动态壁纸探究

随着

三星

Oscar的上市，流畅的操作，华丽的界面，

OPhone

2.0的不俗表现不禁让人眼前一亮。作为OPhone 2.0一个新特性，动态壁纸(Live Wallpapers)为用户带来了更炫体验。本文主要通过一个完整的时间壁纸（TimeWall）为大家介绍如何开发 Live Wallpapers。还没开发环境？赶紧去下载OPhone

SDK

2.0吧！

1、 Live Wallpapers是什么？

在oscar上有一个动态壁纸叫“天空草地”，用过一段时间，可以发现，随着时间的变化，壁纸的天空就会由蓝蓝青天变成繁星满天。看看效果：

为什么壁纸还有这么神奇的变化，这中间到底是什么在起作用？其实，一个Live Wallpaper就是一个apk！也就是说，动态壁纸的实质是一个apk在后台不断地重绘壁纸，所以我们可以让小草长高，小鸟飞翔。

来看一下AndoridManifest.xml：

<?xml version=”1.0″ encoding=”utf-8″?><br /> <!–<br /> /*<br /> **<br /> ** Copyright 2009, The Android Open Source Project<br /> **<br /> ** Licensed under the Apache License, Version 2.0 (the “License”);<br /> ** you may not use this file except in compliance with the License.<br /> ** You may obtain a copy of the License at<br /> **<br /> ** http://www.apache.org/licenses/LICENSE-2.0<br /> **<br /> ** Unless required by applicable law or agreed to in writing, software<br /> ** distributed under the License is distributed on an “AS IS” BASIS,<br /> ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<br /> ** See the License for the specific language governing permissions and<br /> ** limitations under the License.<br /> */<br /> –><br /> <manifest<br /> xmlns:android=”http://schemas.android.com/apk/res/android”<br /> package=”com.example.android.livecubes”><br /> <uses-sdk android:minSdkVersion=”7″ /><br /> <uses-feature android:name=”android.software.live_wallpaper” /><br /> <application<br /> android:label=”@string/wallpapers”<br /> android:icon=”@drawable/ic_launcher_wallpaper”><br /> <service<br /> android:label=”@string/wallpaper_cube1″<br /> android:name=”.cube1.CubeWallpaper1″<br /> android:permission=”android.permission.BIND_WALLPAPER”><br /> <intent-filter><br /> <action android:name=”android.service.wallpaper.WallpaperService” /><br /> </intent-filter><br /> <meta-data android:name=”android.service.wallpaper” android:resource=”@xml/cube1″ /><br /> </service><br /> <service<br /> android:label=”@string/wallpaper_cube2″<br /> android:name=”.cube2.CubeWallpaper2″<br /> android:permission=”android.permission.BIND_WALLPAPER”><br /> <intent-filter><br /> <action android:name=”android.service.wallpaper.WallpaperService” /><br /> </intent-filter><br /> <meta-data android:name=”android.service.wallpaper” android:resource=”@xml/cube2″ /><br /> </service><br /> <activity<br /> android:label=”@string/cube2_settings”<br /> android:name=”.cube2.CubeWallpaper2Settings”<br /> android:theme=”@android:style/Theme.Light.WallpaperSettings”<br /> android:exported=”true”><br /> </activity><br /> <!–android:exported 是否可被其他程序调用 android:permission=”android.permission.BIND_WALLPAPER” 桌面服务绑定设置–><br /> </application><br /> </manifest><br />

原来如此简单，动态壁纸仅仅有一个service就够了。其中


Android

:permission=”android.permission.BIND_WALLPAPER”

是让该service有能设置为壁纸的权限，没有的话该壁纸只能被预览。

<uses-sdk android:minSdkVersion=”7″ />

告诉我们，如果你想开发一个live wallpaper，必须是OPhone 2.0或者更高的版本。当然这也需要手机硬件的支持。

2、怎样实现WallpaperService？

WallpaperService与其他的service唯一的不同就是，你必须要增加一个方法onCreateEngine()，它会返回一个 WallpaperService.Engine，这个engine才是负责绘制壁纸以及响应与用户交互事件的核心部件。这个service代码结构如下：

