Aidl和Binder解析

先上实例代码：

service:

public class AidlService extends Service{

    @Override
    public IBinder onBind(Intent arg0) {
        /*return new AIDLTest.Stub() {

            @Override
            public String hello(String name) throws RemoteException {
                // TODO Auto-generated method stub
                return "hello"+name;
            }
        };*/
        return mBinder;
    }

    //一个类，继承了Binder，那么它的对象就可以被远程的进程使用了(前提是远程进程获取了这个类的对象【对象的引用】
    private final AIDLTest.Stub mBinder = new AIDLTest.Stub() {

        @Override
        public String hello(String name) throws RemoteException {
            // TODO Auto-generated method stub
            return "hello"+name;
        }
    };

client:

Intent intent = new Intent();
intent.setPackage("包名");
context.bindService(intent, serviceConnection,Context.BIND_AUTO_CREATE);

private ServiceConnection serviceConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        Log.d(TAG, "++++++ onServiceConnected: success ++++++");
        AIDLTest vasInterface = AIDLTest.Stub.asInterface(service);
    }

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

vasInterface.hello("aaaaaaaa");

解析：

最主要的部分是AS自动生成的AIDLTest文件：

/*
 * This file is auto-generated.  DO NOT MODIFY.
 * Original file: F:\Project\Practice\FrameworkDemo\app\src\main\aidl\com\example\admin\frameworkdemo\AIDLTest.aidl
 */
package com.example.admin.frameworkdemo;

public interface AIDLTest extends android.os.IInterface {
    /**
     * Local-side IPC implementation stub class.
     */
    public static abstract class Stub extends android.os.Binder implements com.example.admin.frameworkdemo.AIDLTest {
        private static final java.lang.String DESCRIPTOR = "com.example.admin.frameworkdemo.AIDLTest";

        /**
         * Construct the stub at attach it to the interface.
         */
        public Stub() {
            this.attachInterface(this, DESCRIPTOR);
        }

        /**
         * Cast an IBinder object into an com.example.admin.frameworkdemo.AIDLTest interface,
         * generating a proxy if needed.
         */
        public static com.example.admin.frameworkdemo.AIDLTest asInterface(android.os.IBinder obj) {
            if ((obj == null)) {
                return null;
            }
            android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
            if (((iin != null) && (iin instanceof com.example.admin.frameworkdemo.AIDLTest))) {
                return ((com.example.admin.frameworkdemo.AIDLTest) iin);
            }
            return new com.example.admin.frameworkdemo.AIDLTest.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_hello: {
                    data.enforceInterface(DESCRIPTOR);
                    java.lang.String _arg0;
                    _arg0 = data.readString();
                    java.lang.String _result = this.hello(_arg0);
                    reply.writeNoException();
                    reply.writeString(_result);
                    return true;
                }
            }
            return super.onTransact(code, data, reply, flags);
        }

        private static class Proxy implements com.example.admin.frameworkdemo.AIDLTest {
            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 java.lang.String hello(java.lang.String name) throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                java.lang.String _result;
                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    _data.writeString(name);
                    mRemote.transact(Stub.TRANSACTION_hello, _data, _reply, 0);
                    _reply.readException();
                    _result = _reply.readString();
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }
                return _result;
            }
        }

        static final int TRANSACTION_hello = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
    }

    public java.lang.String hello(java.lang.String name) throws android.os.RemoteException;
}

步骤：

如以下代码，在服务端，AidlService在被client端的bindservice启动之后，会执行onBind，返回一个继承于IBinder的类mBinder，

IBinder是底层的一个借口，实现该接口的类也具有了远程调用的能力，并重写了方法hello,这个后面再说。

private final AIDLTest.Stub mBinder = new AIDLTest.Stub() {

        @Override
        public String hello(String name) throws RemoteException {
            // TODO Auto-generated method stub
            return "hello"+name;
        }
    };

client端绑定成功之后，得到IBinder的继承类的应用，其实就是service端的mBinder的引用

private ServiceConnection serviceConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        Log.d(TAG, "++++++ onServiceConnected: success ++++++");
        vasInterface = AIDLTest.Stub.asInterface(service);
    }

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

client端紧接着执行

AIDLTest.Stub.asInterface(service);

进入asInterface：

public static com.example.admin.frameworkdemo.AIDLTest asInterface(android.os.IBinder obj) {
            if ((obj == null)) {
                return null;
            }
            android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
            if (((iin != null) && (iin instanceof com.example.admin.frameworkdemo.AIDLTest))) {
                return ((com.example.admin.frameworkdemo.AIDLTest) iin);
            }
            return new com.example.admin.frameworkdemo.AIDLTest.Stub.Proxy(obj);
        }

这里queryLocalInterface判断是跨进程调用，如果是跨进程调用，执行

return new com.example.admin.frameworkdemo.AIDLTest.Stub.Proxy(obj);

此时得到了一个Proxy类，传进去的obj是远程服务端的mBinder引用，即Proxy类持有远程服务端mBinder的引用。

此时回到client调用接口：

vasInterface.hello("aaaaaaaa");

此时我们知道vasInterface是一个AIDLTest.Stub.Proxy，执行里面的方法hello，

@Override
            public java.lang.String hello(java.lang.String name) throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                java.lang.String _result;
                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    _data.writeString(name);
                    mRemote.transact(Stub.TRANSACTION_hello, _data, _reply, 0);
                    _reply.readException();
                    _result = _reply.readString();
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }
                return _result;
            }

可以看到hello里面执行了可以看到里面执行了mRemote.transact(Stub.TRANSACTION_hello, _data, _reply, 0);

data代表了客户端传进去的数据，reply代表了服务端将要返回来的数据。

mRemote.transact(Stub.TRANSACTION_hello, _data, _reply, 0);

该方法实际上是通过底层的Binder驱动调用到C/C++层的JavaBBinder对象的tansact方法，而该方法通过JNI来调用JAVA 层上Binder对象的execTransact()方法，

并进而调用开发者自己可以覆盖的onTransact()方法从而达到了通信的目标

@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_hello: {
                    data.enforceInterface(DESCRIPTOR);
                    java.lang.String _arg0;
                    _arg0 = data.readString();
                    java.lang.String _result = this.hello(_arg0);
                    reply.writeNoException();
                    reply.writeString(_result);
                    return true;
                }
            }
            return super.onTransact(code, data, reply, flags);        }

这里面执行了：this.hello(_arg0)，而这个函数执行的应该就是子类mBinder在应用层定义的匿名类的里面的方法：

rivate final AIDLTest.Stub mBinder = new AIDLTest.Stub() {

        @Override
        public String hello(String name) throws RemoteException {
            // TODO Auto-generated method stub
            return "hello"+name;
        }
    };

然后通过reply.writeString(_result);将执行结果写到replay里面。

为什么AS自动生成的AIDLTest文件里面，Stub要定义为AIDLTest的内部类：

自动生成的aidl文件可能不止一个，Stub定义成内部类，使用的时候容易区分，比如：AIDLTest.Stub，AIDLTest2.Stub...