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： 

001package net.androgames.blog.sample.livewallpaper;

002  

003import android.content.SharedPreferences;

004import android.service.wallpaper.WallpaperService;

005import android.view.MotionEvent;

006import 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 */

013public 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： 

001package net.androgames.blog.sample.livewallpaper;

002  

003import android.content.Context;

004import android.graphics.Canvas;

005import android.view.MotionEvent;

006import 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 */

013public 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;

057        synchronized(this) {

058            this.notify();

059        }

060    }

061  

062    /**

063     * Stop the live wallpaper animation

064     */

065    public void stopPainting() {

066        this.run = false;

067        synchronized(this) {

068            this.notify();

069        }

070    }

071  

072    @Override

073    public void run() {

074        this.run = true;

075        Canvas c = null;

076        while (run) {

077            try {

078                c = this.surfaceHolder.lockCanvas(null);

079                synchronized (this.surfaceHolder) {

080                    currentTime = System.currentTimeMillis();

081                    updatePhysics();

082                    doDraw(c);

083                    previousTime = currentTime;

084                }

085            } finally {

086                if (c != null) {

087                    this.surfaceHolder.unlockCanvasAndPost(c);

088                }

089            }

090            // pause if no need to animate

091            synchronized (this) {

092                if (wait) {

093                    try {

094                        wait();

095                    } catch (Exception e) {}

096                }

097            }

098        }

099    }

100  

101    /**

102     * Invoke when the surface dimension change

103     */

104    public void setSurfaceSize(int width, int height) {

105        this.width = width;

106        this.height = height;

107        synchronized(this) {

108            this.notify();

109        }

110    }

111  

112    /**

113     * Invoke while the screen is touched

114     */

115    public void doTouchEvent(MotionEvent event) {

116        // handle the event here

117        // if there is something to animate

118        // then wake up

119        this.wait = false;

120        synchronized(this) {

121            notify();

122        }

123    }

124  

125    /**

126     * Do the actual drawing stuff

127     */

128    private void doDraw(Canvas canvas) {}

129  

130    /**

131     * Update the animation, sprites or whatever.

132     * If there is nothing to animate set the wait

133     * attribute of the thread to true

134     */

135    private void updatePhysics() {

136        // if nothing was updated :

137        // this.wait = true;

138    }

139  

140}

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。