调用后动态壁纸其实是显示在Activity的后面，而Activity则是透明显示，这样就可以看到下面的动态壁纸，如果Activity不是透明的则什么也看不到。

代码中有用到两个接口

IWallpaperService mService;

IWallpaperEngine mEngine;

我们可以看到该目录下面有三个aidl接口，分别是

复制代码 代码如下:
interface IWallpaperConnection {

    void attachEngine(IWallpaperEngine engine);

    ParcelFileDescriptor setWallpaper(String name);

}

oneway interface IWallpaperService {

    void attach(IWallpaperConnection connection,

            IBinder windowToken, int windowType, boolean isPreview,

            int reqWidth, int reqHeight);

}

oneway interface IWallpaperEngine {

    void setDesiredSize(int width, int height);

    void setVisibility(boolean visible);

    void dispatchPointer(in MotionEvent event);

    void dispatchWallpaperCommand(String action, int x, int y,            int z, in Bundle extras);

    void destroy();

}

定义壁纸管理和壁纸信息变量
复制代码 代码如下:
private WallpaperManager mWallpaperManager = null;

private WallpaperInfo mWallpaperInfo = null;

private WallpaperConnection mWallpaperConnection = null;

private Intent mWallpaperIntent;

初始化这些变量
复制代码 代码如下:
mWallpaperManager = WallpaperManager.getInstance(this);

mWallpaperInfo = mWallpaperManager.getWallpaperInfo();//如果返回null则说明当前不是动态壁纸

mWallpaperIntent = new Intent(WallpaperService.SERVICE_INTERFACE);

mWallpaperIntent.setClassName(mWallpaperInfo.getPackageName(), mWallpaperInfo.getServiceName());

绑定动态壁纸服务
复制代码 代码如下:
bindService(mIntent, this, Context.BIND_AUTO_CREATE);

IWallpaperService mService;//这里有一个adil接口

在连接监听中试着attach

复制代码 代码如下:
public void onServiceConnected(ComponentName name, IBinder service) {

                mService = IWallpaperService.Stub.asInterface(service);

                try {

                    mService.attach(this, view.getWindowToken(),

                    //        WindowManager.LayoutParams.TYPE_APPLICATION_MEDIA_OVERLAY,
                            WindowManager.LayoutParams.TYPE_APPLICATION_MEDIA,

                                  true, root.getWidth(), root.getHeight());

                } catch (RemoteException e) {

                    Log.w("", "Failed attaching wallpaper; clearing", e);
                }
        }

在bindService的时候发现总是失败，后来发现是权限问题，只有拥有系统权限的apk才可以使用WallpaperService.SERVICE_INTERFACE服务，所以问题就变成了怎么获取系统权限。