The following tutorial assumes that you have already basic knowledge in Android development. Please check the Android development tutorial to learn the basics.

Create a new project called de.vogella.android.wallpaper. Do not create an activity.

Create the /res/xml folder and create the mywallpaper.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<wallpaper 
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:thumbnail="@drawable/icon"
  android:description="@string/wallpaper_description"  
  android:settingsActivity="de.vogella.android.wallpaper.MyPreferencesActivity"/> 

This file contains a description of your wallpaper and a preview graphic. You can also enter a link to an activity which allow to configure the wallpaper. This resource file will be linked to from the AndroidManifest.xml. You could also include the "android:thumbnail attribute" which would point to a drawable which gives a smaller image of the running wallpaper.

Change your AndroidManifest.xml to the following to define your MyWallpaperService service. Also define the uses-feature.

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

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <service
            android:name="MyWallpaperService"
            android:enabled="true"
            android:label="Wallpaper Example "
            android:permission="android.permission.BIND_WALLPAPER" >
            <intent-filter>
                <action android:name="android.service.wallpaper.WallpaperService" >
                </action>
            </intent-filter>

            <meta-data
                android:name="android.service.wallpaper"
                android:resource="@xml/mywallpaper" >
            </meta-data>
        </service>

        <activity
            android:name=".MyPreferencesActivity"
            android:exported="true"
            android:label="@string/app_name"
            android:theme="@android:style/Theme.Light.WallpaperSettings" >
        </activity>
        <activity
            android:name=".SetWallpaperActivity"
            android:label="@string/app_name"
            android:theme="@android:style/Theme.Light.WallpaperSettings" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

    <uses-sdk android:minSdkVersion="10" />

    <uses-feature
        android:name="android.software.live_wallpaper"
        android:required="true" >
    </uses-feature>

</manifest> 

We create the MyPoint class to save the elements we have drawn.

package de.vogella.android.wallpaper;

public class MyPoint {
  String text;
  private int x;
  private int y;

  public MyPoint(String text, int x, int y) {
    this.text = text;
    this.x = x;
    this.y = y;
  }
} 

Create a new activity. Create the prefs.xml preference file in the res/xml folder.

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
  <CheckBoxPreference android:key="touch"
    android:title="Enable Touch"></CheckBoxPreference>
  <EditTextPreference android:key="numberOfCircles"
    android:title="Number of Circles"></EditTextPreference>
</PreferenceScreen> 

Create a new activity called MyPreferencesActivity and the following class.

package de.vogella.android.wallpaper;

import android.os.Bundle;
import android.preference.Preference;
import android.preference.Preference.OnPreferenceChangeListener;
import android.preference.PreferenceActivity;
import android.widget.Toast;

public class MyPreferencesActivity extends PreferenceActivity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    addPreferencesFromResource(R.xml.prefs);

    // We want to add a validator to the number of circles so that it only
    // accepts numbers
    Preference circlePreference = getPreferenceScreen().findPreference("numberOfCircles");

    // Add the validator
    circlePreference.setOnPreferenceChangeListener(numberCheckListener);
  }

  
/**
   * Checks that a preference is a valid numerical value
   */
  Preference.OnPreferenceChangeListener numberCheckListener = new OnPreferenceChangeListener() {

    @Override
    public boolean onPreferenceChange(Preference preference, Object newValue) {
      // Check that the string is an integer
      if (newValue != null && newValue.toString().length() > 0
          && newValue.toString().matches("\\d*")) {
        return true;
      }
      // If now create a message to the user
      Toast.makeText(MyPreferencesActivity.this, "Invalid Input",
          Toast.LENGTH_SHORT).show();
      return false;
    }
  };

} 

Create the following coding for the Wallpaper service.

package de.vogella.android.wallpaper;

import java.util.ArrayList;
import java.util.List;

import android.content.SharedPreferences;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Handler;
import android.preference.PreferenceManager;
import android.service.wallpaper.WallpaperService;
import android.view.MotionEvent;
import android.view.SurfaceHolder;

public class MyWallpaperService extends WallpaperService {

  @Override
  public Engine onCreateEngine() {
    return new MyWallpaperEngine();
  }

  private class MyWallpaperEngine extends Engine {
    private final Handler handler = new Handler();
    private final Runnable drawRunner = new Runnable() {
      @Override
      public void run() {
        draw();
      }

