Android中使用AIDL接口实现进程间通信

AIDL接口可以实现进程间通信，现在这个项目中也使用到了，activity通过AIDL接口调用下层MainService的方法。现在自己又研究了一把，今天把用法和其中的原理记录下来。

使用AIDL接口

实现一个从activity传值给service的功能，activity和service要在不同进程。android studio新建project就有了MainActivity，然后创建一个AIDL文件，这是一个接口，要在其中申明方法：

IMyAidlInterface.aidl

// IMyAidlInterface.aidlpackage acxingyun.cetcs.com.binder;// Declare any non-default types here with import statementsinterface IMyAidlInterface {    /**     * Demonstrates some basic types that you can use as parameters     * and return values in AIDL.     */    void basicTypes(int a);}

参数a就是要传的值。下面build一下project，然后新建service，创建一个AIDL.stub类：
MyService1.java

public class MyService1 extends Service {    private IMyAidlInterface.Stub iMyAidlInterface = new IMyAidlInterface.Stub() {        @Override        public void basicTypes(int a) throws RemoteException {            Log.i("MyService1", "basicTypes called,a:" + a);        }    };    public MyService1() {    }    @Override    public IBinder onBind(Intent intent) {        // TODO: Return the communication channel to the service.        return iMyAidlInterface;    }    @Override    public void onCreate() {        Log.i(getClass().getSimpleName(), "onCreate...");        super.onCreate();    }}

在onBind中返回AIDL.stub给activity,activity通过bindservice得到AIDL.stub:

MainActivity.java

public class MainActivity extends AppCompatActivity {    private final String TAG = getClass().getSimpleName();    private Button bt1;    private Button bt2;    private IMyAidlInterface iMyAidlInterface;    private static final ComponentName SERVICE_COMPONENT = new ComponentName(            "acxingyun.cetcs.com.binder", "acxingyun.cetcs.com.binder.MyService1");    private ServiceConnection serviceConnection = new ServiceConnection() {        @Override        public void onServiceConnected(ComponentName name, IBinder service) {            Log.i("MainActivity", "onServiceConnected...");            iMyAidlInterface = IMyAidlInterface.Stub.asInterface(service);        }        @Override        public void onServiceDisconnected(ComponentName name) {        }    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        bt1 = (Button) findViewById(R.id.bt1);        bt2 = (Button) findViewById(R.id.bt2);        bt1.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                Log.i("MainActivity", "bt1 clicked...");                Intent intent = new Intent();                intent.setComponent(SERVICE_COMPONENT);                bindService(intent, serviceConnection, BIND_AUTO_CREATE);            }        });        bt2.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                Log.i("MainActivity", "bt2 clicked...");                if (iMyAidlInterface != null){                    try {                        iMyAidlInterface.basicTypes(100);                    } catch (RemoteException e) {                        e.printStackTrace();                    }                }            }        });    }}

由于service和activity要在不同进程，在manifest中配置service:

<service    android:name=".MyService1"    android:enabled="true"    android:exported="true"    android:process=":MyService" />

点击button1：

06-05 05:15:43.913 2630-2630/acxingyun.cetcs.com.binder I/MainActivity: bt1 clicked...06-05 05:15:43.942 1018-1508/system_process I/ActivityManager: Start proc 2654:acxingyun.cetcs.com.binder:MyService/u0a72 for service acxingyun.cetcs.com.binder/.MyService106-05 05:15:43.977 2654-2654/acxingyun.cetcs.com.binder:MyService I/MyService1: onCreate...06-05 05:15:43.978 2630-2630/acxingyun.cetcs.com.binder I/MainActivity: onServiceConnected...

MainActivity和service在不同进程，点击bt2调用aidl接口：

06-05 05:18:46.332 2630-2630/acxingyun.cetcs.com.binder I/MainActivity: bt2 clicked...06-05 05:18:46.333 2654-2670/acxingyun.cetcs.com.binder:MyService I/MyService1: basicTypes called,a:100

service得到了activity传的参数。

AIDL通信原理浅析

service端是一个AIDL.stub类：

    private IMyAidlInterface.Stub iMyAidlInterface = new IMyAidlInterface.Stub() {        @Override        public void basicTypes(int a) throws RemoteException {            Log.i("MyService1", "basicTypes called,a:" + a);        }    };

这个stub类通过onBind返回：

    @Override    public IBinder onBind(Intent intent) {        // TODO: Return the communication channel to the service.        return iMyAidlInterface;    }

发现stub实际上是一个IBinder对象，activity端得到之后做了转换：

    private IMyAidlInterface iMyAidlInterface;    private ServiceConnection serviceConnection = new ServiceConnection() {        @Override        public void onServiceConnected(ComponentName name, IBinder service) {            Log.i("MainActivity", "onServiceConnected...");            iMyAidlInterface = IMyAidlInterface.Stub.asInterface(service);        }        @Override        public void onServiceDisconnected(ComponentName name) {        }    };

