Activity and its Lifecycle

                                              Activity and its Lifecycle

What is an Activity?

Which present something to you with which you can interact there call Activity.An application component that provides a screen

What they do.

You can draw different type of UI on its windows.Every app has 1 main activity and other activities.An ap can start any Activity belonging to certain conditions.When a new Activity starts,the previous Activity is stopped and added to stack knows as BackStack.

What is a callback method?

Android OS calls certain method on your Activity class to notify whether your app is running currently or not.

Just like JVM calling public static void main

General guidelines

1.       Don’t do heavy processing or network consuming operations when user is currently away from your app.

2.       App should not crash when another app is started.

3.       Don’t lose the user’s progress or session data.

Activity Lifecycle Methods

When user launch your apps for the first time now the user can launch your app from the app section or he can launch through widget or whatever so what happen when the user click your app icon. These three methods are called onCreate (), onStart (), onResume ().What happens when the user actually try to pause your app. So in this case onPause (), onStop () method are called. What happens when the user click the back button. So in this case these methods are called onRestart (), onStart (), onResume () in a quick.

What is Logcat?

Logcat is used for debugging purposes. We will use the logcat in activity to check the Activity Lifecycle Method. Logcat Print different messages using android.util.Log class.

Log.d (String tag, String message)

Log.d (“LIFECYCLE”, ”onCreate was called”);

There are other method in Logcat

1.     For information we can use Log.i(String tag, String message)

2.     For Error we can use Log.e(String tag, String message)

3.     For warning we can use Log.w(String tag, String message)

4.     For Verbose we can use Log.v(String tag, String message)

Activity Lifecycle Diagram

Example:

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.util.Log;

public class MainActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        Log.d("Android is simples","onCreate was called");

    }

    @Override

    protected void onResume() {

        super.onResume();

        Log.d("Android is simples","onResume was called");

    }

    @Override

    protected void onStart() {

        super.onStart();

        Log.d("Android is simples","onStart was called");

    }

    @Override

    protected void onPause() {

        super.onPause();

        Log.d("Android is simples","onPause was called");

    }

    @Override

    protected void onStop() {

        super.onStop();

        Log.d("Android is simples","onStop was called");

    }

    @Override

    protected void onRestart() {

        super.onRestart();

        Log.d("Android is simples","onRestart was called");

    }

    @Override

    protected void onDestroy() {

        super.onDestroy();

        Log.d("Android is simples","onDestroy was called");

    }

}