The Activity Lifecycle

As a user navigates through, out of, and back to your app, the Activity instances in your app transition through different states in their lifecycle. The Activity class provides a number of callbacks that allow the activity to know that a state has changed: that the system is creating, stopping, resuming, or destroying an activity.

To navigate transitions between stages of the activity lifecycle, the Activity class provides a core set of six callbacks:

Activity Lifecycle Diagram

1. onCreate : This method called when activity first created.

2. onStart : This method called when activity visible to user.

3. onResume :  This method called when activity interacting with user.

4. onPause : This method called when activity not visible to user.

5. onStop : This method called when activity not longer visible to user.

6. onDestroy : This method called before activity destroyed.

Activity Lifecycle Example:

public class MainActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toast.makeText(this, "onCreate()", Toast.LENGTH_SHORT).show();
    }

    @Override

    protected void onStart() {

        super.onStart();
        Toast.makeText(this, "onStart()", Toast.LENGTH_SHORT).show();
    }

    @Override

    protected void onResume() {

        super.onPostResume();
        Toast.makeText(this, "onResume()", Toast.LENGTH_SHORT).show();
    }

    @Override

    protected void onPause() {

        super.onPause();
        Toast.makeText(this, "onPause()", Toast.LENGTH_SHORT).show();
    }

    @Override

    protected void onStop() {

        super.onStop();
        Toast.makeText(this, "onStop()", Toast.LENGTH_SHORT).show();
    }

    @Override

    protected void onDestroy() {

        super.onDestroy();
        Toast.makeText(this, "onDestroy()", Toast.LENGTH_SHORT).show();
    }
}