INTRODUCTION TO ANDROID DEVELOPMENT

Jim McKeeth@JimMcKeeth

jim@mckeeth.org

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Tuesday, August 20, 13

AGENDA

• Hello Android

• Overview of Platform

• Platform Tools

• UI - XML

• Views & Widgets

• Architecture

• Manifest & Permission

• Activities & Intents

• Debugging

• Resources

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Tuesday, August 20, 13

ABOUT ME• Live here in Boise - jim@mckeeth.org

• Lead Developer Evangelist for Embarcadero Technologies

• www.embarcadero.com - Delphi for Android coming soon

• Google Developer Group - www.gdgb.org

• Boise Software Developers Group - www.bsdg.org

• Boise Code Camp - www.BoiseCodeCamp.com

Tuesday, August 20, 13

DEMO: HELLO ANDROID

Tuesday, August 20, 13

GOOD PLACES TO KNOW

• developer.android.com - Official developer site

• developers.google.com/android/ - Google on Android

• developers.google.com/events/io/ - Google I/O Replays

• stackoverflow.com - Great Q&A community

• android.stackexchange.com - End user Q&A

• vogella.com/android.html - Detailed tutorials5

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ANDROID

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ANDROID STACK

• Tweaked Linux 2.6

• Tweaked Java (Dalvik)

• Android OS

• Android Apps

• (Mostly open source)

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VERSION HISTORY

• November 5th, 2007 is Android’s Birthday

• Each version has a version number, name and API level

• Version number is most specific

• Name is group of versions and API levels

• Latest: Android 4.3 Jelly Bean (API 18)

http://en.wikipedia.org/wiki/Android_version_history#Version_history_by_API_levelTuesday, August 20, 13

VERSION POPULARITY

As of August 2013http://sn.im/platform-versions9

40% = Jelly Bean63% >= ICS96% >= Gingerbread

40%

23%

33%

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ARCHITECTUREhttp://sn.im/what-is-android

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FRAMEWORK• Dalvik VM

• WebKit Browser

• 2d Graphics Library, 3D w/OpenGL

• SQLite

• MPEG4, MP3, PNG, JPEG, etc

• GSM Telephony, Bluetooth, WiFi

• Camera, GPS, Compass, Accelerometer12

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CORE APPLICATIONS

• Phone

• eMail and SMS clients

• Calendar

• Contacts

• Web Browser

• Geographic Support via Google Maps13

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ANDROID DEVELOPMENT

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ANDROID SDK

• http://developer.android.com/sdk

• 3 Options

• ADT Bundle (in Eclipse)

• “Existing IDE” download

• Android Studio preview (in IntelliJ)

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RELATED TOOLS

• Managers

• Android SDK Manager

• AVD Manager (Android Virtual Device)

• Command-Line Tools

• adb (Android Debug Bridge - Your best friend!)

• Others

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ANDROID DEVELOPMENT

JDK$ Android'SDK'

Dalvik'Virtual'Machine'

Linux&kernel&

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BUILD PROCESS

Android'App'Package'

APK'

DEX'Compiler'

Dalvik'byte'code'

Java'Compiler'

Java'JAR'

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THE APK FILE

• Zip file containing

• Manifest, etc.

• Compiled code

• Resources & Assets

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ACTIVITY ARCHITECTURE

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Applica'on*Context*

PARTS OF AN ANDROID APP

Intent%

Ac#vity(

Class% Layout' String'Resources'

Android'Manifest'

Other&Classes&

Drawables)

Services(

Broadcast)Receiver)

Content&Providers&

Ac#vity( Intent%

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PROJECT LAYOUT

• AndroidManifest.xml

• bin (APK file, compiled DEX files)

• gen (generated resources)

• res (resources you create)

• src (Java source files)

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MANIFEST

• Mandatory XML file “AndroidManifest.xml”

• Describe application components

• Default Activity

• Permissions, Attributes

• Non-SDK libraries

http://sn.im/android-manifestTuesday, August 20, 13

MULTIPLE ACTIVITIES

• Each Activity must be defined in manifest by class name and “action”

• Activities reside on a “task stack” - visible activity is “top of stack”

• Transition to an Activity using Intent

• Return from Activity using Activity.finish() which pops off task stack

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“RES” - RESOURCES

• XML Files

• drawable

• layout

• values

• etc.