    };
    private List<MyPoint> circles;
    private Paint paint = new Paint();
    private int width;
    int height;
    private boolean visible = true;
    private int maxNumber;
    private boolean touchEnabled;

    public MyWallpaperEngine() {
      SharedPreferences prefs = PreferenceManager
          .getDefaultSharedPreferences(MyWallpaperService.this);
      maxNumber = Integer
          .valueOf(prefs.getString("numberOfCircles", "4"));
      touchEnabled = prefs.getBoolean("touch", false);
      circles = new ArrayList<MyPoint>();
      paint.setAntiAlias(true);
      paint.setColor(Color.WHITE);
      paint.setStyle(Paint.Style.STROKE);
      paint.setStrokeJoin(Paint.Join.ROUND);
      paint.setStrokeWidth(10f);
      handler.post(drawRunner);
    }

    @Override
    public void onVisibilityChanged(boolean visible) {
      this.visible = visible;
      if (visible) {
        handler.post(drawRunner);
      } else {
        handler.removeCallbacks(drawRunner);
      }
    }

    

} 

@Override
    public void onSurfaceDestroyed(SurfaceHolder holder) {
      super.onSurfaceDestroyed(holder);
      this.visible = false;
      handler.removeCallbacks(drawRunner);
    }

    @Override
    public void onSurfaceChanged(SurfaceHolder holder, int format,
        int width, int height) {
      this.width = width;
      this.height = height;
      super.onSurfaceChanged(holder, format, width, height);
    }

    @Override
    public void onTouchEvent(MotionEvent event) {
      if (touchEnabled) {

        float x = event.getX();
        float y = event.getY();
        SurfaceHolder holder = getSurfaceHolder();
        Canvas canvas = null;
        try {
          canvas = holder.lockCanvas();
          if (canvas != null) {
            canvas.drawColor(Color.BLACK);
            circles.clear();
            circles.add(new MyPoint(String.valueOf(circles.size() + 1), x, y));
            drawCircles(canvas, circles);

          }
        } finally {
          if (canvas != null)
            holder.unlockCanvasAndPost(canvas);
        }
        super.onTouchEvent(event);
      }
    }

    private void draw() {
      SurfaceHolder holder = getSurfaceHolder();
      Canvas canvas = null;
      try {
        canvas = holder.lockCanvas();
        if (canvas != null) {
          if (circles.size() >= maxNumber) {
            circles.clear();
          }
          int x = (int) (width * Math.random());
          int y = (int) (height * Math.random());
          circles.add(new MyPoint(String.valueOf(circles.size() + 1),
              x, y));
          drawCircles(canvas, circles);
        }
      } finally {
        if (canvas != null)
          holder.unlockCanvasAndPost(canvas);
      }
      handler.removeCallbacks(drawRunner);
      if (visible) {
        handler.postDelayed(drawRunner, 5000);
      }
    }

    // Surface view requires that all elements are drawn completely
    private void drawCircles(Canvas canvas, List<MyPoint> circles) {
      canvas.drawColor(Color.BLACK);
      for (MyPoint point : circles) {
        canvas.drawCircle(point.x, point.y, 20.0f, paint);
      }
    }
  } 

Create the following Activity which should use a layout with one Button included. This Button should use the onClick property to point to the onClick method.

package de.vogella.android.wallpaper;

import android.app.Activity;
import android.app.WallpaperManager;
import android.content.ComponentName;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;

public class SetWallpaperActivity extends Activity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
  }

  public void onClick(View view) {
    Intent intent = new Intent(WallpaperManager.ACTION_CHANGE_LIVE_WALLPAPER);
    intent.putExtra(WallpaperManager.EXTRA_LIVE_WALLPAPER_COMPONENT,
        new ComponentName(this, MyWallpaperService.class));
    startActivity(intent);
  }
} 

If you start your application your application should allow to set the wallpaper. Your background should look similar to the following screenshot. If you have Touch enabled via the preferences you can click on the screen to remove the existing circles, also via the settings you can define the number of circles which should be displayed.

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