fragments
Fragments make it easy to re-use components in different layouts, e.g. you can build
single-pane layouts for handsets (phones) and multi-pane layouts for tablets.
This is not limited to tablets; for example you can use Fragments also to support
different layout for landscape and portrait orientation. But as tablets offer significantly
more space you typically include more views into the layout andFragments makes that
easier.
The typical example is a list of items in an activity. On a tablet you see the details
immediately on the same screen on the right hand side if you click on item. On a
handset you jump to a new detail screen. The following discussion will assume that you
have two Fragments (main and detail) but you can also have more. We will also have
one main activity and one detailed activity. On a tablet the main activity contains
both Fragments in its layout, on a handheld it only contains the main fragment.
To check for an fragment you can use the FragmentManager.
DetailFragment fragment = (DetailFragment) getFragmentManager().
findFragmentById(R.id.detail_frag);
if (fragment==null || ! fragment.isInLayout()) {
// start new Activity
}
else {
fragment.update(...);
}
To create different layouts with Fragments you can:
Use one activity, which displays two Fragments for tablets and only one on
handsets devices. In this case you would switch the Fragments in the activity
whenever necessary. This requires that the fragment is not declared in the layout
file as such Fragments cannot be removed during runtime. It also requires an
update of the action bar if the action bar status depends on the fragment.
Use separate activities to host each fragment on a handset. For example, when
the tablet UI uses twoFragments in an activity, use the same activity for handsets,
but supply an alternative layout that includes just one fragment. When you need
to switch Fragments, start another activity that hosts the other fragment.
The second approach is the most flexible and in general preferable way of
using Fragments. In this case the main activity checks if the detail fragment is available
in the layout. If the detailed fragment is there, the main activity tells the fragment that is
should update itself. If the detail fragment is not available the main activity starts the
detailed activity.
It is good practice that Fragments do not manipulate each other. For this purpose
a Fragment typically implements an interface to get new data from its host Activity.
18. Fragments Tutorial
18.1. Overview
The following tutorial demonstrates how to use Fragments. The
entry Activity (called MainActivity of our application ) will use different layouts for
portrait and for landscape mode.
In portrait mode MainActivity will show one Fragment with a list of names. If the user
touches an item in the list, a second Activity called DetailActivity will start and show
the selected text.
In landscape mode MainActivity will show two Fragments. The first is again
the Fragments which shows the list of names. The second Fragment shows the text of
the current selected item. This is similar to the portrait mode, but the whole information
will be shown on one screen.
18.2. Create project
Create a new project de.vogella.android.fragments with
an Activity called MainActivity.
18.3. Create layouts for landscape mode
Create or change the following layout files in the "res/layout/" folder.
First create the following file called "details.xml". This layout will be used by
the DetailFragment.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/detailsText"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="center_horizontal|center_vertical"
android:layout_marginTop="20dip"
android:text="Large Text"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textSize="30dip" />
</LinearLayout>
Change the existing "main.xml" file. This layout will be used by MainActivity in
landscape mode and shows twoFragments.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
<fragment
android:id="@+id/listFragment"
android:layout_width="150dip"
android:layout_height="match_parent"
android:layout_marginTop="?android:attr/actionBarSize"
class="de.vogella.android.fragments.ListFragment" ></fragment>
<fragment
android:id="@+id/detailFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
class="de.vogella.android.fragments.DetailFragment" >
<!-- Preview: layout=@layout/details -->
</fragment>
</LinearLayout>
18.4. Create Fragment classes
Create now the Fragment classes. Create the ListFragment class.
package de.vogella.android.fragments;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class ListFragment extends android.app.ListFragment {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
"Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
"Linux", "OS/2" };
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(),
android.R.layout.simple_list_item_1, values);
setListAdapter(adapter);
}
@Override
public void onListItemClick(ListView l, View v, int position, long id) {
String item = (String) getListAdapter().getItem(position);
DetailFragment fragment = (DetailFragment) getFragmentManager()
.findFragmentById(R.id.detailFragment);
if (fragment != null && fragment.isInLayout()) {
fragment.setText(item);
} else {
Intent intent = new Intent(getActivity().getApplicationContext(),
DetailActivity.class);
intent.putExtra("value", item);
startActivity(intent);
}
}
}
Create the DetailFragment class.
package de.vogella.android.fragments;
import android.app.Fragment;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class DetailFragment extends Fragment {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.e("Test", "hello");
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.details, container, false);
return view;
}
public void setText(String item) {
TextView view = (TextView) getView().findViewById(R.id.detailsText);
view.setText(item);
}
}
18.5. Create layouts for landscape mode
We want that Android uses a different main.xml file in portrait model then in landscape
mode.
For this reason create the "res/layout-port" folder.
In portrait mode Android will check the "layout-port" folder for fitting layout files. Only if
we would not have a "main.xml" file in "layout-port", Android would check the "layout"
folder.
Therefore create the following "main.mxl" layout file in "res/layout-port".
