The activity class
0 likes88 views
This document summarizes key concepts about activities in Android, including: - Activities provide visual interfaces for user interaction and each typically supports a single focused task like viewing email or logging in. - Applications comprise multiple activities and Android supports navigation between them using tasks and a back stack. - Activities go through a lifecycle of creation, destruction, and state changes that Android manages through callback methods like onCreate(), onStart(), onResume(), etc. - Developers start new activities by creating intents and calling methods like startActivity(), and can get return values from started activities using startActivityForResult(). - Android may reconfigure or destroy activities in response to device configuration changes like orientation, so
The activity class
- 4. The activity class The task backstack The activity lifecycle Starting activities Handling configuration changes
- 5. Provides a visual interface for user interaction
- 6. Each activity typically supports one focused thing a user can do, such as Viewing an email message Showing a login screen
- 7. Applications often comprise several activities
- 8. Android supports navigation in several ways: Tasks The task backstack Suspending & resuming activities
- 9. A Task is a set of related Activities These related activities don’t have to be part of the same application Most tasks start at the home screen See: http://developer.android.com/guide/topics/ fundamentals/tasks-and-back-stack.html
- 10. When an Activity is launched, it goes on top of the backstack When the Activity is destroyed, it is popped off the backstack
- 11. Activity 3 Activity 2 Activity 1 Activity 1 Activity 2Activity 1
- 12. Activities are created, suspended, resumed & destroyed as necessary when an application executes
- 13. Some of these actions depend on user behavior Some depend on Android e.g., Android can kill activities when it needs their resources
- 14. Resumed/Running - visible, user interacting Paused - visible, user not interacting, can be terminated* Stopped - not visible, can be terminated
- 15. Android announces activity lifecycle state changes to activity by calling specific activity methods
- 16. protected void onCreate (Bundle savedInstanceState) protected void onStart() protected void onResume() protected void onPause() protected void onRestart() protected void onStop() protected void onDestroy()
- 19. Entire Lifetime
- 20. Visible
- 26. Called when Activity is created Sets up Initial state Call super.onCreate() Set the Activity’s content view Retain references to UI views as necessary Configure views as necessary
- 27. MapLocation
- 28. Called if the Activity has been stopped and is about to be started again Typical actions Special processing needed only after having been stopped
- 29. Activity is about to become visible Typical actions Start when visible-only behaviors Loading persistent application state
- 30. Activity is visible and about to start interacting with user Typical actions Start foreground-only behaviors
- 31. Focus about to switch to another Activity Typical actions Shutdown foreground-only behaviors Save persistent state
- 32. Activity is no longer visible to user may be restarted later Typical actions Cache state Note: may not be called if Android kills your application
- 33. Activity is about to be destroyed Typical actions Release Activity resources Note: may not be called if Android kills your application
- 34. MapLocation
- 35. MapLocation
- 36. Create an Intent object specifying the Activity to start
- 37. Pass newly created Intent to methods, such as: startActivity() startActivityForResult() Invokes a Callback method when the called Activity finishes to return a result
- 38. MapLocation
- 39. Similar to MapLocation, but gets address from contacts database
- 42. Started Activity can set its result by calling Activity.setResult() public final void setResult (int resultCode) public final void setResult (int resultCode, Intent data)
- 43. resultCode (an int) RESULT_CANCELED RESULT_OK RESULT_FIRST_USER Custom resultCodes can be added
- 46. Keyboard, orientation, locale, etc. Device configuration can change at runtime On configuration changes, Android usually kills the current Activity & then restarts it
- 47. Activity restarting should be fast If necessary you can: Retain an Object containing important state information during a configuration change Manually handle the configuration change
- 48. Hard to recompute data can be cached to speed up handling of configuration changes Override onRetainNonConfigurationInstance() to build & return configuration Object Will be called between onStop() and onDestroy()
- 49. Call getLastNonConfigurationInstance() during onCreate() to recover retained Object Note: These methods have been deprecated in favor of methods in the Fragment class (discussed in later classes)
- 50. Can prevent system from restarting Activity Declare the configuration changes your Activity handles in AndroidManifest.xml file, e.g., <activity android:name=".MyActivity“" android:configChanges=" "orientation|screensize|keyboardHidden”…>
- 51. When configuration changes, Activity’ s onConfigurationChanged() method is called Passed a Configuration object specifying the new device configuration
- 52. The Intent Class