说明：Activity,Service,Application都是ContextWrapper的子类。ContextWrapper里面有一个Context类型的成员变量mBase，当然它实际的类型是ContextImpl。ContextWrapper实现方法的时候调用了mBase的方法。
继承关系图

image

注册广播和反注册必须是同一个Context，否则会出现Receiver not registered 异常。

ContextImpl:
@Override
public void unregisterReceiver(BroadcastReceiver receiver) {
if (mPackageInfo != null) {
IIntentReceiver rd = mPackageInfo.forgetReceiverDispatcher(
getOuterContext(), receiver);
try {
ActivityManagerNative.getDefault().unregisterReceiver(rd);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
} else {
throw new RuntimeException("Not supported in system context");
}
}

LoadApk:
根据context找到相应的Receiver
public IIntentReceiver forgetReceiverDispatcher(Context context,
BroadcastReceiver r) {
synchronized (mReceivers) {
ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher> map = mReceivers.get(context);
LoadedApk.ReceiverDispatcher rd = null;