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
<fragment
android:id="@+id/listFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="?android:attr/actionBarSize"
class="de.vogella.android.fragments.ListFragment" />
</LinearLayout>
Also create the "details_activity_layout.xml" layout file. This layout will be used in
the DetailActivity which is only used in portrait mode. Please note that we could have
create this file also in the "layout" folder, but as it is only used in portrait mode it is best
practise to place it into this folder.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<fragment
android:id="@+id/detailFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
class="de.vogella.android.fragments.DetailFragment" />
</LinearLayout>
18.6. Activities
Create a new Activity called DetailActivity with the following class.
package de.vogella.android.fragments;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class DetailActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.details_activity_layout);
Bundle extras = getIntent().getExtras();
if (extras != null) {
String s = extras.getString("value");
TextView view = (TextView) findViewById(R.id.detailsText);
view.setText(s);
}
}
}
MainActivity will remain unmodified.
package de.vogella.android.fragments;
import android.app.Activity;
import android.os.Bundle;
public class MainActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
18.7. Run
Run your example. If you run the application in portrait mode you should see only
one Fragment. Use Ctrl+F11 to switch the orientation. In horizontal mode you should see
two Fragments. If you select an item in portrait mode a new Activity should get started
with the selected item. In horizontal mode your second Fragment should display the
select item.
19. DDMS perspective and important views
19.1. DDMS - Dalvik Debug Monitor Server
Eclipse provides a perspective for interacting with your Android (virtual) device and your
Android application program. Select Window → Open Perspective → Other → DDMS to
open this perspective. It includes severalViews which can also be used independently
and allows for example the application to place calls and send SMS to the device. It
also allows the application to set the current geo position and allows you to perform a
performance trace of your application.
19.2. LogCat View
You can see the log (including System.out.print() statements) via the LogCat view.
20. Shell
20.1. Android Debugging Bridge - Shell
You can access your Android emulator also via the console. Open a shell, switch to
your "android-sdk" installation directory into the folder "tools". Start the shell via the
following command "adb shell".
adb shell
You can also copy a file from and to your device via the following commands.
// Assume the gesture file exists on your Android device
adb pull /sdcard/gestures ~/test
// Now copy it back
adb push ~/test/gesture /sdcard/gestures2
This will connect you to your device and give you Linux command line access to the
underlying file system, e.g. ls, rm, mkdir, etc. The application data is stored in the
directory "/data/data/package_of_your_app".
If you have several devices running you can issue commands to one individual device.
# Lists all devices
adb devices
#Result
List of devices attached
emulator-5554 attached
emulator-5555 attached
# Issue a command to a specific device
adb -s emulator-5554 shell
20.2. Uninstall an application via adb
You can uninstall an android application via the shell. Switch the data/app directory
(cd /data/app) and simply delete your android application.
You can also uninstall an app via adb with the package name.
adb uninstall <packagename>
20.3. Emulator Console via telnet
Alternatively to adb you can also use telnet to connect to the device. This allows you to
simulate certain things, e.g. incoming call, change the network "stability", set your
current geocodes, etc. Use "telnet localhost 5554" to connect to your simulated device.
To exit the console session, use the command "quit" or "exit".
For example to change the power settings of your phone, to receive an sms and to get
an incoming call make the following.
# connects to device
telnet localhost 5554
# set the power level
power status full
power status charging
# make a call to the device
gsm call 012041293123
# send a sms to the device
sms send 12345 Will be home soon
# set the geo location
geo fix 48 51
For more information on the emulator console please see Emulator Console manual
21. Deploy your application on a real device
Turn on "USB Debugging" on your device in the settings. Select in the settings
Applications > Development, then enable USB debugging. You also need to install the
driver for your mobile phone. For details please see Developing on a Device . Please
note that the Android version you are developing for must be the installed version on
your phone.
To select your phone, select the "Run Configurations", select "Manual" selection and
select your device.
22. Thank you
Please help me to support this article:
23. Questions and Discussion
Before posting questions, please see the vogella FAQ. If you have questions or find an
error in this article please use the www.vogella.de Google Group. I have created a short
list how to create good questions which might also help you.
24. Links and Literature
24.1. Source Code
Source Code of Examples
24.2. Android Resources
Android 2 (German Book)
Android ListView and ListActivity
Android SQlite Database
Android Widgets
Android Live Wallpaper
Android Services
Android Location API and Google Maps
Android Intents
Android and Networking
Android Homepage
Android Developer Homepage
Android Issues / Bugs
Android Google Groups
Android Live Folder
24.3. vogella Resources
Eclipse RCP Training (German) Eclipse RCP Training with Lars Vogel
Android Tutorial Introduction to Android Programming
GWT Tutorial Program in Java and compile to JavaScript and HTML
Eclipse RCP Tutorial Create native applications in Java
JUnit Tutorial Test your application
Git Tutorial Put everything you have under distributed version control system