Java 服务代理对象的获取过程

// ./packages/experimental/Freg/src/shy/luo/freg/Freg.java
public class Freg extends Activity implements onClickListener {

    ......
    private IFregService fregService = null;
    ......

    @Override
    public void onCreate(Bundle savedInstanceState) {
        ......
        fregService = IFregService.Stub.asInterface(ServiceManager.getService("freg"));
        ......
    }
    ......
}

getService

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

sCache 用来保存已经获得的 JavaBinderProxy.

class ServiceManagerProxy implements IServiceManager {
    public ServiceManagerProxy(IBinder remote) {
        mRemote = remote;
    }
    
    public IBinder asBinder() {
        return mRemote;
    }
    
    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;
    }
}

class Parcel {
    ......
    /**
     * Read an object from the parcel at the current dataPosition().
     */
    public final IBinder readStrongBinder() {
        return nativeReadStrongBinder(mNativePtr);
    }
    ......
}

static jobject android_os_Parcel_readStrongBinder(JNIEnv* env, jclass clazz, jlong nativePtr)
{
    Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);
    if (parcel != NULL) {
        return javaObjectForIBinder(env, parcel->readStrongBinder());
    }
    return NULL;
}

• parcel->readStrongBinder 获得 BpBinder.
• javaObjectForIBinder 将 BpBinder 转换成 Java BinderProxy

asInterface

public interface IFregService extends android.os.IInterface {
    /** Local-side IPC implementation stub class. */
    public static abstract class Stub extends android.os.Binder implements
            android.os.IFregService {
        private static final java.lang.String DESCRIPTOR = "android.os.IFregService";
 
        /** Construct the stub at attach it to the interface. */
        public Stub() {
            this.attachInterface(this, DESCRIPTOR);
        }
 
        /**
         * Cast an IBinder object into an android.os.IFregService interface,
         * generating a proxy if needed.
         */
        public static android.os.IFregService asInterface(android.os.IBinder obj) {
            if ((obj == null)) {
                return null;
            }
            android.os.IInterface iin = (android.os.IInterface) obj
                    .queryLocalInterface(DESCRIPTOR);
            if (((iin != null) && (iin instanceof android.os.IFregService))) {
                return ((android.os.IFregService) iin);
            }
            return new android.os.IFregService.Stub.Proxy(obj);
        }
    }
}
 

asInterface 中 obj 参数是 Java BinderProxy, 所以 queryLocalInterface 返回 null.然后就会创建 android.os.IFregService.Stub.Proxy.