动态壁纸是在Android 2.1新增的一个功能。动态壁纸可以添加到Android的桌面，具有交互式的动画背景效果。在本教程中，我们将教会你如何去制作一个交互式的动态壁纸。
动态壁纸是一个Android应用程序，包括一个服务(WallpaperService)。该服务必须包括一个引擎(WallpaperService.Engine)。该引擎是连接用户、桌面、系统之间的桥梁。它也可以绘制桌面壁纸。
首先，必须由内在的Engine类创建一个WallpaperService类。该服务必须在AndroidManifest.xml中声明为"android.service.wallpaper.WallpaperService"，这样它才会作为动态壁纸被手机识别。而且还要在服务配置中附加"android.permission.BIND_WALLPAPER"的权限许可：
<service
android:name="LiveWallpaperService"
android:enabled="true"
android:icon="@drawable/icon"
android:label="@string/app_name"
android:permission="android.permission.BIND_WALLPAPER">
<intent-filter android:priority="1" >
<action android:name="android.service.wallpaper.WallpaperService" />
</intent-filter>
<meta-data
android:name="android.service.wallpaper"
android:resource="@xml/wallpaper" />
</service>
创建一个XML文件，放置在应用程序目录下的/res/xml/中。它用来描述你的动态壁纸。
<?xml version="1.0" encoding="UTF-8"?>
<wallpaper
xmlns:android="http://schemas.android.com/apk/res/android"
android:thumbnail="@drawable/thumbnail"
android:description="@string/description"
android:settingsActivity="PreferenceActivity"/>
再创建一个xml的属性文件 attrs.xml ，代码如下：
<declare-styleable name="Wallpaper">
<!-- Component name of an activity that allows the user to modify
the current settings for this wallpaper. -->
<attr name="settingsActivity" />
<!-- Reference to a the wallpaper\'s thumbnail bitmap. -->
<attr name="thumbnail" format="reference" />
<!-- Name of the author of this component, e.g. Google. -->
<attr name="author" format="reference" />
<!-- Short description of the component\'s purpose or behavior. -->
<attr name="description" />
</declare-styleable>
动态壁纸的服务代码如下
import android.content.SharedPreferences;
import android.service.wallpaper.WallpaperService;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
/**
* Android Live Wallpaper Archetype
* @author antoine vianey
* under GPL v3 : http://www.gnu.org/licenses/gpl-3.0.html
*/
public class LiveWallpaperService extends WallpaperService {
@Override
public Engine onCreateEngine() {
return new SampleEngine();
}
@Override
public void onCreate() {
super.onCreate();
}
@Override
public void onDestroy() {
super.onDestroy();
}
public class SampleEngine extends Engine {
private LiveWallpaperPainting painting;
SampleEngine() {
SurfaceHolder holder = getSurfaceHolder();
painting = new LiveWallpaperPainting(holder,
getApplicationContext());
}
@Override
public void onCreate(SurfaceHolder surfaceHolder) {
super.onCreate(surfaceHolder);
// register listeners and callbacks here
setTouchEventsEnabled(true);
}
@Override
public void onDestroy() {
super.onDestroy();
// remove listeners and callbacks here
painting.stopPainting();
}
@Override
public void onVisibilityChanged(boolean visible) {
if (visible) {
// register listeners and callbacks here
painting.resumePainting();
} else {
// remove listeners and callbacks here
painting.pausePainting();
}
}
@Override
public void onSurfaceChanged(SurfaceHolder holder, int format,
int width, int height) {
super.onSurfaceChanged(holder, format, width, height);
painting.setSurfaceSize(width, height);
}
@Override
public void onSurfaceCreated(SurfaceHolder holder) {
super.onSurfaceCreated(holder);
// start painting
painting.start();
}
@Override
public void onSurfaceDestroyed(SurfaceHolder holder) {
super.onSurfaceDestroyed(holder);
boolean retry = true;
painting.stopPainting();
while (retry) {