/*<br /> * Copyright (C) 2009 The Android Open Source Project<br /> *<br /> * Licensed under the Apache License, Version 2.0 (the “License”);<br /> * you may not use this file except in compliance with the License.<br /> * You may obtain a copy of the License at<br /> *<br /> * http://www.apache.org/licenses/LICENSE-2.0<br /> *<br /> * Unless required by applicable law or agreed to in writing, software<br /> * distributed under the License is distributed on an “AS IS” BASIS,<br /> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<br /> * See the License for the specific language governing permissions and<br /> * limitations under the License.<br /> */<br /> package com.example.android.livecubes.cube2;<br /> import android.content.SharedPreferences;<br /> import android.graphics.Canvas;<br /> import android.graphics.Paint;<br /> import android.graphics.Rect;<br /> import android.os.Handler;<br /> import android.os.SystemClock;<br /> import android.service.wallpaper.WallpaperService;<br /> import android.view.MotionEvent;<br /> import android.view.SurfaceHolder;<br /> /*<br /> * This animated wallpaper draws a rotating wireframe shape. It is similar to<br /> * example #1, but has a choice of 2 shapes, which are user selectable and<br /> * defined in resources instead of in code.<br /> */<br /> public class CubeWallpaper2 extends WallpaperService {<br /> public static final String SHARED_PREFS_NAME=”cube2settings”;<br /> static class ThreeDPoint {<br /> float x;<br /> float y;<br /> float z;<br /> }<br /> static class ThreeDLine {<br /> int startPoint;<br /> int endPoint;<br /> }<br /> @Override<br /> public void onCreate() {<br /> super.onCreate();<br /> }<br /> @Override<br /> public void onDestroy() {<br /> super.onDestroy();<br /> }<br /> @Override<br /> public Engine onCreateEngine() {<br /> return new CubeEngine();<br /> }<br /> class CubeEngine extends Engine<br /> implements SharedPreferences.OnSharedPreferenceChangeListener {<br /> private final Handler mHandler = new Handler();<br /> ThreeDPoint [] mOriginalPoints;<br /> ThreeDPoint [] mRotatedPoints;<br /> ThreeDLine [] mLines;<br /> private final Paint mPaint = new Paint();<br /> private float mOffset;<br /> private float mTouchX = -1;<br /> private float mTouchY = -1;<br /> private long mStartTime;<br /> private float mCenterX;<br /> private float mCenterY;<br /> private final Runnable mDrawCube = new Runnable() {<br /> public void run() {<br /> drawFrame();<br /> }<br /> };<br /> private boolean mVisible;<br /> private SharedPreferences mPrefs;<br /> CubeEngine() {<br /> // Create a Paint to draw the lines for our cube<br /> final Paint paint = mPaint;<br /> paint.setColor(0xffffffff);<br /> paint.setAntiAlias(true);<br /> paint.setStrokeWidth(2);<br /> paint.setStrokeCap(Paint.Cap.ROUND);<br /> paint.setStyle(Paint.Style.STROKE);<br /> mStartTime = SystemClock.elapsedRealtime();<br /> mPrefs = CubeWallpaper2.this.getSharedPreferences(SHARED_PREFS_NAME, 0);<br /> mPrefs.registerOnSharedPreferenceChangeListener(this);<br /> onSharedPreferenceChanged(mPrefs, null);<br /> }<br /> public void onSharedPreferenceChanged(SharedPreferences prefs, String key) {<br /> String shape = prefs.getString(“cube2_shape”, “cube”);<br /> // read the 3D model from the resource<br /> readModel(shape);<br /> }<br /> private void readModel(String prefix) {<br /> // Read the model definition in from a resource.<br /> // get the resource identifiers for the arrays for the selected shape<br /> int pid = getResources().getIdentifier(prefix + “points”, “array”, getPackageName());<br /> int lid = getResources().getIdentifier(prefix + “lines”, “array”, getPackageName());<br /> String [] p = getResources().getStringArray(pid);<br /> int numpoints = p.length;<br /> mOriginalPoints = new ThreeDPoint[numpoints];<br /> mRotatedPoints = new ThreeDPoint[numpoints];<br /> for (int i = 0; i < numpoints; i++) {<br /> mOriginalPoints[i] = new ThreeDPoint();<br /> mRotatedPoints[i] = new ThreeDPoint();<br /> String [] coord = p[i].split(” “);<br /> mOriginalPoints[i].x = Float.valueOf(coord[0]);<br /> mOriginalPoints[i].y = Float.valueOf(coord[1]);<br /> mOriginalPoints[i].z = Float.valueOf(coord[2]);<br /> }<br /> String [] l = getResources().getStringArray(lid);<br /> int numlines = l.length;<br /> mLines = new ThreeDLine[numlines];<br /> for (int i = 0; i < numlines; i++) {<br /> mLines[i] = new ThreeDLine();<br /> String [] idx = l[i].split(” “);<br /> mLines[i].startPoint = Integer.valueOf(idx[0]);<br /> mLines[i].endPoint = Integer.valueOf(idx[1]);<br /> }<br /> }<br /> @Override<br /> public void onCreate(SurfaceHolder surfaceHolder) {<br /> super.onCreate(surfaceHolder);<br /> setTouchEventsEnabled(true);<br /> }<br /> @Override<br /> public void onDestroy() {<br /> super.onDestroy();<br /> mHandler.removeCallbacks(mDrawCube);<br /> }<br /> @Override<br /> public void onVisibilityChanged(boolean visible) {<br /> mVisible = visible;<br /> if (visible) {<br /> drawFrame();<br /> } else {<br /> mHandler.removeCallbacks(mDrawCube);<br /> }<br /> }<br /> @Override<br /> public void onSurfaceChanged(SurfaceHolder holder, int format, int width, int height) {<br /> super.onSurfaceChanged(holder, format, width, height);<br /> // store the center of the surface, so we can draw the cube in the right spot<br /> mCenterX = width/2.0f;<br /> mCenterY = height/2.0f;<br /> drawFrame();<br /> }<br /> @Override<br /> public void onSurfaceCreated(SurfaceHolder holder) {<br /> super.onSurfaceCreated(holder);<br /> }<br /> @Override<br /> public void onSurfaceDestroyed(SurfaceHolder holder) {<br /> super.onSurfaceDestroyed(holder);<br /> mVisible = false;<br /> mHandler.removeCallbacks(mDrawCube);<br /> }<br /> @Override<br /> public void onOffsetsChanged(float xOffset, float yOffset,<br /> float xStep, float yStep, int xPixels, int yPixels) {<br /> mOffset = xOffset;<br /> drawFrame();<br /> }<br /> /*<br /> * Store the position of the touch event so we can use it for drawing later<br /> */<br /> @Override<br /> public void onTouchEvent(MotionEvent event) {<br /> if (event.getAction() == MotionEvent.ACTION_MOVE) {<br /> mTouchX = event.getX();<br /> mTouchY = event.getY();<br /> } else {<br /> mTouchX = -1;<br /> mTouchY = -1;<br /> }<br /> super.onTouchEvent(event);<br /> }<br /> /*<br /> * Draw one frame of the animation. This method gets called repeatedly<br /> * by posting a delayed Runnable. You can do any drawing you want in<br /> * here. This example draws a wireframe cube.<br /> */<br /> void drawFrame() {<br /> final SurfaceHolder holder = getSurfaceHolder();<br /> final Rect frame = holder.getSurfaceFrame();<br /> final int width = frame.width();<br /> final int height = frame.height();<br /> Canvas c = null;<br /> try {<br /> c = holder.lockCanvas();<br /> if (c != null) {<br /> // draw something<br /> drawCube(c);<br /> drawTouchPoint(c);<br /> }<br /> } finally {<br /> if (c != null) holder.unlockCanvasAndPost(c);<br /> }<br /> mHandler.removeCallbacks(mDrawCube);<br /> if (mVisible) {<br /> mHandler.postDelayed(mDrawCube, 1000 / 25);<br /> }<br /> }<br /> void drawCube(Canvas c) {<br /> c.save();<br /> c.translate(mCenterX, mCenterY);<br /> c.drawColor(0xff000000);<br /> long now = SystemClock.elapsedRealtime();<br /> float xrot = ((float)(now – mStartTime)) / 1000;<br /> float yrot = (0.5f – mOffset) * 2.0f;<br /> rotateAndProjectPoints(xrot, yrot);<br /> drawLines(c);<br /> c.restore();<br /> }<br /> void rotateAndProjectPoints(float xrot, float yrot) {<br /> int n = mOriginalPoints.length;<br /> for (int i = 0; i < n; i++) {<br /> // rotation around X-axis<br /> ThreeDPoint p = mOriginalPoints[i];<br /> float x = p.x;<br /> float y = p.y;<br /> float z = p.z;<br /> float newy = (float)(Math.sin(xrot) * z + Math.cos(xrot) * y);<br /> float newz = (float)(Math.cos(xrot) * z – Math.sin(xrot) * y);<br /> // rotation around Y-axis<br /> float newx = (float)(Math.sin(yrot) * newz + Math.cos(yrot) * x);<br /> newz = (float)(Math.cos(yrot) * newz – Math.sin(yrot) * x);<br /> // 3D-to-2D projection<br /> float screenX = newx / (4 – newz / 400);<br /> float screenY = newy / (4 – newz / 400);<br /> mRotatedPoints[i].x = screenX;<br /> mRotatedPoints[i].y = screenY;<br /> mRotatedPoints[i].z = 0;<br /> }<br /> }<br /> void drawLines(Canvas c) {<br /> int n = mLines.length;<br /> for (int i = 0; i < n; i++) {<br /> ThreeDLine l = mLines[i];<br /> ThreeDPoint start = mRotatedPoints[l.startPoint];<br /> ThreeDPoint end = mRotatedPoints[l.endPoint];<br /> c.drawLine(start.x, start.y, end.x, end.y, mPaint);<br /> }<br /> }<br /> void drawTouchPoint(Canvas c) {<br /> if (mTouchX >=0 && mTouchY >= 0) {<br /> c.drawCircle(mTouchX, mTouchY, 80, mPaint);<br /> }<br /> }<br /> }<br /> }<br />

