What?

什么是壁纸？

android wallpaper包括锁屏壁纸和桌面壁纸，壁纸又区分静态和动态两种。我们每天使用手机第一眼看到的就是壁纸，好看的壁纸对于手机的颜值也有大大的提升（滑稽），就让我们对壁纸一探究竟吧。

本文基于Android 8.1源码，相关文件如下：

1./frameworks/base/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java

2./frameworks/base/services/core/java/android/app/WallpaperManager.java

3./frameworks/base/core/java/android/service/wallpaper/WallpaperService.java

4./frameworks/base/core/java/android/service/wallpaper/IwallpaperService.aidl

5./frameworks/base/packages/apps/SystemUI/src/com/android/systemui/statusbar/phone/LockscreenWallpaper.java

6./frameworks/base/packages/SystemUI/src/com/android/systemui/ImageWallpaper.java

7./frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java

How?

1.作为开发者如何去设置壁纸？

2.壁纸是怎么显示的？

3.壁纸存储在什么位置？

如何设置壁纸？举个栗子。

咱们手机中一般有内置主题的应用，在这里可以下载使用非常多好看的壁纸，点击即可设置为锁屏或桌面壁纸。

设置方法很简单，look:

WallpaperManager wallpaperManager = WallpaperManager.getInstance(this);
try {
wallpaperManager.setStream(InputStream,null,true,WallpaperManager.FLAG_LOCK);
} catch (IOException e) {e.printStackTrace();
}

三步骤：

1.添加设置壁纸的权限

<uses-permission android:name="android.permission.SET_WALLPAPER"/>

2.获取WallpaperManager对象

3.设置壁纸，四个参数分别对应：

a.InputStream:图片对于的输入流

b.visibleCropHint:图片裁剪相关，一般默认为null

c.allowBack:是否允许回退

d.which:壁纸分为锁屏壁纸和桌面壁纸，所以需要设置FLGA:锁屏壁纸--WallpaperManager.FLAG_LOCK,桌面壁纸：WallpaperManager.FLAG_SYSTEM

壁纸是如何显示的？

下面就对如上图中的每个过程做一个简单的分析：

1.setStream

try {//sGlobals.mService即WallpaperManagerServiceParcelFileDescriptor fd = sGlobals.mService.setWallpaper(null,mContext.getOpPackageName(), visibleCropHint, allowBackup,result, which, completion, UserHandle.myUserId());if (fd != null) {FileOutputStream fos = null;try {//将壁纸copy一份并存储到对应目录，默认是/data/system/users/0/wallpaper(或wallpaper_lock),其中0是主用户的userId，支持多用户fos = new ParcelFileDescriptor.AutoCloseOutputStream(fd);copyStreamToWallpaperFile(bitmapData, fos);fos.close();completion.waitForCompletion();} finally {IoUtils.closeQuietly(fos);}}} catch (RemoteException e) {throw e.rethrowFromSystemServer();}
}

2.WallpaperManagerService.java#setWallpaper

    @Overridepublic ParcelFileDescriptor setWallpaper(String name, String callingPackage,Rect cropHint, boolean allowBackup, Bundle extras, int which,IWallpaperManagerCallback completion, int userId) {//检查有没有设置壁纸的权限checkPermission(android.Manifest.permission.SET_WALLPAPER);//调用setStream方法的时候参数which必须是正确的if ((which & (FLAG_LOCK|FLAG_SYSTEM)) == 0) {final String msg = "Must specify a valid wallpaper category to set";Slog.e(TAG, msg);throw new IllegalArgumentException(msg);}/* If we're setting system but not lock, and lock is currently sharing the system* wallpaper, we need to migrate that image over to being lock-only before* the caller here writes new bitmap data.*///如果当前没有锁屏壁纸的话，并且是设置桌面壁纸即which == FLAG_SYSTEM，那么同时设置为锁屏壁纸if (which == FLAG_SYSTEM && mLockWallpaperMap.get(userId) == null) {if (DEBUG) {Slog.i(TAG, "Migrating system->lock to preserve");}migrateSystemToLockWallpaperLocked(userId);}ParcelFileDescriptor pfd = updateWallpaperBitmapLocked(name, wallpaper, extras);}

3.最主要的方法：WallpaperObserver#onEvent

WallpaperObserver是WallpaperManagerservice.java的内部类，它的主要职责是监听文件变化，也就是壁纸对应的文件更新,看下源码中关于它的注释：

/*** Observes the wallpaper for changes and notifies all IWallpaperServiceCallbacks* that the wallpaper has changed. The CREATE is triggered when there is no* wallpaper set and is created for the first time. The CLOSE_WRITE is triggered* every time the wallpaper is changed.*/