• Graphics

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RES/LAYOUT

• Each Activity should have dedicated layout XML file

• Layout file specifies Activity appearance

• Several layout types

• Default LinearLayout provides sequential placement of widgets

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RES/VALUES

• strings.xml contains String constants

• Prefer strings.xml to hardcoded values (warnings)

• L10N/I18N (Localization/Internationalization)

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• Application/Task is a stack of Activities

• Visible activity = top of stack

• Activities maintain state, even when not TOS

• “Back” button pops stack.

• “Home” key would move stack to background

• Selecting application brings to foreground or launches new instance

APPLICATION AKA TASK

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ANDROID.APP.ACTIVITY

• Activity extends Context

• Context contains application environment

• “a single focused thing a user can do”

• An application consists of 1 or more Activities

• Provides a default window to draw in, might be smaller than screen or float on top of others

• UI elements are “View(s)” or widgets

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ANDROID.VIEW.VIEW

• Extends java.lang.Object

• Basic building block for UI components

• Rectangular area on display

• Responsible for drawing and event handling

• View is the base class for widgets

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Callback Methods(delegates)

Major States

Activity Lifecycle

http://sn.im/android-activityTuesday, August 20, 13

SAVING STATE

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FRAGMENTS

http://sn.im/android-fragmentsTuesday, August 20, 13

ANDROID.CONTENT.INTENT

• Interprocess Communication messaging

• Can launch an Activity or start a Service

• new Intent(String action, Uri uri);

• new Intent(Context packageCtx, Class class);

• Intent.putExtra()

• Intent.setAction()http://sn.im/android-intent

Tuesday, August 20, 13

INTENT (CONTINUED)

• android.intent.action.MAIN (receiver on main activity)

• many options: ACTION_VIEW, etc

• category = extra information

• MIME type

• extras (i.e. getAction(), getExtra(), etc)

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INTENT USAGE• Activity Switch:• new Intent(this, NextActivity.class);• Web Browser:

• Uri uri = Uri.parse(“http://foobar.com”);• new Intent(Intent.ACTION_VIEW, uri);

• Phone Dialer :• Uri uri = Uri.parse(“tel:4085551212”); • new Intent(Intent.ACTION_VIEW, uri);

http://sn.im/android-intentTuesday, August 20, 13

VIEWS

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VIEW LISTENERS

• GUI is event driven

• Event source: button press, mouse click, etc.

• Listener catches event and performs action

• Events are delivered to view w/current focus

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EVENT LISTENER• onClick()/View.OnClickListener()

• (boolean) onLongClick()/View.OnLongClickListener()

• onFocusChange()/View.OnFocusChangeListener()

• (boolean) onKey()/View.OnKeyListener()

• (boolean) onTouch()/View.OnTouchListener()

• onCreateContextMenu()/View.OnCreateContextMenuListener()

• return true to stop event propagation

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VIEW SIZE

• FILL_PARENT = parent sized (minus pad)

• Now “MATCH_PARENT” w/API Level 8

• WRAP_CONTENT = just big enough (plus pad)

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LAYING OUT VIEWS

• Gravity = position (i.e. left, right, center)

• Weight = extra/empty space allocation

• priority for expansion

• default weight is zero

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DIMENSION VALUES

• Dimension values:

• dp/dip = density independent pixels

• sp = Scale independent pixels

• px = pixels

• in/mm = inches/millimeters

• pt = point (1/72 inch)

Reco

mmen

ded

Not

Reco

mmen

ded

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DENSITY INDEPENDENT PIXELS

• An abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi (dots per inch) screen, so 160dp is always one inch regardless of the screen density.

• The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct proportion.

• You should use these units when specifying view dimensions in your layout, so the UI properly scales to render at the same actual size on different screens.

• The compiler accepts both "dip" and "dp", though "dp" is more consistent with "sp".

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SCALE-INDEPENDENT PIXELS

• This is like the dp unit, but it is also scaled by the user's font size preference.

• Recommend you use this unit when specifying font sizes, so they will be adjusted for both the screen density and the user's preference.

