Android后台监听全局屏幕旋转

最近有个需求就是程序在后台监听手机的屏幕的旋转方向，废话不多说，先看看效果：

摸摸头~，既然是监听屏幕的旋转方向，那就需要要弄明白Android的屏幕是由谁控制的？，方向又是怎么控制的？

带着问题我们来一探究竟：

手机的屏幕管理类是WindowManager，那是不是可先去WindowManager类看看，从这个类里边并没法看到跟屏幕方向有关系方法~，在看该类的时候又发现了另一个类：

public class IWindowManagerImpl implements IWindowManager {...
}

通过对源码的一番撕扯，终于找到了一点蛛丝马迹：

public int watchRotation(IRotationWatcher arg0, int arg1) throws RemoteException

通过Android Studio看上边这个类会发现它实现的是IWindowManager，报红了，这个文件经过查询Android源代码发现是一个aidl文件，看看这个文件，最终发现屏幕的旋转方向监听是在IWindowManager.aidl文件中处理的，所以我们先看看这个文件：（sdk版本：7.1.1_r28）

package android.view;/**
* System private interface to the window manager.
*
* {@hide}
*/
interface IWindowManager
{....sdk<=25/*** Retrieve the current screen orientation, constants as per* {@link android.view.Surface}.*/int getRotation();sdk<=25/*** Watch the rotation of the screen.  Returns the current rotation,* calls back when it changes.*/int watchRotation(IRotationWatcher watcher);sdk>25/*** Watch the rotation of the specified screen.  Returns the current rotation,* calls back when it changes.*/int watchRotation(IRotationWatcher watcher, int displayId);/*** Remove a rotation watcher set using watchRotation.* @hide*/void removeRotationWatcher(IRotationWatcher watcher);/*** Lock the device orientation to the specified rotation, or to the* current rotation if -1.  Sensor input will be ignored until* thawRotation() is called.* @hide*/void freezeRotation(int rotation);....
}

这里主要看几个跟屏幕方向有关的方法，由于不同的sdk版本里边的函数也有所不同。所以我的想法就是通过这个IWindowManager接口来实现屏幕方向的监听，那么首先我们就需要获取到IWindowManager的实例。

