Activity Behavior When Screen Orientation Changes In Android Application

Overview

Here, some useful links are given to start programming in Android Applications-.

Introduction

In this article, you will learn about an activity behavior of the views, when screen orientation changes to either portrait or a landscape. In the article Orientation, Anchoring, Resizing And Repositioning Of Views In Android Application, I talked about the different type of screen orientation. The activity life cycle, I have covered in this article, Android Programming - Day Two . Now, it’s very important to know about the activity’s state, when the device changes an orientation.

Implementation

Create a new project by selecting the File->New->New Project.

Add 2 EditText element in the activity_main.xml file. Change the layout as LinearLayout.

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/txt1"
/>
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/txt2"
/>
</LinearLayout>

Add the code, given below, in the MainActivity.java file,

package com.example.administrator.orientationapp;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.d("ChangeStateInfo","onCreate");
}
@Override
public void onStart(){
Log.d("ChangeStateInfo", "onStart");
super.onStart();
}
@Override
public void onResume(){
Log.d("ChangeStateInfo","onResume");
super.onResume();
}
@Override
public void onPause(){
Log.d("ChangeStateInfo","onResume");
super.onPause();
}
@Override
public void onStop(){
Log.d("ChangeStateInfo","onStop");
super.onStop();
}
@Override
public void onDestroy(){
Log.d("ChangeStateInfo","onDestroy");
super.onDestroy();
}
@Override
public void onRestart(){
Log.d("ChangeStateInfo","onRestart");
super.onRestart();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}

Explanation

Run the Application by clicking F11 on either Android Emulator or device. When the views are in portrait mode, it looks like the image, given below,

The state sequence is in the following order when the views are in the portrait state initially,

As soon as the state is changed from portrait to landscape, it looks like the image, given below,

The state sequence is in the following order,

From the above output, we see that the activity is destroyed or resumed when the device changes the orientation from landscape to portrait or vice versa.

Afterward, it again recreates.

Thus, it is very important to understand the behavior because you need to ensure that you take the necessary steps to preserve the state of your activity before it changes orientation. Suppose, your activity may have the variables that contain the values, required for some calculations in the activity. For any activity, you will have to save whatever state you need to save in the onResume() method, which is fired every time the activity changes an orientation.

There is another important behavior to understand. Is it only View which has some Id defined in an activity? They will have their state persisted when the activity they are contained in is destroyed or resumed. Suppose, the user may change an orientation while entering some text into an EditText View. When this happens, any text inside the EditText View will persist; and restored automatically when the activity is recreated.

Conclusion

In the article, you learned the activity behavior when the screen orientation changes. In the next article, I will explain about persisting the state information, when changes in configuration occur.