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

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：

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

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

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"
        android:settingsActivity="com.example.android.livecubes.cube2.CubeWallpaper2Settings"
/>

cube2_setting

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
        android:title="@string/cube2_settings"
        android:key="cube2wallpaper_settings">
    <ListPreference
            android:key="cube2_shape"
            android:title="@string/cube2_settings_title"
            android:summary="@string/cube2_settings_summary"
            android:entries="@array/cube2_shapenames"
            android:entryValues="@array/cube2_shapeprefix" />
</PreferenceScreen>