再看看IWindowManager.aidl的实现类的部分代码，这里我们只需要关注如何获取IWindowManager的实例：


```java
public interface IWindowManager extends IInterface {void getBaseDisplaySize(int paramInt, Point paramPoint) throws RemoteException;void getInitialDisplaySize(int paramInt, Point paramPoint) throws RemoteException;void getRealDisplaySize(Point paramPoint) throws RemoteException;int getRotation() throws RemoteException;void removeRotationWatcher(IRotationWatcher paramIRotationWatcher) throws RemoteException;public static abstract class Stub extends Binder implements IWindowManager {private static final String DESCRIPTOR = "android.view.IWindowManager";static final int TRANSACTION_getBaseDisplaySize = 3;static final int TRANSACTION_getInitialDisplaySize = 1;static final int TRANSACTION_getRealDisplaySize = 2;static final int TRANSACTION_getRotation = 4;static final int TRANSACTION_removeRotationWatcher = 5;public Stub() {attachInterface(this, "android.view.IWindowManager");}public static IWindowManager asInterface(IBinder param1IBinder) {if (param1IBinder == null)return null;IInterface iInterface = param1IBinder.queryLocalInterface("android.view.IWindowManager");return (iInterface != null && iInterface instanceof IWindowManager) ? (IWindowManager) iInterface : new Proxy(param1IBinder);}public IBinder asBinder() {return (IBinder) this;}public boolean onTransact(int param1Int1, Parcel param1Parcel1, Parcel param1Parcel2, int param1Int2) throws RemoteException {Point point = new Point();if (param1Int1 != 1) {if (param1Int1 != 2) {if (param1Int1 != 3) {if (param1Int1 != 4) {if (param1Int1 != 5) {if (param1Int1 != 1598968902)return super.onTransact(param1Int1, param1Parcel1, param1Parcel2, param1Int2);param1Parcel2.writeString("android.view.IWindowManager");return true;}param1Parcel1.enforceInterface("android.view.IWindowManager");removeRotationWatcher(IRotationWatcher.Stub.asInterface(param1Parcel1.readStrongBinder()));param1Parcel2.writeNoException();return true;}param1Parcel1.enforceInterface("android.view.IWindowManager");param1Int1 = getRotation();param1Parcel2.writeNoException();param1Parcel2.writeInt(param1Int1);return true;}param1Parcel1.enforceInterface("android.view.IWindowManager");param1Int1 = param1Parcel1.readInt();point = new Point();getBaseDisplaySize(param1Int1, point);param1Parcel2.writeNoException();param1Parcel2.writeInt(1);point.writeToParcel(param1Parcel2, 1);return true;}point.enforceInterface("android.view.IWindowManager");point = new Point();getRealDisplaySize(point);param1Parcel2.writeNoException();param1Parcel2.writeInt(1);point.writeToParcel(param1Parcel2, 1);return true;}point.enforceInterface("android.view.IWindowManager");param1Int1 = point.readInt();Point point = new Point();getInitialDisplaySize(param1Int1, point);param1Parcel2.writeNoException();param1Parcel2.writeInt(1);point.writeToParcel(param1Parcel2, 1);return true;}private static class Proxy implements IWindowManager {private IBinder mRemote;Proxy(IBinder param2IBinder) {this.mRemote = param2IBinder;}public IBinder asBinder() {return this.mRemote;}public void getBaseDisplaySize(int param2Int, Point param2Point) throws RemoteException {Parcel parcel1 = Parcel.obtain();Parcel parcel2 = Parcel.obtain();try {parcel1.writeInterfaceToken("android.view.IWindowManager");parcel1.writeInt(param2Int);this.mRemote.transact(3, parcel1, parcel2, 0);parcel2.readException();if (parcel2.readInt() != 0)param2Point.readFromParcel(parcel2);return;} finally {parcel2.recycle();parcel1.recycle();}}public void getInitialDisplaySize(int param2Int, Point param2Point) throws RemoteException {Parcel parcel1 = Parcel.obtain();Parcel parcel2 = Parcel.obtain();try {parcel1.writeInterfaceToken("android.view.IWindowManager");parcel1.writeInt(param2Int);this.mRemote.transact(1, parcel1, parcel2, 0);parcel2.readException();if (parcel2.readInt() != 0)param2Point.readFromParcel(parcel2);return;} finally {parcel2.recycle();parcel1.recycle();}}public String getInterfaceDescriptor() {return "android.view.IWindowManager";}public void getRealDisplaySize(Point param2Point) throws RemoteException {Parcel parcel1 = Parcel.obtain();Parcel parcel2 = Parcel.obtain();try {parcel1.writeInterfaceToken("android.view.IWindowManager");this.mRemote.transact(2, parcel1, parcel2, 0);parcel2.readException();if (parcel2.readInt() != 0)param2Point.readFromParcel(parcel2);return;} finally {parcel2.recycle();parcel1.recycle();}}public int getRotation() throws RemoteException {Parcel parcel1 = Parcel.obtain();Parcel parcel2 = Parcel.obtain();try {parcel1.writeInterfaceToken("android.view.IWindowManager");this.mRemote.transact(4, parcel1, parcel2, 0);parcel2.readException();return parcel2.readInt();} finally {parcel2.recycle();parcel1.recycle();}}public void removeRotationWatcher(IRotationWatcher param2IRotationWatcher) throws RemoteException {Parcel parcel1 = Parcel.obtain();Parcel parcel2 = Parcel.obtain();try {parcel1.writeInterfaceToken("android.view.IWindowManager");if (param2IRotationWatcher != null) {IBinder iBinder = param2IRotationWatcher.asBinder();} else {param2IRotationWatcher = null;}parcel1.writeStrongBinder((IBinder) param2IRotationWatcher);this.mRemote.transact(5, parcel1, parcel2, 0);parcel2.readException();return;} finally {parcel2.recycle();parcel1.recycle();}}}}