try {
painting.join();
retry = false;
} catch (InterruptedException e) {}
}
}
@Override
public void onOffsetsChanged(float xOffset, float yOffset,
float xStep, float yStep, int xPixels, int yPixels) {
}
@Override
public void onTouchEvent(MotionEvent event) {
super.onTouchEvent(event);
painting.doTouchEvent(event);
}
}
}
当壁纸的显示、状态或大小变化是，会调用Engine的onCreate, onDestroy, onVisibilityChanged, onSurfaceChanged, onSurfaceCreated 和 onSurfaceDestroyed方法。有了这些方法，动态壁纸才能展现出动画效果。而通过设置setTouchEventsEnabled（true），并且调用onTouchEvent（MotionEvent event）方法，来激活触摸事件。
我们在绘画墙纸的时候，也会使用一个单独的绘画线程
import android.content.Context;
import android.graphics.Canvas;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
/**
* Android Live Wallpaper painting thread Archetype
* @author antoine vianey
* GPL v3 : http://www.gnu.org/licenses/gpl-3.0.html
*/
public class LiveWallpaperPainting extends Thread {
/** Reference to the View and the context */
private SurfaceHolder surfaceHolder;
private Context context;
/** State */
private boolean wait;
private boolean run;
/** Dimensions */
private int width;
private int height;
/** Time tracking */
private long previousTime;
private long currentTime;
public LiveWallpaperPainting(SurfaceHolder surfaceHolder,
Context context) {
// keep a reference of the context and the surface
// the context is needed if you want to inflate
// some resources from your livewallpaper .apk
this.surfaceHolder = surfaceHolder;
this.context = context;
// don\'t animate until surface is created and displayed
this.wait = true;
}
/**
* Pauses the live wallpaper animation
*/
public void pausePainting() {
this.wait = true;
synchronized(this) {
this.notify();
}
}
/**
* Resume the live wallpaper animation
*/
public void resumePainting() {
this.wait = false;
synchronized(this) {
this.notify();
}
}
/**
* Stop the live wallpaper animation
*/
public void stopPainting() {
this.run = false;
synchronized(this) {
this.notify();
}
}
@Override
public void run() {
this.run = true;
Canvas c = null;
while (run) {
try {
c = this.surfaceHolder.lockCanvas(null);
synchronized (this.surfaceHolder) {
currentTime = System.currentTimeMillis();
updatePhysics();
doDraw(c);
previousTime = currentTime;
}
} finally {
if (c != null) {
this.surfaceHolder.unlockCanvasAndPost(c);
}
}
// pause if no need to animate
synchronized (this) {
if (wait) {
try {
wait();
} catch (Exception e) {}
}
}
}
}
/**
* Invoke when the surface dimension change
*/
public void setSurfaceSize(int width, int height) {
this.width = width;
this.height = height;
synchronized(this) {
this.notify();
}
}
/**
* Invoke while the screen is touched
*/
public void doTouchEvent(MotionEvent event) {
// handle the event here
// if there is something to animate
// then wake up
this.wait = false;
synchronized(this) {
notify();
}
}
/**
* Do the actual drawing stuff
*/
private void doDraw(Canvas canvas) {}
/**
* Update the animation, sprites or whatever.
* If there is nothing to animate set the wait
* attribute of the thread to true
*/
private void updatePhysics() {
// if nothing was updated :
// this.wait = true;
}
}
如果桌面壁纸是可见状态下，系统服务通知有新的东西，这个类会优先把它绘制在画布上。如果没有动画了，updatePhysics会通知线程去等待。通常SurfaceView在有两个画布交替绘制的时候，会在画布上绘制上一次......
如果要让你的动态墙纸有配置功能，只要创建一个PreferenceActivity，并将它在wallpaper.xml文件中声明。同时让SharedPreference对象可以找到你的配置选项。
教程就写到这里，如果还有什么不懂，你可以通过Eclipse来浏览完整的源代码：SampleLiveWallpaper
