文章记录自己的学习过程，供日后参考。

首先要知道壁纸设置的大体流程：上层应用调用wallpaperManager.setStream()或其他接口进行设置壁纸，WallpaperManagerService首先将壁纸copy到/data/system/user/0/目录下，WallpaperManagerService对该目录注册了一个WallpaperObserver，拷贝壁纸成功后会触发调用WallpaperObserver.onEvent()函数，onEvent()函数首先调用notifyCallbacksLocked()触发回调，然后再调用bindWallpaperComponentLocked()做进行进一步的壁纸更换。虽然整个壁纸机制有WallpaperManager、WallpaperService、ImageWallpaper、WallpaperManagerService、Globals、DrawableEngine、WallpaperData、WallpaperConnection等数据结构，感觉挺复杂的，我们应该剥离他的外表，看清他的本质。我们只要搞清了他们之间怎么交互的？交流些什么东西？就搞清楚了整个壁纸机制，说白了只要搞清楚IWallpaperService.aidl、IWallpaperEngine.aidl、IWallpaperConnection.aidl这三个文件就OK了，因为这三个文件是通信的关键所在。

1.IWallpaperService.aidl

oneway interface IWallpaperService {
    void attach(IWallpaperConnection connection,
    		IBinder windowToken, int windowType, boolean isPreview,
    		int reqWidth, int reqHeight);
}

(1).WallpaperService.IWallpaperServiceWrapper extends IWallpaperService.Stub；

(2).WallpaperService.onBind()

    /**
     * Implement to return the implementation of the internal accessibility
     * service interface.  Subclasses should not override.
     */
    @Override
    public final IBinder onBind(Intent intent) {
        return new IWallpaperServiceWrapper(this);
    }

WallPaperManagerService.bindWallpaperComponentLocked():

    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);
            intent.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)));
            if (!mContext.bindServiceAsUser(intent, newConn,
                    Context.BIND_AUTO_CREATE | Context.BIND_SHOWING_UI,
                    new UserHandle(serviceUserId))) {
           ..........
            }
   }

        public void onServiceConnected(ComponentName name, IBinder service) {
            synchronized (mLock) {
                if (mWallpaper.connection == this) {
                    mWallpaper.lastDiedTime = SystemClock.uptimeMillis();
                    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);
                }
            }
        }

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

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

            switch (message.what) {
                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;
                }

先上班，下班再研究。

析壁纸机制分析