Android Activity Lifecycle

An activity is a single, focused thing that the user can do. Almost all activities interact with the user, so the Activity class takes care of creating a window for you in which you can place your UI with setContentView(View).

Background

Activity is a window that contains the user interface of your application. As there are various states of activity like Running, Paused, Stopped and Killed.

Activity base class contains events that govern the life cycle of an activity.

• onCreate(): Called when the activity is first created
• onStart(): Called when the activity becomes visible to the user
• onResume(): Called when the activity starts interacting with the user
• onPause(): Called when the current activity is being paused and the previous activity is being resumed
• onStop(): Called when the activity is no longer visible to the user
• onDestroy(): Called before the activity is destroyed by the system
• onRestart(): Called when the activity has been stopped and is restarting again

Using the Code

To create an activity, your class need to extends Activity base class. An Application has more than one activity.

packagesat.example.lifecycle;

importandroid.app.Activity;

importandroid.os.Bundle;

importandroid.util.Log;

importandroid.widget.Toast;

public class LifeCycleActivity extends Activity {

/** Called when the activity is first created. */

    @Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

Toast.makeText(LifeCycleActivity.this,"ON CREATE", Toast.LENGTH_SHORT).show();

    }

    @Override

protected void onStart() {

// TODO Auto-generated method stub

super.onStart();

Toast.makeText(LifeCycleActivity.this,"ON START", Toast.LENGTH_SHORT).show();

    }

    @Override

protected void onResume() {

// TODO Auto-generated method stub

super.onResume();

Toast.makeText(LifeCycleActivity.this,"ON RESUME", Toast.LENGTH_SHORT).show();

    }

    @Override

protected void onPause() {

// TODO Auto-generated method stub

super.onPause();

Toast.makeText(LifeCycleActivity.this,"ON PAUSE", Toast.LENGTH_SHORT).show();

    }

    @Override

protected void onRestart() {

// TODO Auto-generated method stub

super.onRestart();

Toast.makeText(LifeCycleActivity.this,"ON RESTART", Toast.LENGTH_SHORT).show();

    }

    @Override

protected void onStop() {

// TODO Auto-generated method stub

super.onStop();

Toast.makeText(LifeCycleActivity.this,"ON STOP", Toast.LENGTH_SHORT).show();

    }

    @Override

protected void onDestroy() {

// TODO Auto-generated method stub

super.onDestroy();

Toast.makeText(LifeCycleActivity.this,"ON DESTROY", Toast.LENGTH_SHORT).show();

    }

} 

1. When you run the following code, you see when the application starts there are three toast messages that come after one another. First is ON CREATE , second is ON START and third is ON RESUME.
2. When you press the home button from the emulator, ON PAUSE and ON STOP methods call.
3. And when you open the application again ON RESTART, ON START and ON RESUME methods call.
4. And at last, when you press the back button from emulator, ON PAUSE , ON STOP and ON DESTROY method calls.

 

It provides the details about the invocation of life cycle methods of activity. In this example, we are displaying the content on the logcat.

File: MainActivity.java

package com.example.activitylifecycle;   

  

import android.os.Bundle;   

import android.app.Activity;   

import android.util.Log;   

import android.view.Menu;   

  

public class MainActivity extends Activity {   

  

    @Override  

    protected void onCreate(Bundle savedInstanceState) {   

        super.onCreate(savedInstanceState);   

        setContentView(R.layout.activity_main);   

        Log.d("lifecycle","onCreate invoked");   

    }   

    @Override  

    protected void onStart() {   

        super.onStart();   

         Log.d("lifecycle","onStart invoked");   

    }   

    @Override  

    protected void onResume() {   

           

        super.onResume();   

         Log.d("lifecycle","onResume invoked");   

    }   

       

  

    @Override  

    protected void onPause() {   

           

        super.onPause();   

         Log.d("lifecycle","onPause invoked");   

    }   

    @Override  

    protected void onStop() {   

           

        super.onStop();   

         Log.d("lifecycle","onStop invoked");   

    }   

       

       @Override  

    protected void onRestart() {   

           

        super.onRestart();   

         Log.d("lifecycle","onRestart invoked");   

    }      

    @Override  

    protected void onDestroy() {   

           

        super.onDestroy();   

         Log.d("lifecycle","onDestroy invoked");   

    }   

}