监听wallpaper变化并通知IWallpaperServiceCallbacks,前文提到的LockscreenWallpaper就是继承了

IWallpaperServiceCallbacks，并重写了它的onWallppaerChanged方法，在这里更新锁屏壁纸的。

 @Overridepublic void onEvent(int event, String path) {//如果是锁屏壁纸更新if (moved && lockWallpaperChanged) {notifyLockWallpaperChanged();//android 8.0新增的一个变化，锁屏包括下拉快捷的主题会根据当前的壁纸来变化，避免壁纸和锁屏的图标颜色一致导致的显示不清问题，但是有一个缺陷就是：//获取的是当前壁纸的主色调，而不是某个区域的主色调，这样就会导致虽然主色调是白色，比如时间的区域是黑色，这一点小米做的比较好，它是根据当前区域的壁纸的主色调来进行反色的。notifyWallpaperColorsChanged(wallpaper, FLAG_LOCK);return;}if (sysWallpaperChanged || lockWallpaperChanged) {notifyCallbacksLocked(wallpaper);}if (sysWallpaperChanged) {//桌面壁纸变化，那么bind ImageWallpaper，ImageWallpaper是负责显示静态桌面壁纸的// If this was the system wallpaper, rebind...bindWallpaperComponentLocked(mImageWallpaper, true,false, wallpaper, null);notifyColorsWhich |= FLAG_SYSTEM;}if (lockWallpaperChanged|| (wallpaper.whichPending & FLAG_LOCK) != 0) {if (DEBUG) {Slog.i(TAG, "Lock-relevant wallpaper changed");}// either a lock-only wallpaper commit or a system+lock event.// if it's system-plus-lock we need to wipe the lock bookkeeping;// we're falling back to displaying the system wallpaper there.//如果参数which是system+lock，也就是同时设置锁屏和桌面壁纸，那么remove锁屏壁纸，因为已经是同一张壁纸了if (!lockWallpaperChanged) {mLockWallpaperMap.remove(wallpaper.userId);}// and in any case, tell keyguard about itnotifyLockWallpaperChanged();notifyColorsWhich |= FLAG_LOCK;}}

先看锁屏壁纸更新这一部分：

void notifyLockWallpaperChanged() {final IWallpaperManagerCallback cb = mKeyguardListener;if (cb != null) {try {cb.onWallpaperChanged();} catch (RemoteException e) {// Oh well it went away; no big deal}}}

mKeyguardListener赋值的地方：

    @Overridepublic boolean setLockWallpaperCallback(IWallpaperManagerCallback cb) {checkPermission(android.Manifest.permission.INTERNAL_SYSTEM_WINDOW);synchronized (mLock) {mKeyguardListener = cb;}return true;}

前面我们说过LockscreenWallpaper.java是继承了IWallpaperManagerCallback的，那么setLockWallpaperCallback调用的地方应该是在这里：

  public LockscreenWallpaper(Context ctx, PhoneStatusBar bar, Handler h) {mService = IWallpaperManager.Stub.asInterface(ServiceManager.getService(Context.WALLPAPER_SERVICE));mWallpaperManager = (WallpaperManager) ctx.getSystemService(Context.WALLPAPER_SERVICE);try {//在这里给mKeyguardListener赋值的mService.setLockWallpaperCallback(this);} catch (RemoteException e) {Log.e(TAG, "System dead?" + e);}}

4.LockscreenWallpaper.java#onWallpaperChanged：

@Overridepublic void onWallpaperChanged() {// Called on Binder thread.mH.removeCallbacks(this);mH.post(this);}

LockscreenWallpaper实现了Runnable接口的，所以看下它的run方法：

    @Overridepublic void run() {// Called in response to onWallpaperChanged on the main thread.mLoader = new AsyncTask<Void, Void, LoaderResult>() {@Overrideprotected LoaderResult doInBackground(Void... params) {return loadBitmap(currentUser, selectedUser);}@Overrideprotected void onPostExecute(LoaderResult result) {super.onPostExecute(result);if (isCancelled()) {return;}if (result.success) {mCached = true;mCache = result.bitmap;mUpdateMonitor.setHasLockscreenWallpaper(result.bitmap != null);//通知StatsuBar更新壁纸mBar.updateMediaMetaData(true /* metaDataChanged */, true /* allowEnterAnimation */);}mLoader = null;}}.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);}

异步获取壁纸，并通知StatusBar去更新壁纸。

5.StatusBar.java#updateMediaMetaData:

这里主要就是对锁屏壁纸所在的View做最基本的setImageBitmap。

6.再看桌面壁纸部分：

6.1 bindWallpaperComponentLocked

if (sysWallpaperChanged) {// If this was the system wallpaper, rebind...bindWallpaperComponentLocked(mImageWallpaper, true,false, wallpaper, null);notifyColorsWhich |= FLAG_SYSTEM;}

mImageWallpaper = ComponentName.unflattenFromString(
context.getResources().getString(R.string.image_wallpaper_component));

也就是一开始提到的：

/frameworks/base/packages/SystemUI/src/com/android/systemui/ImageWallpaper.java

 boolean bindWallpaperComponentLocked(ComponentName componentName, boolean force,boolean fromUser, WallpaperData wallpaper, IRemoteCallback reply) {Intent intent = new Intent(WallpaperService.SERVICE_INTERFACE);WallpaperConnection newConn = new WallpaperConnection(wi, wallpaper);//componentName就是ImageWallpaperintent.setComponent(componentName);intent.putExtra(Intent.EXTRA_CLIENT_LABEL,com.android.internal.R.string.wallpaper_binding_label);intent.putExtra(Intent.EXTRA_CLIENT_INTENT, PendingIntent.getActivityAsUser(mContext, 0,Intent.createChooser(new Intent(Intent.ACTION_SET_WALLPAPER),mContext.getText(com.android.internal.R.string.chooser_wallpaper)),0, null, new UserHandle(serviceUserId)));}

