ndroid AIDL與proxy,stub

1.簡單使用

利用android studio開發aidl還是非常方便的，建立一個aidl的後綴文件，在service與activity分別完成實現與引用就可以了
舉例：
aidl文件

interface IMyAidlInterface {
    void getInformation();
}

service

public class RemoteService extends Service {

    private IBinder mServiceBinder = new IMyAidlInterface.Stub(){
        @Override
        public void getInformation() {
            Log.i("RemoteService","information");
        }
    };

    public RemoteService() {
    }

    @Override
    public IBinder onBind(Intent intent) {
        return mServiceBinder;
    }
}

activity

public class MainActivity extends AppCompatActivity {

    IMyAidlInterface myAidlInterface;
    ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            myAidlInterface = IMyAidlInterface.Stub.asInterface(service);
            try {
                myAidlInterface.getInformation();
            } catch (RemoteException ex) {
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        startAndBindService();
    }

    private void startAndBindService() {
        Intent serviceIntent = new Intent(MainActivity.this, RemoteService.class);
        bindService(serviceIntent, connection, Context.BIND_AUTO_CREATE);
    }
}

輸出結果

I/RemoteService: information

2.理解proxy與stub的工作流程

aidl的後綴文件是Android studio的簡化處理，看一下IMyAidlInterface具體實現

public interface IMyAidlInterface extends android.os.IInterface
{
    public static abstract class Stub extends android.os.Binder implements com.example.testapplication.IMyAidlInterface
    {
        private static final java.lang.String DESCRIPTOR = "com.example.testapplication.IMyAidlInterface";
        public Stub()
        {
            this.attachInterface(this, DESCRIPTOR);
        }
        
        public static com.example.testapplication.IMyAidlInterface asInterface(android.os.IBinder obj)
        {
            if ((obj==null)) {
                return null;
            }
            android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
            if (((iin!=null)&&(iin instanceof com.example.testapplication.IMyAidlInterface))) {
                return ((com.example.testapplication.IMyAidlInterface)iin);
            }
            return new com.example.testapplication.IMyAidlInterface.Stub.Proxy(obj);
        }
        @Override public android.os.IBinder asBinder()
        {
            return this;
        }
        @Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException
        {
            switch (code)
            {
                case INTERFACE_TRANSACTION:
                {
                    reply.writeString(DESCRIPTOR);
                    return true;
                }
                case TRANSACTION_getInformation:
                {
                    data.enforceInterface(DESCRIPTOR);
                    this.getInformation();
                    reply.writeNoException();
                    return true;
                }
            }
            return super.onTransact(code, data, reply, flags);
        }
        private static class Proxy implements com.example.testapplication.IMyAidlInterface
        {
            private android.os.IBinder mRemote;
            Proxy(android.os.IBinder remote)
            {
                mRemote = remote;
            }
            @Override public android.os.IBinder asBinder()
            {
                return mRemote;
            }
            public java.lang.String getInterfaceDescriptor()
            {
                return DESCRIPTOR;
            }
            @Override public void getInformation() throws android.os.RemoteException
            {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    mRemote.transact(Stub.TRANSACTION_getInformation, _data, _reply, 0);
                    _reply.readException();
                }
                finally {
                    _reply.recycle();
                    _data.recycle();
                }
            }
        }
        static final int TRANSACTION_getInformation = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
    }
    public void getInformation() throws android.os.RemoteException;
}

我們聲明的接口IMyAidlInterface包含了一個靜態內部類Stub，並且Stub也繼承了IMyAidlInterface，所以Stub是IMyAidlInterface的具體實現，而Stub又是一個抽象類，最終的實現在RemoteService中
Stub內部包含了一個靜態內部類Proxy，同樣實現了接口IMyAidlInterface
可以通過前面的例子梳理一下Stub-proxy的工作流程

• RemoteService中的IBinder對象mServiceBinder是Stub的具體實現，在RemoteService和activity綁定的時候被返回
• 被返回的mServiceBinder最終是作爲onServiceConnected中的參數，
• Activity端會調用Stub中的靜態方法asInterface，mServiceBinder作爲參數，最後拿到IMyAidlInterface接口對象myAidlInterface

在asInterface方法中首先會判斷Binder是否處在當前進程，否則構造Proxy並返回，構造Proxy時，把mServiceBinder賦值給mRemote，Proxy中實現的接口getInformation會調用mRemote的transact方法，而Binder的通信是靠transact和onTransact實現的，最後會走到Stub的onTransact，完成對mServiceBinder的調用

所以，aidl通信體現着代理模式的設計思想，RemoteService具體實現了Stub，Proxy是Stub在本地Activity的代理對象，Proxy與Stub依靠transact和onTransact通信，Proxy與Stub的封裝設計最終很方便地完成了Activity與RemoteService跨進程通信