Android动态壁纸的制作教程

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： 

01 <service
02     android:name="LiveWallpaperService"
03     android:enabled="true"
04     android:icon="@drawable/icon"
05     android:label="@string/app_name"
06     android:permission="android.permission.BIND_WALLPAPER">
07     <intent-filter android:priority="1" >
08         <action android:name="android.service.wallpaper.WallpaperService" />
09     </intent-filter>
10     <meta-data
11       android:name="android.service.wallpaper"
12       android:resource="@xml/wallpaper" />
13 </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。 

1 <?xml version="1.0" encoding="UTF-8"?>
2 <wallpaper
3     xmlns:android="http://schemas.android.com/apk/res/android"
4     android:thumbnail="@drawable/thumbnail"
5     android:description="@string/description"
6     android:settingsActivity="PreferenceActivity"/>

再创建一个xml的属性文件 attrs.xml ，代码如下： 

01 <declare-styleable name="Wallpaper">
02     <!-- Component name of an activity that allows the user to modify
03          the current settings for this wallpaper. -->
04     <attr name="settingsActivity" />
05
06     <!-- Reference to a the wallpaper's thumbnail bitmap. -->
07     <attr name="thumbnail" format="reference" />
08
09     <!-- Name of the author of this component, e.g. Google. -->
10     <attr name="author" format="reference" />
11
12     <!-- Short description of the component's purpose or behavior. -->
13     <attr name="description" />
14 </declare-styleable>

动态壁纸的服务代码如下： 

001 package net.androgames.blog.sample.livewallpaper;
002
003 import android.content.SharedPreferences;
004 import android.service.wallpaper.WallpaperService;
005 import android.view.MotionEvent;
006 import android.view.SurfaceHolder;
007
008 /**
009  * Android Live Wallpaper Archetype
010  * @author antoine vianey
011  * under GPL v3 : http://www.gnu.org/licenses/gpl-3.0.html
012  */
013 public class LiveWallpaperService extends WallpaperService {
014
015     @Override
016     public Engine onCreateEngine() {
017         return new SampleEngine();
018     }
019
020     @Override
021     public void onCreate() {
022         super.onCreate();
023     }
024
025     @Override
026     public void onDestroy() {
027         super.onDestroy();
028     }
029
030     public class SampleEngine extends Engine {
031
032         private LiveWallpaperPainting painting;
033
034         SampleEngine() {
035             SurfaceHolder holder = getSurfaceHolder();
036             painting = new LiveWallpaperPainting(holder,
037                 getApplicationContext());
038         }
039
040         @Override
041         public void onCreate(SurfaceHolder surfaceHolder) {
042             super.onCreate(surfaceHolder);
043             // register listeners and callbacks here
044             setTouchEventsEnabled(true);
045         }
046
047         @Override
048         public void onDestroy() {
049             super.onDestroy();
050             // remove listeners and callbacks here
051             painting.stopPainting();
052         }
053
054         @Override
055         public void onVisibilityChanged(boolean visible) {
056             if (visible) {
057                 // register listeners and callbacks here
058                 painting.resumePainting();
059             } else {
060                 // remove listeners and callbacks here
061                 painting.pausePainting();
062             }
063         }
064
065         @Override
066         public void onSurfaceChanged(SurfaceHolder holder, int format,
067                 int width, int height) {
068             super.onSurfaceChanged(holder, format, width, height);
069             painting.setSurfaceSize(width, height);
070         }
071
072         @Override
073         public void onSurfaceCreated(SurfaceHolder holder) {
074             super.onSurfaceCreated(holder);
075             // start painting
076             painting.start();
077         }
078
079         @Override
080         public void onSurfaceDestroyed(SurfaceHolder holder) {
081             super.onSurfaceDestroyed(holder);
082             boolean retry = true;
083             painting.stopPainting();
084             while (retry) {
085                 try {
086                     painting.join();
087                     retry = false;
088                 } catch (InterruptedException e) {}
089             }
090         }
091
092         @Override
093         public void onOffsetsChanged(float xOffset, float yOffset,
094                 float xStep, float yStep, int xPixels, int yPixels) {
095         }
096
097         @Override
098         public void onTouchEvent(MotionEvent event) {
099             super.onTouchEvent(event);
100             painting.doTouchEvent(event);
101         }
102
103     }
104
105 }

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： 

001 package net.androgames.blog.sample.livewallpaper;
002
003 import android.content.Context;
004 import android.graphics.Canvas;
005 import android.view.MotionEvent;
006 import android.view.SurfaceHolder;
007
008 /**
009  * Android Live Wallpaper painting thread Archetype
010  * @author antoine vianey
011  * GPL v3 : http://www.gnu.org/licenses/gpl-3.0.html
012  */
013 public class LiveWallpaperPainting extends Thread {
014
015     /** Reference to the View and the context */
016     private SurfaceHolder surfaceHolder;
017     private Context context;
018
019     /** State */
020     private boolean wait;
021     private boolean run;
022
023     /** Dimensions */
024     private int width;
025     private int height;
026
027     /** Time tracking */
028     private long previousTime;
029     private long currentTime;
030
031     public LiveWallpaperPainting(SurfaceHolder surfaceHolder,
032             Context context) {
033         // keep a reference of the context and the surface
034         // the context is needed if you want to inflate
035         // some resources from your livewallpaper .apk
036         this.surfaceHolder = surfaceHolder;
037         this.context = context;
038         // don't animate until surface is created and displayed
039         this.wait = true;
040     }
041
042     /**
043      * Pauses the live wallpaper animation
044      */
045     public void pausePainting() {
046         this.wait = true;
047         synchronized(this) {
048             this.notify();
049         }
050     }
051
052     /**
053      * Resume the live wallpaper animation
054      */
055     public void resumePainting() {
056         this.wait = false;