多态的背后

1、Activity中：

private Window mWindow = null;

mWindow = getWindow();

Log.d(tag, "mWindow.getClass().getName() is: " + mWindow.getClass().getName());

D/MainActivity(  437): mWindow.getClass().getName() is: com.android.internal.policy.impl.PhoneWindow

2、Activity中：

private WindowManager mWindowManager = null;

mWindowManager = getWindowManager();

Log.d(tag, "mWindowManager.getClass().getName() is: " + mWindowManager.getClass().getName());

D/MainActivity(  437): mWindowManager.getClass().getName() is: android.view.Window$LocalWindowManager

3、ServiceManager(java)中：

private IServiceManager mISM = null;

mISM = ServiceManager.getIServiceManager();
Log.d(tag, "mISM.toString() is: " + mISM.toString());
Log.d(tag, "mISM.getClass().getName() is: " + mISM.getClass().getName());

D/ServiceManager002Activity(  712): mISM.toString() is: android.os.ServiceManagerProxy@40f169f0
D/ServiceManager002Activity(  712): mISM.getClass().getName() is: android.os.ServiceManagerProxy

4、Context.ACTIVITY_SERVICE

IBinder activity = ServiceManager.getService(Context.ACTIVITY_SERVICE);
Log.d(tag, "activity.toString() is: " + activity.toString());
Log.d(tag, "activity.getClass().getName() is: " + activity.getClass().getName());

D/ServiceManager002Activity(  712): activity.toString() is: android.os.BinderProxy@40f16a80
D/ServiceManager002Activity(  712): activity.getClass().getName() is: android.os.BinderProxy

5、Context.ALARM_SERVICE

IBinder alarm = ServiceManager.getService(Context.ALARM_SERVICE);
Log.d(tag, "alarm.toString() is: " + alarm.toString());
Log.d(tag, "alarm.getClass().getName() is: " + alarm.getClass().getName());

D/ServiceManager002Activity(  712): alarm.toString() is: android.os.BinderProxy@40f18228
D/ServiceManager002Activity(  712): alarm.getClass().getName() is: android.os.BinderProxy

6、Context.INPUT_METHOD_SERVICE

IBinder input_method  = ServiceManager.getService(Context.INPUT_METHOD_SERVICE);
Log.d(tag, "input_method.toString() is: " + input_method.toString());
Log.d(tag, "input_method.getClass().getName() is: " + input_method.getClass().getName());

D/ServiceManager002Activity(  712): input_method.toString() is: android.os.BinderProxy@40f4a7b0

D/ServiceManager002Activity(  712): input_method.getClass().getName() is: android.os.BinderProxy

7、Context.POWER_SERVICE

IBinder power  = ServiceManager.getService(Context.POWER_SERVICE);
Log.d(tag, "power.toString() is: " + power.toString());
Log.d(tag, "power.getClass().getName() is: " + power.getClass().getName());

D/ServiceManager002Activity(  712): power.toString() is: android.os.BinderProxy@40f34c38
D/ServiceManager002Activity(  712): power.getClass().getName() is: android.os.BinderProxy

8、Context.WINDOW_SERVICE

IBinder window  = ServiceManager.getService(Context.WINDOW_SERVICE);
Log.d(tag, "window.toString() is: " + window.toString());
Log.d(tag, "window.getClass().getName() is: " + window.getClass().getName());

D/ServiceManager002Activity(  712): window.toString() is: android.os.BinderProxy@40f180a0

D/ServiceManager002Activity(  712): window.getClass().getName() is: android.os.BinderProxy

ServiceManager.getService()函数的源码为如下：

public static IBinder getService(String name) 
{
        try 
{
            IBinder service = sCache.get(name);
            if (service != null)
{
                return service;
            }
else
{
                return getIServiceManager().getService(name);
            }
        } 
catch (RemoteException e)
{
            Log.e(TAG, "error in getService", e);
        }

        return null;
}

该函数中又调用：getIServiceManager().getService(name);

    private static IServiceManager getIServiceManager() 
{
        if (sServiceManager != null)
{
            return sServiceManager;
        }


        // Find the service manager
        sServiceManager = ServiceManagerNative.asInterface(BinderInternal.getContextObject());

        return sServiceManager;
    }

通过Point 3可以知道getIServiceManager的返回值是 android.os.ServiceManagerProxy类型的，

调用 android.os.ServiceManagerProxy的getService函数：

    public IBinder getService(String name) throws RemoteException {
        Parcel data = Parcel.obtain();
        Parcel reply = Parcel.obtain();
        data.writeInterfaceToken(IServiceManager.descriptor);
        data.writeString(name);
        mRemote.transact(GET_SERVICE_TRANSACTION, data, reply, 0);
        IBinder binder = reply.readStrongBinder();
        reply.recycle();
        data.recycle();
        return binder;
    }

该代理会与ServiceManager的Server部分进行通信。

9、BinderInternal.getContextObject()

private IBinder mIBinder = null;

mIBinder = BinderInternal.getContextObject();
Log.d(tag, "mIBinder.toString() is: " + mIBinder.toString());
Log.d(tag, "mIBinder.getClass().getName() is: " + mIBinder.getClass().getName());

D/ActivityManagerNative002Activity(  743): mIBinder.toString() is: android.os.BinderProxy@40f17310

D/ActivityManagerNative002Activity(  743): mIBinder.getClass().getName() is: android.os.BinderProxy

10、ServiceManagerProxy的成员变量：mRemote

Log.d(tag, "remote.toString() is: " + remote.toString());
Log.d(tag, "remote.getClass().getName() is: " + remote.getClass().getName());

D/ServiceManager002Activity(  730): remote.toString() is: android.os.BinderProxy@40f14c80
D/ServiceManager002Activity(  730): remote.getClass().getName() is: android.os.BinderProxy

mRemote的值与ServiceManager中调用BinderInternal.getContextObject()的返回值是一致的：

ServiceManager中：ServiceManagerNative.asInterface(BinderInternal.getContextObject())

ServiceManagerNative中：new ServiceManagerProxy(obj)  obj是BinderInternal.getContextObject()的返回值

ServiceManagerProxy中：mRemote = remote remote是ServiceManagerProxy构造函数的参数

因此，mRemote实际就是BinderInternal.getContextObject()的返回值