/*<br /> * Copyright (C) 2009 Google Inc.<br /> *<br /> * Licensed under the Apache License, Version 2.0 (the “License”); you may not<br /> * use this file except in compliance with the License. You may obtain a copy of<br /> * the License at<br /> *<br /> * http://www.apache.org/licenses/LICENSE-2.0<br /> *<br /> * Unless required by applicable law or agreed to in writing, software<br /> * distributed under the License is distributed on an “AS IS” BASIS, WITHOUT<br /> * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the<br /> * License for the specific language governing permissions and limitations under<br /> * the License.<br /> */<br /> package com.example.android.livecubes.cube2;<br /> import com.example.android.livecubes.R;<br /> import android.content.SharedPreferences;<br /> import android.os.Bundle;<br /> import android.preference.PreferenceActivity;<br /> public class CubeWallpaper2Settings extends PreferenceActivity<br /> implements SharedPreferences.OnSharedPreferenceChangeListener {<br /> @Override<br /> protected void onCreate(Bundle icicle) {<br /> super.onCreate(icicle);<br /> getPreferenceManager().setSharedPreferencesName(<br /> CubeWallpaper2.SHARED_PREFS_NAME);<br /> addPreferencesFromResource(R.xml.cube2_settings);<br /> getPreferenceManager().getSharedPreferences().registerOnSharedPreferenceChangeListener(<br /> this);<br /> }<br /> @Override<br /> protected void onResume() {<br /> super.onResume();<br /> }<br /> @Override<br /> protected void onDestroy() {<br /> getPreferenceManager().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(<br /> this);<br /> super.onDestroy();<br /> }<br /> public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,<br /> String key) {<br /> }<br /> }<br />

