[Android] Intent and Activity

Android Programming

Lesson 6
Intent and Activity

NGUYEN The Linh

Android Programming

Contents

1 Understanding Intents

2 Activity

3 Exercise 6

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Intent and Activity

Understanding Intents

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http://blog.nikmesoft.com

Verbs URL

HTTP

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 Just as a Web browser knows how to process a verb
+ URL pair, Android knows how to find activities or
other application logic that will handle a given intent.

 You can use intents to represent actions.

 At the simplest level, an intent is an action that you
can tell Android to invoke.

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 Notes:
 android:exported: Whether or not the activity can be launched
by components of other applications — "true" if it can be, and
"false" if not.

 The general convention for an action name is <your-package-
name>.intent.action.YOUR_ACTION_NAME.

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 Available Intents in Android
 http://developer.android.com/guide/appendix/g-app-intents.html
 A browser application to open a browser window
 An application to call a telephone number
 An application to present a phone dialer so the user can enter
the numbers and make the call through the UI
 A mapping application to show the map of the world at a given
latitude/longitude coordinate
 A detailed mapping application that can show Google stree
views

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Event Listeners and Callback Methods

 Example 6.1 6.2

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 Using Extra Information
 An extra can provide more information to the component that
receives the intent.

 This extra information is repre-sented by an Android class called
android.os.Bundle.

 The following two methods on an Intentclass provide access to
the extra Bundle:

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 Using Extra Information (cont.)

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 Using Extra Information (cont.)

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 Using Components to Directly Invoke an Activity
 Android also provides a more direct way to start an activity: you
can specify the activity’s ComponentName, which is an
abstraction around an object’s package name and class name.

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(cont.)
 ComponentName wraps a package name and a class name
together. For example, the follow-ing code invokes the
SubActivity:

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(cont.)
 You can also use the class name directly without constructing a
ComponentName.

 You should register the activity in the AndroidManifest.xml file
like this:
• <activity android:name=".SubActivity">

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(cont.)

 No intent-filters are necessary for invoking an activity directly
through its class name or component name.

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Intent and Activity

Activity

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Activity

 Activity Lifecycle
 Most management of the life cycle is done automatically by the
system via the activity stack.
 The activity class has the following method callbacks to help you
manage the app:
• onCreate()
• onStart()
• onResume()
• onPause()
• onStop()
• onRestart()
• onDestroy()
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Activity

Activity
Lifecycle

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Activity

Saving
activity
state

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Activity

 Launching Activities and Sub-Activities(cont.)

Activity A Activity B Activity C

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Activity


Activity A Activity B

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Activity


Activity A Activity B

finish();
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Activity


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Activity

 The Request Code: The request code that was used to launch
the returning sub-Activity

 A Result Code: The result code set by the sub-Activity to
indicate its result. It can be any inte-ger value, but typically will
be either Activity.RESULT_OK or
Activity.RESULT_CANCELLED.

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Activity

 If the sub-Activity closes abnormally or doesn’t specify a result
code before it closes, the result code is
Activity.RESULT_CANCELED.

 Data: An Intent used to bundle any returned data.

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Exercise 6

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[Android] Intent and Activity

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