ImageWallpaper继承了Service，既然是bindService，那么主要看下conn,也就是WallpaperConnection。

它的onServiceConnected方法：

   @Overridepublic void onServiceConnected(ComponentName name, IBinder service) {synchronized (mLock) {if (mWallpaper.connection == this) {mService = IWallpaperService.Stub.asInterface(service);attachServiceLocked(this, mWallpaper);// XXX should probably do saveSettingsLocked() later// when we have an engine, but I'm not sure about// locking there and anyway we always need to be able to// recover if there is something wrong.saveSettingsLocked(mWallpaper.userId);FgThread.getHandler().removeCallbacks(mResetRunnable);}}}

6.2 继续看attachServcieLocked方法：

void attachServiceLocked(WallpaperConnection conn, WallpaperData wallpaper) {try {conn.mService.attach(conn, conn.mToken,TYPE_WALLPAPER, false,wallpaper.width, wallpaper.height, wallpaper.padding);} catch (RemoteException e) {Slog.w(TAG, "Failed attaching wallpaper; clearing", e);if (!wallpaper.wallpaperUpdating) {bindWallpaperComponentLocked(null, false, false, wallpaper, null);}}}

conn.mService.attach是调用了IWallpaperServiceWrapper 的attach方法，IWallpaperServiceWrapper 继承了

IWallpaperService.Stub。

       @Overridepublic void attach(IWallpaperConnection conn, IBinder windowToken,int windowType, boolean isPreview, int reqWidth, int reqHeight, Rect padding) {new IWallpaperEngineWrapper(mTarget, conn, windowToken,windowType, isPreview, reqWidth, reqHeight, padding);}

在看它的构造方法，发送了一个DO_ATTACH的消息：

Message msg = mCaller.obtainMessage(DO_ATTACH);
mCaller.sendMessage(msg);

                 case DO_ATTACH: {try {mConnection.attachEngine(this);} catch (RemoteException e) {Log.w(TAG, "Wallpaper host disappeared", e);return;}Engine engine = onCreateEngine();mEngine = engine;mActiveEngines.add(engine);engine.attach(this);return;}

onCreateEngine也是一个抽象的方法：

   /*** Must be implemented to return a new instance of the wallpaper's engine.* Note that multiple instances may be active at the same time, such as* when the wallpaper is currently set as the active wallpaper and the user* is in the wallpaper picker viewing a preview of it as well.*/public abstract Engine onCreateEngine();

实现的地方仍然是在ImageWallpaper.java里

   @Overridepublic Engine onCreateEngine() {mEngine = new DrawableEngine();return mEngine;}

DrawableEngine是自定义的继承Engine的内部类

最后调用engine.attach方法。

WallpaperService.java的attach方法：

void attach(IWallpaperEngineWrapper wrapper) {onCreate(mSurfaceHolder);mInitializing = false;mReportedVisible = false;updateSurface(false, false, false);}

6.3 onCreate(mSurfaceHolder)

它是一个抽象方法

       /*** Called once to initialize the engine.  After returning, the* engine's surface will be created by the framework.*/public void onCreate(SurfaceHolder surfaceHolder) {}

它是一个抽象方法，那么真正的实现是在它的子类，也就是ImageWallpaper.java里

       @Overridepublic void onCreate(SurfaceHolder surfaceHolder) {if (DEBUG) {Log.d(TAG, "onCreate");}super.onCreate(surfaceHolder);mDefaultDisplay = getSystemService(WindowManager.class).getDefaultDisplay();setOffsetNotificationsEnabled(false);updateSurfaceSize(surfaceHolder, getDefaultDisplayInfo(), false /* forDraw */);}

surfaceHolder是在父类里初始化的，surfaceHolder = new BaseSurfaceHolder();

6.4 updateSurfaceSize

在这里主要是继续调用loadWallpaper方法去解析壁纸并最终绘制到surfaceHolder上。

6.5 drawFrame

对壁纸进行一些裁剪操作，根据是否支持硬件加速来决定绘制的方法：

    //支持硬件加速if (mIsHwAccelerated) {if (!drawWallpaperWithOpenGL(sh, availw, availh, xPixels, yPixels)) {drawWallpaperWithCanvas(sh, availw, availh, xPixels, yPixels);}} else {drawWallpaperWithCanvas(sh, availw, availh, xPixels, yPixels);if (FIXED_SIZED_SURFACE) {// If the surface is fixed-size, we should only need to// draw it once and then we'll let the window manager// position it appropriately.  As such, we no longer needed// the loaded bitmap.  Yay!// hw-accelerated renderer retains bitmap for faster rotationunloadWallpaper(false /* forgetSize */);}}

到这里，把壁纸的设置的简单过程基本上就讲完了，作为笔记做一个记录。

如有错误的地方，欢迎指正。

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