Android Activity and its lifecycle. understand various stages in lifecycle.

1. Activity
1
Sourabh Sahu

2. ?

What is started by the device

It contains the application's
information

Has method a to answer certain
events

An application could be composed
of multiple activities

3. Activity Life
Cycle

5. 
Resumed

The activity is in the foreground, and the user
can interact.

Paused

The activity is partially overlayed by another
activity. Cannot execute any code nor receive
inputs.

Stopped

Activity is hidden, in the background. It cannot
execute any code.

6. OnCreate()
 Called when the activity is
created
 Should contain the initialization
operations
 Has a Bundle parameter
 If onCreate() succesfull
terminates, it calls onStart()

7. 
OnStart()

Called when onCreate() terminates

Called right before it is visible to
user

If it has the focus, then onResume()
is called

If not, onStop() is called

8. OnResume()
 Called when the activity is
ready to get input from users
 Called when the activity is
resumed too
 If it succesfully terminates,
then the Activity is RUNNING

9. 
OnPause()

Called when another activity comes
to the foreground, or when
someone presses back

Commit unsaved changes to
persistent data

Stop cpu-consuming processes

Make it fast

10. 
OnRestart()

Similar to onCreate()

We have an activity that was
previously stopped

11. OnStop()
 Activity is no longer visible to the
user
 Could be called because:
 the activity is about to be
destroyed
 another activity comes to the
foreground

12. OnDestroy()
 The activity is about to be destroyed
 Could happen because:
 The systems need some stack space
 Someone called finish() method
on this activity
 Could check with isFinishing()

13. Mainly 3 different loops
Entire lifetime
 Between onCreate() and onDestroy().
 Setup of global state in onCreate()
 Release remaining resources in
onDestroy()
Visible lifetime
 Between onStart() and onStop().
 Maintain resources that has to be shown to
the user.
Foreground lifetime
 Between onResume() and onPause().
 Code should be light.

14. • Declare them before running them
• <activity android:name=".MainActivity"
android:label="@string/app_name">
• <intent-filter>
• <action
android:name="android.intent.action.MAIN"
/>
• <category
android:name="android.intent.category.LAUN
CHER" />
• </intent-filter>
• </activity>
In manifest file

15. • Open the MainActivity.java file in the
project, and override the
existing onStart method, which is called
when the activity is first viewed.
• Call the onStart method of the parent
class, and log a debug message:
• @Override
• public void onStart(){
super.onStart();
Log.d(CLASS_NAME, "onStart");
• }

16. • Override the existing onPause method,
which is called when another activity is
called to the foreground. Call
the onPause method of the parent and log
a debug message:
@Override
public void onPause(){
super.onPause();
Log.d(CLASS_NAME, "onPause");
}
• Override the existing onResume method, which is called
when the activity is running in the foreground and the user
can interact with it. Call the onResume method of the
parent class, and log a debug message:
• @Override public void onResume()
{ super.onResume();
• Log.d(CLASS_NAME, "onResume");
• }

17. Override the existing onStop method, which is called when the
activity is invisible to the end user. Call the onStop method of the
parent class, and log a debug message:
@Override public void onStop(){
super.onStop();
Log.d(CLASS_NAME, "onStop");
}
Override the existing onDestroy method, which is called when the
activity is removed from the system and can no longer be
interacted with. Call the onDestroy method of the parent class, and
log a debug message:
@Override public void onDestroy(){
super.onDestroy();
Log.d(CLASS_NAME, "onDestroy");
}
Override the existing onRestart method, which is called when the
activity is started again and returns to the foreground. Call
the onRestart method of the parent class and log a debug
message:
@Override public void onRestart(){
super.onRestart();
Log.d(CLASS_NAME, "onRestart"); }

18. Now Test & debug in Logcat

19. Thank You
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