通过IMyAidlInterface.Stub.asInterface(service)变成了之前定义的AIDL接口，于是通过这个AIDL接口就可以调用service端的方法：

iMyAidlInterface.basicTypes(100);

build工程后会自动生成一个IMyAidlInterface.java文件，里面包含了activity端和service端数据传递的代码，先贴出来慢慢说：

public interface IMyAidlInterface extends android.os.IInterface{/** Local-side IPC implementation stub class. */public static abstract class Stub extends android.os.Binder implements acxingyun.cetcs.com.binder.IMyAidlInterface{private static final java.lang.String DESCRIPTOR = "acxingyun.cetcs.com.binder.IMyAidlInterface";/** Construct the stub at attach it to the interface. */public Stub(){this.attachInterface(this, DESCRIPTOR);}/** * Cast an IBinder object into an acxingyun.cetcs.com.binder.IMyAidlInterface interface, * generating a proxy if needed. */public static acxingyun.cetcs.com.binder.IMyAidlInterface asInterface(android.os.IBinder obj){if ((obj==null)) {return null;}android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);if (((iin!=null)&&(iin instanceof acxingyun.cetcs.com.binder.IMyAidlInterface))) {return ((acxingyun.cetcs.com.binder.IMyAidlInterface)iin);}return new acxingyun.cetcs.com.binder.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_basicTypes:{data.enforceInterface(DESCRIPTOR);int _arg0;_arg0 = data.readInt();this.basicTypes(_arg0);reply.writeNoException();return true;}}return super.onTransact(code, data, reply, flags);}private static class Proxy implements acxingyun.cetcs.com.binder.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;}/**     * Demonstrates some basic types that you can use as parameters     * and return values in AIDL.     */@Override public void basicTypes(int a) throws android.os.RemoteException{android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();try {_data.writeInterfaceToken(DESCRIPTOR);_data.writeInt(a);mRemote.transact(Stub.TRANSACTION_basicTypes, _data, _reply, 0);_reply.readException();}finally {_reply.recycle();_data.recycle();}}}static final int TRANSACTION_basicTypes = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);}/**     * Demonstrates some basic types that you can use as parameters     * and return values in AIDL.     */public void basicTypes(int a) throws android.os.RemoteException;}

这排版看的蛋疼，大致梳理下，最外层是aidl接口，申明了一个方法basicTypes(int a)，stub是aidl的一个内部类，继承Binder实现了aidl接口，因此可以以IBinder形式返回给activity，它包含了三个方法：asInterface(),asBinder(),onTransact(),stub还有一个内部类Proxy。先从service创建开始，定义了一个stub对象：

private IMyAidlInterface.Stub iMyAidlInterface = new IMyAidlInterface.Stub() {        @Override        public void basicTypes(int a) throws RemoteException {            Log.i("MyService1", "basicTypes called,a:" + a);        }    };

 stub类要在service端实现aidl接口的方法。在onBind()中返回：

    @Override    public IBinder onBind(Intent intent) {        // TODO: Return the communication channel to the service.        return iMyAidlInterface;    }

activity中得到stub对象并转换成aidl对象：

    private IMyAidlInterface iMyAidlInterface;    private ServiceConnection serviceConnection = new ServiceConnection() {        @Override        public void onServiceConnected(ComponentName name, IBinder service) {            Log.i("MainActivity", "onServiceConnected...");            iMyAidlInterface = IMyAidlInterface.Stub.asInterface(service);        }        @Override        public void onServiceDisconnected(ComponentName name) {        }    };

 用到了IMyAidlInterface.Stub.asInterface(service)，回到源码中：

public static acxingyun.cetcs.com.binder.IMyAidlInterface asInterface(android.os.IBinder obj){if ((obj==null)) {return null;}android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);if (((iin!=null)&&(iin instanceof acxingyun.cetcs.com.binder.IMyAidlInterface))) {return ((acxingyun.cetcs.com.binder.IMyAidlInterface)iin);}return new acxingyun.cetcs.com.binder.IMyAidlInterface.Stub.Proxy(obj);}

iin是调用IBinder.queryLocalInterface()得到的：

    public IInterface queryLocalInterface(String descriptor) {        if (mDescriptor.equals(descriptor)) {            return mOwner;        }        return null;    }

queryLocalInterface结果又和 mDescriptor有关，mDescriptor是在stub的构造函数中赋值：

private static final java.lang.String DESCRIPTOR = "acxingyun.cetcs.com.binder.IMyAidlInterface";/** Construct the stub at attach it to the interface. */public Stub(){this.attachInterface(this, DESCRIPTOR);}

进去看：

    public void attachInterface(IInterface owner, String descriptor) {        mOwner = owner;        mDescriptor = descriptor;    }

传进去的descriptor和mDescriptor 都是一样的，关键是queryLocalInterface返回的对象mOwner，是stub类的this，也就是stub对象，不是一个IMyAidlInterface实例，所以最后会返回：

acxingyun.cetcs.com.binder.IMyAidlInterface.Stub.Proxy(obj);

Proxy(obj)是一个proxy类：

private static class Proxy implements acxingyun.cetcs.com.binder.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;}/**     * Demonstrates some basic types that you can use as parameters     * and return values in AIDL.     */@Override public void basicTypes(int a) throws android.os.RemoteException{android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();try {_data.writeInterfaceToken(DESCRIPTOR);_data.writeInt(a);mRemote.transact(Stub.TRANSACTION_basicTypes, _data, _reply, 0);_reply.readException();}finally {_reply.recycle();_data.recycle();}}}

activity调用aidl方法也就是在proxy类中调用aidl的方法basicTypes()，由于obj实际上是aidl.stub对象，也就是把service传来的stub对象给了mRemote，mRemote.transact(Stub.TRANSACTION_basicTypes, _data, _reply, 0)，就是stub.transact()方法，就是Binder.transact()，里面又会调用Binder.onTransact(),而Binder.onTransact()又在stub继承Binder的时候被override了：

@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_basicTypes:{data.enforceInterface(DESCRIPTOR);int _arg0;_arg0 = data.readInt();this.basicTypes(_arg0);reply.writeNoException();return true;}}return super.onTransact(code, data, reply, flags);}

于是，根据传的参数code，进入case TRANSACTION_basicTypes，调用this.basicTypes(_arg0)，也就是当前IMyAidlInterface.java申明的方法basicTypes（int a）,实现又是在service中，最后实现了activity对service方法的调用。