Lesson 1

Basic Blocks

Android App Development for Beginners

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Activities

An activity is the entry point for interacting with the user.

Activities - Instagram example

List of new post Create new post Profile information

Activities - Steps

1. Register the activity in the app’s manifest.

2. Manage activity lifecycles appropriately

Activities - Register the activity in the manifestDeclare the activity in the application's

manifest file adding an <activity> element as a child of the <application> element.

<?xml version="1.0" encoding="utf-8"?>

<manifest … >

<application … >

<activity android:name=".MoviesActivity" />

…

</application>

...

</manifest>

Activities - Manage Lifecycle

To create an android activity we need implement it as a subclass of the Activity class. This Activity class is part of the Android API classes.

Activities - onCreate()

The onCreate() callback fires when the system creates your activity

Activities - onStart()

This callback contains the activity’s final preparations for coming to the foreground and becoming interactive.

Activities - onResume()

The state in which the app interacts with the user is onResume().

Activities - onPause()

When an interruptive event occurs the system invokes the onPause()callback.

Activities - onStop()

When your activity is no longer visible to the user, it has entered the Stopped state, and the system invokes the onStop() callback.

Activities - onRestart()

In the onRestart() callback, the app restores the state of the activity from the time that it was stopped.

Activities - onDestroy()

The system invokes the onDestroy()callback before an activity is destroyed

Intents

An Intent is a messaging object you can use to request an action from another app component:

● Start an activity● Start a service● Delivering a broadcast

Intents - Start an activity

Intent i = new Intent(PostListActivity.this,

PostDetailActivity.class);

startActivity(i);and

Use startActivityForResult() to receive a result

Intents - Start a service and Deliver a broadcastA service is a component that performs

operations in the background without a user interface.

startService()

A broadcast is a message that any app can receive.

sendBroadcast()

or

sendOrderedBroadcast()

Intents - Explicit intents

Used to launch a specific app component, such as a particular activity or service in your app.

Intent downloadIntent = new Intent(this, DownloadService.class);

downloadIntent.setData(Uri.parse(fileUrl));

startService(downloadIntent);

Intents - Implicit intents

Intent sendIntent = new Intent();

sendIntent.setAction(Intent.ACTION_SEND);

sendIntent.putExtra(Intent.EXTRA_TEXT, textMessage);

sendIntent.setType("text/plain");

if (sendIntent.resolveActivity(getPackageManager()) != null) {

startActivity(sendIntent);

}

An implicit intent specifies an action that can invoke any app on the device able to perform the action.

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