Recom

mend

ed

for Fo

nts

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COLORS

• #RGB

• #ARGB ( Alpha / Red / Green / Blue )

• #RRGGBB (i.e. #3d1ec4)

• #AARRGGBB

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VIEW / VIEWGROUP

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LAYOUTS (VIEWGROUPS)• AbsoluteLayout -Absolute X, Y (depreciated)• FrameLayout - Pinned to top left (simplest)• LinearLayout - Horizontal or Vertical - one per row• RelativeLayout - Child specify relative widgets• SlidingDrawer - Hides until dragged out by handle• TableLayout - Rows & Columns• ScrollView - Child can be larger than window• TabWidget - Manages collection of “Tab Hosts”

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ORIENTATION

• landscape or portrait

• dedicated layout file

• /res/layout = default layout directory

• /res/layout-land = landscape layout directory

• /res/layout-port = portrait layout directory

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DEMO - LAYOUTS & VIEWS

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TRACE LOGGING• android.util.Log

• Log.d(“tag”, “debug”);

• Log.e(“tag”, “error”);

• Log.i(“tag”, “informational”);

• Log.v(“tag”, “verbose”);

• Log.w(“tag”, “warning”);

• View output using “adb logcat”http://sn.im/android-log

Tuesday, August 20, 13

ADB - ANDROID DEBUG BRIDGE

• Manages devices & emulators

• Issue debug commands

• Log output (adb logcat)

• Shell (adb shell)

• Copy files to/from emulator (adb push/pull)

http://sn.im/android_debug_bridgeTuesday, August 20, 13

DEMO - ADB & LOGCAT

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BEST PRACTICES

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BEST PRACTICES

• Support multiple screen sizes and densities

• Use the Action Bar pattern - Good-bye menu button

• Build Dynamic UI with Fragments

• Know when to persist and restore state

• Don’t block main thread - use AsyncTask - Test with StrictMode

http://sn.im/android-practiceshttp://sn.im/android-performance

Tuesday, August 20, 13

SUPPORT MULTIPLE SCREENSSIZES & DENSITIES

• Use wrap_content, fill_parent, or dp units when specifying dimensions in an XML layout file

• Do not use hard coded pixel values in your application code

• Do not use AbsoluteLayout (it's deprecated)

• Supply alternative bitmap drawables for different screen densities

• ldpi, mdpi, hdpi, xhdpihttp://sn.im/android-screens

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SCREEN SIZES & DENSITIES

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ACTION BAR

1. App Icon - optional “up” affordance

2. View control - Navigation

3. Dynamic number of “important” action buttons

4. Action overflowhttp://sn.im/android-actionbar

http://actionbarsherlock.com/

Tuesday, August 20, 13

ASYNC TASKprivate class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {

     protected Long doInBackground(URL... urls) {         int count = urls.length;         long totalSize = 0;         for (int i = 0; i < count; i++) {             totalSize += Downloader.downloadFile(urls[i]);             publishProgress((int) ((i / (float) count) * 100));             // Escape early if cancel() is called             if (isCancelled()) break;         }         return totalSize;     }

     protected void onProgressUpdate(Integer... progress) {         setProgressPercent(progress[0]);     }

     protected void onPostExecute(Long result) {         showDialog("Downloaded " + result + " bytes");     } } http://sn.im/android-asynctask

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STRICT MODE

• Place a policy on a thread - provides feedback when blocked

 public void onCreate() {

     if (DEVELOPER_MODE) {         StrictMode.enableDefaults(); // Or configure     }     super.onCreate(); }

• http://sn.im/android-strictmode

• http://sn.im/android-strictmode-blog

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FIN.

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GOOD PLACES TO KNOW

• developer.android.com - Official developer site

• developers.google.com/android/ - Google on Android

• developers.google.com/events/io/ - Google I/O Replays

• stackoverflow.com - Great Q&A community

• android.stackexchange.com - End user Q&A

• vogella.com/android.html - Detailed tutorials61

Tuesday, August 20, 13

ABOUT ME• Live here in Boise - jim@mckeeth.org

• Lead Developer Evangelist for Embarcadero Technologies

• www.embarcadero.com - Delphi for Android coming soon

• Google Developer Group - www.gdgb.org

• Boise Software Developers Group - www.bsdg.org

• Boise Code Camp - www.BoiseCodeCamp.com

Tuesday, August 20, 13