}

代码可以看到，我们可以通过IWindowManager中的Stub的asInterface()方法返回IWindowManager的代理类Proxy，然后通过Proxy来调用相应的方法：

//加载得到ServiceManager类，然后得到方法getService。
Method getServiceMethod = Class.forName("android.os.ServiceManager").getDeclaredMethod("getService", new Class[]{String.class});
//通过getServiceMethod得到ServiceManager的实例（隐藏类，所以使用Object）
Object ServiceManager = getServiceMethod.invoke(null, new Object[]{"window"});
//通过反射的到Stub
Class<?> cStub = Class.forName("android.view.IWindowManager$Stub");
//得到Stub类的asInterface 方法
Method asInterface = cStub.getMethod("asInterface", IBinder.class);
//然后通过类似serviceManager.getIWindowManager的方法获取IWindowManager的实例
Object IWindowManager=asInterface.invoke(null, ServiceManager);

这里就拿到了IWindowManager的代理类，然后我们通过反射获取到watchRotation()函数：

Method watchRotation = IWindowManager.getClass().getDeclaredMethod("watchRotation",参数类型)

这里获取watchRotation函数需要知道它的参数类型以及参数的个数：

public static Class<?>[] getMethodParamTypes(Class<?> clazz, String methodName) {Method[] methods = clazz.getDeclaredMethods();for (Method method : methods) {Log.e("Service", "method = " + method.toGenericString());if (methodName.equals(method.getName())) {return method.getParameterTypes();}}return null;
}

修改watchRotation函数的获取方法：

Class<?> paramTypes = getMethodParamTypes(IWindowManager.getClass(),"watchRotation")
Method watchRotation = IWindowManager.getClass().getDeclaredMethod("watchRotation",paramTypes)

这里可以打印参数类型看看：

sdk>25
public int android.view.IWindowManager$Stub$Proxy.watchRotation(android.view.IRotationWatcher,int) throws android.os.RemoteExceptionsdk<=25
public int android.view.IWindowManager$Stub$Proxy.watchRotation(android.view.IRotationWatcher) throws android.os.RemoteException

需要一个IRotationWatcher和int类型的参数，IRotationWatcher接口后边讲。这里需要注意我们最开始说的版本兼容问题，因为我这里是在android 9手机上测试的，所以这里的watchRotation方法多了个int类型的参数，因此我们执行watchRotation方法的时候需要做版本适配：

public static int watchRotation(IRotationWatcher watcher) {int rotation = -1;try {Object iWindowManager = getIWindowManager();Class<?>[] paramTypes = ClassUtils.getMethodParamTypes(iWindowManager.getClass(), "watchRotation");Method watchRotation = ClassUtils.getMethod("watchRotation", iWindowManager.getClass(), paramTypes);if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {//这里做个适配rotation = (int) watchRotation.invoke(iWindowManager, watcher, 0);} else {rotation = (int) watchRotation.invoke(iWindowManager, watcher);}Log.e("Service", "rotation = " + rotation);} catch (Exception e) {e.printStackTrace();}return rotation;
}

接下来看看IRotationWatcher这个接口，查询资料发现也是一个Binder对象。思考一下，手机屏幕的旋转显然是在系统进程中监听的，所以这里就需要跨进程通讯获取到屏幕方向，先看看这个文件：

//RotationWatcher.aidlpackage android.view;/**
* {@hide}
*/
interface IRotationWatcher {void onRotationChanged(int rotation);
}

这里的IRotationWatcher是一个aidl接口，我们通过这个接口实现屏幕方向旋转结果的回调监听，所以这里我们只需要将这个文件拷贝到我们项目的aidl包中，包名必须是android.view才行：

编译后生成IRotationWatcher.java文件，然后我们创建一个Service，在Service中监听屏幕的旋转：

public class AccessService extends Service {public AccessService() {}@Overridepublic int onStartCommand(Intent intent, int flags, int startId) {Log.e("Service", "onStartCommand rotation = " + WindowUtils.watchRotation(new RotationWatcher()));return super.onStartCommand(intent, flags, startId);}@Overridepublic IBinder onBind(Intent intent) {throw new UnsupportedOperationException("Not yet implemented");}public static class RotationWatcher extends IRotationWatcher.Stub {@Overridepublic void onRotationChanged(int rotation) throws RemoteException {Log.e("Service", "onRotationChanged = " + rotation);}@Overridepublic IBinder asBinder() {return new RotationWatcher();}}
}

这里我们实现IRotationWatcher的回调方法onRotationChanged，然后创建IRotationWatcher的实例并传给watchRotation方法：

WindowUtils.watchRotation(new RotationWatcher())

ok，到此我们可以运行程序并切到后台后，然后切换手机的横竖屏，结果：

E/Service: onStartCommand rotation = 0E/Service: onRotationChanged = 1
E/Service: onRotationChanged = 0
E/Service: onRotationChanged = 3

可以看到，我们成功的监听到了屏幕方向的旋转！

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