AMS之代理模式.png
- IActivityManager是ActivityManagerNative与ActivityManagerProxy共同的接口
- ActivityManagerPorxy含有一个IBinder对象mRemote，而抽象类ActivityManagerNative继承了IBinder的实现类Binder，这就决定了当Proxy发起调用后将由Native的实现类来接受调用
- 本地客户端：ActivityManager
- 远程服务端：ActivityManagerService
- 代理类：ActivityManagerNative的内部类ActivityManagerProxy，它接受客户端的“委托”向服务端发起调用
- 客户端与服务端通过Binder机制进行跨进程通信：以客户端调用getRecentTasks()为例
- ActivityManager发起本地调用
public List<RecentTaskInfo> getRecentTasks(int maxNum, int flags)
throws SecurityException {
try {
return ActivityManagerNative.getDefault().getRecentTasks(maxNum,
flags, UserHandle.myUserId());
} catch (RemoteException e) {
// System dead, we will be dead too soon!
return null;
}
}
- ActivityManagerNative获取ActivityManagerServicer的本地代理
static public IActivityManager getDefault() {
return gDefault.get();
}
private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
protected IActivityManager create() {
IBinder b = ServiceManager.getService("activity");
if (false) {
Log.v("ActivityManager", "default service binder = " + b);
}
IActivityManager am = asInterface(b);
if (false) {
Log.v("ActivityManager", "default service = " + am);
}
return am;
}
};
static public IActivityManager asInterface(IBinder obj) {
if (obj == null) {
return null;
}
IActivityManager in =
(IActivityManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ActivityManagerProxy(obj);
}
- 代理ActivityManagerProxy对象使用Binder的transact方法向远端发起调用
public List<ActivityManager.RecentTaskInfo> getRecentTasks(int maxNum,
int flags, int userId) throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeInt(maxNum);
data.writeInt(flags);
data.writeInt(userId);
mRemote.transact(GET_RECENT_TASKS_TRANSACTION, data, reply, 0);
reply.readException();
ArrayList<ActivityManager.RecentTaskInfo> list
= reply.createTypedArrayList(ActivityManager.RecentTaskInfo.CREATOR);
data.recycle();
reply.recycle();
return list;
}
- ActivityManagerNative使用onTransact()方法接受远程调用
case GET_RECENT_TASKS_TRANSACTION: {
data.enforceInterface(IActivityManager.descriptor);
int maxNum = data.readInt();
int fl = data.readInt();
int userId = data.readInt();
List<ActivityManager.RecentTaskInfo> list = getRecentTasks(maxNum,
fl, userId);
reply.writeNoException();
reply.writeTypedList(list);
return true;
}
- 由于ActivityManagerNative是一个抽象类，因此getRecentTasks()的具体实现在它的子类ActivityManagerService中
@Override
public List<ActivityManager.RecentTaskInfo> getRecentTasks(int maxNum, int flags, int userId) {
final int callingUid = Binder.getCallingUid();
userId = handleIncomingUser(Binder.getCallingPid(), callingUid, userId,
false, ALLOW_FULL_ONLY, "getRecentTasks", null);
final boolean includeProfiles = (flags & ActivityManager.RECENT_INCLUDE_PROFILES) != 0;
final boolean withExcluded = (flags&ActivityManager.RECENT_WITH_EXCLUDED) != 0;
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