life cycle method of activity

onRestart()

Called after onStop when the current activity is being re-displayed to the user (the user has navigated back to it). It will be followed by onStart and then onResume.

onStart()

Called after onCreate — or after onRestart when the activity had been stopped, but is now again being displayed to the user. It will be followed by onResume.

onResume()

Called after onRestoreInstanceState, onRestart, onStart, or onPause, for your activity to start interacting with the user. This is a good place to begin animations, open exclusive-access devices (such as the camera), etc.

onNetIntent(Intent intent)

This is called for activities that set launchMode to "singleTop" in their package, or if a client used the Intent.FLAG_ACTIVITY_SINGLE_TOP flag when calling startActivity. In either case, when the activity is re-launched while at the top of the activity stack instead of a new instance of the activity being started, onNewIntent() will be called on the existing instance with the Intent that was used to re-launch it.

An activity will always be paused before receiving a new intent, so you can count on onResume being called after this method.

Note that getIntent still returns the original Intent. You can use setIntent to update it to this new Intent.

onRestoreInstanceState(Bundle savedInstanceState)

This method is called after onStart when the activity is being re-initialized from a previously saved state, given here in savedInstanceState. Most implementations will simply use onCreate to restore their state, but it is sometimes convenient to do it here after all of the initialization has been done or to allow subclasses to decide whether to use your default implementation. The default implementation of this method performs a restore of any view state that had previously been frozen by onSaveInstanceState.

This method is called between onStart and onPostCreate.

onSaveInstanceState(Bundle savedInstanceState)

Called to retrieve per-instance state from an activity before being killed so that the state can be restored in onCreate or onRestoreInstanceState (the Bundle populated by this method will be passed to both).

This method is called before an activity may be killed so that when it comes back some time in the future it can restore its state. For example, if activity B is launched in front of activity A, and at some point activity A is killed to reclaim resources, activity A will have a chance to save the current state of its user interface via this method so that when the user returns to activity A, the state of the user interface can be restored via onCreate or onRestoreInstanceState.

Do not confuse this method with activity lifecycle callbacks such as onPause, which is always called when an activity is being placed in the background or on its way to destruction, or onStop which is called before destruction. One example of when onPause and onStop is called and not this method is when a user navigates back from activity B to activity A: there is no need to call onSaveInstanceState on B because that particular instance will never be restored, so the system avoids calling it. An example when onPause is called and not onSaveInstanceState is when activity B is launched in front of activity A: the system may avoid calling onSaveInstanceState on activity A if it isn't killed during the lifetime of B since the state of the user interface of A will stay intact.

The default implementation takes care of most of the UI per-instance state for you by calling android.view.View.onSaveInstanceState() on each view in the hierarchy that has an id, and by saving the id of the currently focused view (all of which is restored by the default implementation of onRestoreInstanceState). If you override this method to save additional information not captured by each individual view, you will likely want to call through to the default implementation, otherwise be prepared to save all of the state of each view yourself.

If called, this method will occur before onStop. There are no guarantees about whether it will occur before or after onPause.

onPause()

Called as part of the activity lifecycle when an activity is going into the background, but has not (yet) been killed. The counterpart to onResume.

When activity B is launched in front of activity A, this callback will be invoked on A. B will not be created until A's onPause returns, so be sure to not do anything lengthy here.

This callback is mostly used for saving any persistent state the activity is editing, to present a "edit in place" model to the user and making sure nothing is lost if there are not enough resources to start the new activity without first killing this one. This is also a good place to do things like stop animations and other things that consume a noticeable amount of CPU in order to make the switch to the next activity as fast as possible, or to close resources that are exclusive access such as the camera.

In situations where the system needs more memory it may kill paused processes to reclaim resources. Because of this, you should be sure that all of your state is saved by the time you return from this function. In general onSaveInstanceState is used to save per-instance state in the activity and this method is used to store global persistent data (in content providers, files, etc.)

After receiving this call you will usually receive a following call to onStop (after the next activity has been resumed and displayed), however in some cases there will be a direct call back to onResume without going through the stopped state.

onStop()

Called when you are no longer visible to the user. You will next receive either onRestart, onDestroy, or nothing, depending on later user activity.

Note that this method may never be called, in low memory situations where the system does not have enough memory to keep your activity's process running after its onPause method is called.

onDestroy()

Perform any final cleanup before an activity is destroyed. This can happen either because the activity is finishing (someone called finish on it), or because the system is temporarily destroying this instance of the activity to save space. You can distinguish between these two scenarios with the isFinishing method.

Note: do not count on this method being called as a place for saving data! For example, if an activity is editing data in a content provider, those edits should be committed in either onPause or onSaveInstanceState, not here. This method is usually implemented to free resources like threads that are associated with an activity, so that a destroyed activity does not leave such things around while the rest of its application is still running. There are situations where the system will simply kill the activity's hosting process without calling this method (or any others) in it, so it should not be used to do things that are intended to remain around after the process goes away.