类TimeEngine才是处理壁纸的核心类，我们会在类TimeEngine中加上自己的逻辑以完成壁纸的绘制、变化以及销毁。Engine的生命周期与大多数OPhone

应用程序

组件，比如activity类似，都是从onCreate()开始，在销毁时调用onDestory()方法。不同的是WallpaperService会提供一个surface用来绘制壁纸，所以在生命周期中多一个onSurfaceCreated与onSurfaceDestroyed的过程。下面是一个最简生命周期：

也就是说只要我们实现上面四个方法，一个基本的LiveWallpaper就可以完成了。让我们逐个看一下这几个方法的实现。

nCreate方法里，我们

setTouchEventsEnabled(true);

作用是使壁纸能响应touch event，默认是false。TimeWall会在用户点击屏幕的时候画一个十字架，所以我们需要设置其为true。

可以看到我们在这四个方法里面做的事情非常简单，就是在create时候发一个message，执行画面的绘制，在destory时remove这个消息。

从上面可以看出，动态壁纸实际上就是不断刷新的静态壁纸，越华丽越流畅，CPU就消耗越大，对于现在的本来电量就不怎么地的智能机来说，耗电也是很可观的。但是偶尔向朋友们炫一下还是绝对可行的。drawTime()与 drawCross()的内容可以由家自己实现，在TimeWall里，它们比较简单。drawTime()是计算下一处Time String应该移动到的坐标，以及画出这个String。drawCross()的作用是在用户触发onTouchEvent时画一个十字架。因为 TimeWall比较简单，如果大家自己实现的画图比较复杂，可以另外开启一个线程来刷新

UI

，否则有可能主线程被阻塞掉。

cube2.xml

<wallpaper xmlns:android=”http://schemas.android.com/apk/res/android”<br /> android:settingsActivity=”com.example.android.livecubes.cube2.CubeWallpaper2Settings”<br /> />

cube2_setting