The document provides an overview of Android Activities, covering their definition, lifecycle, and management including starting, shutting down, and state saving. It outlines methods for creating activities and handling results, as well as tips for configuration changes and back stack management. Additionally, it includes homework assignments to illustrate back stack scenarios with various activity launch modes.

1. Android platform
Activity
Cao Minh Vu
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cmv.ict@gmail.com

2. Outline
 What is activity
 Starting activity
 Shutting down activity
 Activity lifecycle
 Save state
 Back stack
 Tips
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3. What is activity
 An application component
 A screen with which user can interact
 A window to draw its UI
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4. Creating an activity
 Declare in manifest.xml
 Implement xml layout (optional)
 Extends from Activity
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5. Starting an activity
 By name
Intent intent = new Intent(this, SignInActivity.class);
startActivity(intent);
 By action
Intent intent = new Intent(“com.multi.action_show”);
startActivity(intent);
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6. Starting an activity (cont)
 Start for result
Intent intent = new Intent((Intent.ACTION_PICK);
intent.setType(“video/*”);
startActivityForResult(intent, requestCode);
protected void onActivityResult(int requestCode, int
resultCode, Intent data) {
}
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7. Shutting down an activity
 Explicitly
 Finish();
 Implicitly
 Let the system do it (when user press BACK HW)
 Force Close
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8. Activity lifecycle
 onCreate(Bundle savedInstanceState)
 initialize the essential components
 setContentView();
 onResume()
 just before the activity starts interacting with the
user (foreground)
 OnPause()
 Another activity is in the foreground + focus, but this
one is still visible => completely alive
 partially transparent or doesn't cover the entire 8
screen

9. Activity lifecycle (cont)
 OnStop()
 completely obscured by another activity
(=>background)
 is not attached to the window manager
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10. Activity lifecycle (cont)
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11. Save state
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12. Back stack
 Android Manifest
 "standard" (the default mode)
 "singleTop"
 "singleTask"
 "singleInstance"
 Flag
 FLAG_ACTIVITY_NEW_TASK (single task)
 FLAG_ACTIVITY_SINGLE_TOP (single top)
 FLAG_ACTIVITY_CLEAR_TOP
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13. Configuration change
 Screen orientation, change language...
 Call onDestroy and onCreate()
 Avoid ?
<activity android:name=".CustomGalleryActivity"
android:configChanges="keyboardHidden|
orientation"/>
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14. Homework
 Given activities started in order: A->B-C->D
Draw the back stack to illustrate 2 cases:
 1. Start new activity D
 2. Start new activity B
with modes: standard, singleTop, singleTask,
singleInstance and Flag:
FLAG_ACTIVITY_NEW_TASK,
FLAG_ACTIVITY_SINGLE_TOP,
FLAG_ACTIVITY_CLEAR_TOP
Requirement:
 Draw back stack state when start new activity and
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then press back HW until the program is closed

15. Tips
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16. Reference
 http://developer.android.com/guide/topics/funda
mentals/activities.html
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