Android intents

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Android intents

  1. 1. Android Intents
  2. 2. Agenda What is Intent? Why Intent? Types of Intents? How Intents are received? How Intents are resolved?
  3. 3. What is an Intent? ➢ Intent is an intention to do something. ➢ Intent contains an action carrying some information. ➢ Intent is used to communicate between android components. ○ To start an activity ○ To start a service ○ To deliver a broadcast.
  4. 4. Why Intent? ➢ Intent is used to communicate, share data between components. ➢ Intent contains the following things. ○ Component Name ○ Action ○ Data ○ Extras ○ Category ○ Flags
  5. 5. Types of Intents? ➢ Explicit Intents ➢ Implicit Intents
  6. 6. Explicit Intents ➢ Used to launch a specific component like activity or a service. ➢ In this case, android system directly forwards this intent to that specific component. ➢ It is faster. ➢ Always use explicit intents if you know the specific activity or service that performs
  7. 7. Explicit Intents ➢ To Create Explicit intents // Executed in an Activity, so 'this' is the Context // The fileUrl is a string URL, such as "http://www.example.com/image.png" Intent downloadIntent = new Intent(this, DownloadService.class); downloadIntent.setData(Uri.parse(fileUrl)); startService(downloadIntent);
  8. 8. Implicit Intent ➢ Specifies an action that can invoke an app on the device that can perform the action. ➢ Useful when your app can not perform the action but other apps do and you let user to pick up the app. ➢ Its possible that there may not be any app that handles the implicit intent.
  9. 9. Implicit Intent Ex: // Create the text message with a string Intent sendIntent = new Intent(); sendIntent.setAction(Intent.ACTION_SEND); sendIntent.putExtra(Intent.EXTRA_TEXT, textMessage); sendIntent.setType(HTTP.PLAIN_TEXT_TYPE); // "text/plain" MIME type // Verify that the intent will resolve to an activity if (sendIntent.resolveActivity(getPackageManager()) != null) { startActivity(sendIntent); }
  10. 10. How Intents are received? ➢ Till now we have seen how intents are used to invoke some other components. Now lets explore how these components receive these intents. ➢ Receiving Implicit Intents ➢ Receiving Explicit Intents ○ Explicit Intents are directly delivered to target as intent has the target component class specified in it.
  11. 11. Receiving Implicit Intents ➢ Your app should advertise what intents it can handle using <intent-filter> tag in the manifest file under <activity> or <service> or <receiver> tags. ➢ You can mention one or more of these three elements under <intent-filter> ○ action ○ data ○ category
  12. 12. Receiving Implicit Intents Ex: <activity android:name="ShareActivity"> <intent-filter> <action android:name="android.intent.action.SEND"/> <category android:name="android.intent.category.DEFAULT"/> <data android:mimeType="text/plain"/> </intent-filter> </activity>
  13. 13. How Intents are resolved? ➢ When the system receives an implicit intent, it searches the component by comparing the intent to intent filter based on these aspects. ○ The Intent action(Action Test) ■ Ex: ACTION_SEND ○ The Intent Category(Category Test) ■ Ex: CATEGORY_HOME ○ The Data(Data Test) ■ Ex: android:mimetype=”video/mpeg”
  14. 14. Further Study ➢ Explore on Pending Intents. ➢ Writing your own intent chooser.

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