Handling Runtime Changes in Android

Introduction

 

In this article, you will learn about How to Runtime changes in Android.

 

You have seen that every android device has a functionality to change the orientation of the screen at runtime. So when the device changes its orientation the activity will be restarted by calling all its methods again. On orientation changes first, the activity will be destroyed and again created.

 

When the Activity is destroyed system calls onPause(), onStop(), and onDestroy() method simultaneously. And now to create activity system calls onCreate(), onStop(), and onResume() simultaneously.

 

First, let's see how you handle the runtime changes in Android

 

In this I am using a count down timer to show you, The timer will not be affected when the screen orientation changes. I have already explained that the activity restarted when the device changes its orientation. So to overcome this we write the element Android Manifest.xml file

android:configChanges="orientation|screenSize|keyboardHidden". In java class file we will override the onConfigurationChanged().

 

onConfiguration change() - This method is called by the system when the device configuration changes while your activity is running

 

Now when configuration changes the activity will not be restart. So when the device changes its orientation the onConfigurationChanged() method will be called.

 

Step 1

 

Create a project like this

 

Step 2

 

Create an Xml file and write this

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:background="#ff998765"
   android:orientation="vertical" >

   <TextView
       android:id="@+id/textView"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_centerHorizontal="true"
       android:layout_centerVertical="true"
       android:paddingRight="10dip"
       android:textSize="50dp" />

   <Button
       android:id="@+id/button"
       android:layout_width="fill_parent"
       android:layout_height="wrap_content"
       android:layout_alignParentBottom="true"
       android:layout_alignParentLeft="true"
       android:text="Start" />

</RelativeLayout>

Step 3

 

In this, I have created a timer inside activity that is started on button click. So when you start the timer in portrait mode the timer start counting. When you change the device orientation the timer will start from that count.

 

Create a java class file and write this

package com.example.screenorientation;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.app.Activity;
import android.content.res.Configuration;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.RadioButton;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity
{
 private CountDownTimer countDownTimer;
 private boolean timerStarted = false;
 private Button buttonStart;
 public TextView textView;
 private final long startTime = 100 * 100;
 private final long interval = 1 * 100;
 @Override
 protected void onCreate(Bundle savedInstanceState)
 {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  Log.d("cycle", "onCreate wiil be invoke");
  buttonStart = (Button) this.findViewById(R.id.button);
  textView = (TextView) this.findViewById(R.id.textView);
  countDownTimer = new CountDownTimerActivity(startTime, interval);
  textView.setText(textView.getText() + String.valueOf(startTime / 1000));
  buttonStart.setOnClickListener(new OnClickListener()
  {
   @Override
   public void onClick(View arg0)
   {
    if (!timerStarted)
    {
     countDownTimer.start();
     timerStarted = true;
     buttonStart.setText("STOP");
    }
    else
    {
     countDownTimer.cancel();
     timerStarted = false;
     buttonStart.setText("RESTART");
    }
   }
  });
 }
 public class CountDownTimerActivity extends CountDownTimer
 {
  public CountDownTimerActivity(long startTime, long interval)
  {
   super(startTime, interval);
  }
  @Override
  public void onFinish()
  {
   textView.setText("Time's up!");
  }
  @Override
  public void onTick(long millisUntilFinished)
  {
   textView.setText("" + millisUntilFinished / 1000);
  }
 }
 @Override
 protected void onStart()
 {
  super.onStart();
  Log.d("cycle", "onStart wiil be invoked");
 }
 @Override
 protected void onResume()
 {
  super.onResume();
  Log.d("cycle", "onResume wiil be invoked");
 }
 @Override
 protected void onPause()
 {
  super.onPause();
  Log.d("cycle", "onPause wiil be invoked");
 }
 @Override
 protected void onStop()
 {
  super.onStop();
  Log.d("cycle", "onStop wiil be invoked");
 }
 @Override
 protected void onRestart()
 {
  super.onRestart();
  Log.d("cycle", "onRestart wiil be invoked");
 }
 @Override
 protected void onDestroy()
 {
  super.onDestroy();
  Log.d("cycle", "onDestroy wiil be invoked");
 }
 @Override
 public void onConfigurationChanged(Configuration newConfig)
 {
  super.onConfigurationChanged(newConfig);
  if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) {} else if (newConfig.orientation == Configuration.ORIENTATION_PORTRAIT) {}
 }
 @Override
 public boolean onCreateOptionsMenu(Menu menu)
 {
  getMenuInflater().inflate(R.menu.main, menu);
  return true;
 }
}

Step 4

 

Android Manifest.xml file

 

In Android Manifest .xml file you will write the configuration element in <activity>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.screenorientation"
   android:versionCode="1"
   android:versionName="1.0">

   <uses-sdk
       android:minSdkVersion="8"
       android:targetSdkVersion="18"/>

   <application
       android:allowBackup="true"
       android:icon="@drawable/ic_launcher"
       android:label="@string/app_name"
       android:theme="@style/AppTheme">
       <activity
           android:name="com.example.screenorientation.MainActivity"
             android:configChanges="orientation|screenSize|keyboardHidden"
           android:label="@string/app_name">
           <intent-filter>
               <action android:name="android.intent.action.MAIN" />
               <category android:name="android.intent.category.LAUNCHER" />
           </intent-filter>
       </activity>
   </application>
</manifest>

Step 5

 

After running of activity onCreate(), onStart, onResume() called simultaneuosly

 

 

When the Device orientation changes no methods called which means the activity not restarted