AIDL文件简析

本文简单介绍一下aidl文件build所生成的文件。
首先我们先新建一个aidl文件，like this：

// IMyAidlInterface.aidl
package com.learn.cxx.learn;

// Declare any non-default types here with import statements

interface IMyAidlInterface {
    /**
     * Demonstrates some basic types that you can use as parameters
     * and return values in AIDL.
     */
    void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat,
            double aDouble, String aString);
}

很简单，系统会默认帮我们生成一个作演示用的方法。然后我们rebuild一下工程，在build/generated/source/aidl/debug/com.learn.cxx.learn目录下面就会生成一个名为IMyAidlInterface.java的文件。如下：

/*
 * This file is auto-generated.  DO NOT MODIFY.
 * Original file: /home/cxx/dev/android/workspace/Learn/app/src/main/aidl/com/learn/cxx/learn/IMyAidlInterface.aidl
 */
package com.learn.cxx.learn;
// Declare any non-default types here with import statements

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

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

        /**
         * Cast an IBinder object into an com.learn.cxx.learn.IMyAidlInterface interface,
         * generating a proxy if needed.
         */
        public static com.learn.cxx.learn.IMyAidlInterface asInterface(android.os.IBinder obj) {
            if ((obj == null)) {
                return null;
            }
            android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
            if (((iin != null) && (iin instanceof com.learn.cxx.learn.IMyAidlInterface))) {
                return ((com.learn.cxx.learn.IMyAidlInterface) iin);
            }
            return new com.learn.cxx.learn.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();
                    long _arg1;
                    _arg1 = data.readLong();
                    boolean _arg2;
                    _arg2 = (0 != data.readInt());
                    float _arg3;
                    _arg3 = data.readFloat();
                    double _arg4;
                    _arg4 = data.readDouble();
                    java.lang.String _arg5;
                    _arg5 = data.readString();
                    this.basicTypes(_arg0, _arg1, _arg2, _arg3, _arg4, _arg5);
                    reply.writeNoException();
                    return true;
                }
            }
            return super.onTransact(code, data, reply, flags);
        }

        private static class Proxy implements com.learn.cxx.learn.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 anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) 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(anInt);
                    _data.writeLong(aLong);
                    _data.writeInt(((aBoolean) ? (1) : (0)));
                    _data.writeFloat(aFloat);
                    _data.writeDouble(aDouble);
                    _data.writeString(aString);
                    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 anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException;
}

代码很长，看着眼晕，上一张UML图：

UML画的不好，将就看一下。结构其实很清晰，继承关系我也不讲了。
我们在继承Service类实现自己的Service时，可重载onBind方法，并将一个ServiceClass实例作为返回值，onBind方法的返回类型是IBinder，显然，ServiceClass是可以作为返回值的。
在bindService时我们可以传入一个ServiceConnection对象，并获取到Service返回给我们的IBinder(也就是一个ServiceClass实例)，然后通过Stub中的一个共有静态方法asInterface就可以将该IBinder对象转换为我们可以使用的IMyAidlInterface对象。我们通过操作IMyAidlInterface对象完成与服务端的通信。
以上。

参考：
在Android studio里面使用AIDL