Here is source code of the Program to create an Activity to set the Wallpaper of your Decive. The program is successfully compiled and run on a Windows system using Eclipse Ide. The program output is also shown below.

Main Activity


package com.example.backgroundapp;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button =(Button) findViewById(R.id.button1);

button.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent("com.example.backgroundapp.bakapp"));
}
});
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}

}
Backapp Activity


package com.example.backgroundapp;

import java.io.IOException;
import java.io.InputStream;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

public class bakapp extends Activity implements OnClickListener {
ImageView display;
int tophone;

@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);

// to our activity to cover the whole screen
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);

setContentView(R.layout.back);
Button but = (Button) findViewById(R.id.setwallpaper);
tophone = R.drawable.image4;
but.setOnClickListener(this);
display = (ImageView) findViewById(R.id.ivdisplay);
ImageView image1 = (ImageView) findViewById(R.id.IVimage1);
ImageView image2 = (ImageView) findViewById(R.id.IVimage2);
ImageView image3 = (ImageView) findViewById(R.id.IVimage3);
ImageView image4 = (ImageView) findViewById(R.id.image4);
ImageView image5 = (ImageView) findViewById(R.id.IVimage5);

image1.setOnClickListener(this);
image2.setOnClickListener(this);
image3.setOnClickListener(this);
image4.setOnClickListener(this);
image5.setOnClickListener(this);

}

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Toast var;
switch (v.getId()) {
case R.id.IVimage1:
display.setImageResource(R.drawable.image4);
var = Toast.makeText(bakapp.this, "image changed",
Toast.LENGTH_SHORT);

var.show();

tophone = R.drawable.image4;
break;
case R.id.IVimage2:
display.setImageResource(R.drawable.image5);
var = Toast.makeText(bakapp.this, "image changed",
Toast.LENGTH_SHORT);

var.show();

tophone = R.drawable.image5;
break;
case R.id.IVimage3:
display.setImageResource(R.drawable.image6);
var = Toast.makeText(bakapp.this, "image changed",
Toast.LENGTH_SHORT);

var.show();

tophone = R.drawable.image6;
break;
case R.id.image4:
display.setImageResource(R.drawable.image7);
var = Toast.makeText(bakapp.this, "image changed",
Toast.LENGTH_SHORT);

var.show();

tophone = R.drawable.image7;
break;
case R.id.IVimage5:
display.setImageResource(R.drawable.image8);
var = Toast.makeText(bakapp.this, "image changed",
Toast.LENGTH_SHORT);

var.show();

tophone = R.drawable.image8;
break;
case R.id.setwallpaper:
// to set a background we need to use bitmap
InputStream is = getResources().openRawResource(tophone);
// to phone is a variable that is updated everytime we click on an
// ImageView to that imageview resource and by clicking the button
// we set the phone background to that image.
Bitmap bm = BitmapFactory.decodeStream(is);
// decode inputstream is
try {
getApplicationContext().setWallpaper(bm);
// to set the wallpaper of the phone background we need to ask
// permission from the user so add permission of background from
// manifest file

} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
var = Toast.makeText(bakapp.this, "Wallpaper image changed",
Toast.LENGTH_SHORT);

var.show();

break;
}
}

}

Xml

Main


<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >

<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Application to Change background picture of device"
android:textSize="30dp" />

<Button
android:id="@+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_marginBottom="96dp"
android:text="Click to launch" />

</RelativeLayout>


Backapp


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ImageView
android:id="@+id/ivdisplay"
android:layout_width="200dp"
android:layout_height="200dp"
android:layout_gravity="center"
android:src="@drawable/image4" />
"
<Button
android:id="@+id/setwallpaper"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="set image background" >
</Button>

<HorizontalScrollView
android:layout_width="200dp"
android:layout_height="wrap_content"
android:layout_gravity="center" >

<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">

<ImageView
android:id="@+id/IVimage1"
android:layout_width="125dp"
android:layout_height="125dp"
android:padding="15dp"
android:src="@drawable/image4" />

<ImageView
android:id="@+id/IVimage2"
android:layout_width="125dp"
android:layout_height="125dp"
android:padding="15dp"
android:src="@drawable/image5" />

<ImageView
android:id="@+id/IVimage3"
android:layout_width="125dp"
android:layout_height="125dp"
android:padding="15dp"
android:src="@drawable/image6" />

<ImageView
android:id="@+id/image4"
android:layout_width="125dp"
android:layout_height="125dp"
android:padding="15dp"
android:src="@drawable/image7" />

<ImageView
android:id="@+id/IVimage5"
android:layout_width="125dp"
android:layout_height="125dp"
android:padding="15dp"
android:src="@drawable/image8" />
</LinearLayout>
</HorizontalScrollView>

</LinearLayout>

AndroidManifest

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

<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<uses-permission android:name="android.permission.SET_WALLPAPER"/>

<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.backgroundapp.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.backgroundapp.bakapp"
android:label="@string/app_name"
android:screenOrientation="portrait">
<intent-filter>
<action android:name="com.example.backgroundapp.bakapp" />

<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>

</manifest>