AIDL的简单使用以及Binder机制源码解析

本篇是在https://www.jianshu.com/p/4ee3fd07da14基础上写的。方便自己日后回忆。
一、aidl的简单使用
aidl的使用很简单，其实就是创建一个aidl文件，

interface IRemoteInterface {
void test();
int add(int a,int b);
    /**
     * 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);
}

会自动生成一个继承Binder的实现aidl接口的Stub类，这个然后在service（进程1）中onBind方法中返回这个binder（如下代码）

public class RemoteService extends Service {
    // 实例化AIDL的Stub类(Binder的子类)
    IRemoteInterface.Stub mBinder = new IRemoteInterface.Stub(){

        @Override
        public void test() throws RemoteException {
            System.out.println("客户端通过AIDL与远程后台成功通信");
        }

        @Override
        public int add(int a, int b) throws RemoteException {
            return a+b;
        }

        @Override
        public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, String aString) throws RemoteException {
        }
    };

    //重写与Service生命周期的相关方法
    @Override
    public void onCreate() {
        super.onCreate();

        System.out.println("执行了onCreat()");

    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        System.out.println("执行了onStartCommand()");
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        System.out.println("执行了onDestory()");
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {

        System.out.println("执行了onBind()");
        //在onBind()返回继承自Binder的Stub类型的Binder，非常重要
        return mBinder;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        System.out.println("执行了onUnbind()");
        return super.onUnbind(intent);
    }


}

然后在client（进程2）中拿到server传过来的binder（代理），即可通过这个server中的binder代理来调用aidl中写好的方法。从而实现IPC。

public class MainActivity extends AppCompatActivity {
 Button btn,btn2;
 private IRemoteInterface iRemoteInterface;
    //创建ServiceConnection的匿名类
    private ServiceConnection connection=new ServiceConnection() {
        //重写onServiceConnected()方法和onServiceDisconnected()方法
        //在Activity与Service建立关联和解除关联的时候调用

        //在Activity与Service建立关联时调用
        @Override
     public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            //IRemoteInterface.Stub.asInterface()方法获取服务器端返回的IBinder对象
            //将IBinder对象传换成了IRemoteInterface接口对象
            iRemoteInterface=IRemoteInterface.Stub.asInterface(iBinder);
            try {
                iRemoteInterface.test();
                int result=iRemoteInterface.add(1,2);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

     @Override
     public void onServiceDisconnected(ComponentName componentName) {

     }
 };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn=findViewById(R.id.btn);
        btn2=findViewById(R.id.btn2);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//通过Intent指定服务端的服务名称和所在包，与远程Service进行绑定
                //参数与服务器端的action要一致,即"服务器包名.aidl接口文件名"
                Intent intent = new Intent("com.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface");

                //Android5.0后无法只通过隐式Intent绑定远程Service
                //需要通过setPackage()方法指定包名
                intent.setPackage("com.example.zhaoziliang.rxjavaandretrofitdemo");

                //绑定服务,传入intent和ServiceConnection对象
                bindService(intent, connection, Context.BIND_AUTO_CREATE);

            }
        });
        btn2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try {
                    iRemoteInterface.test();
                } catch (RemoteException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

二、分析binder的源码
源码不多，先列出来，下面挨个方法写出了自己的理解

package com.example.zhaoziliang.rxjavaandretrofitdemo;
// Declare any non-default types here with import statements

public interface IRemoteInterface extends android.os.IInterface
{
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface
{
private static final java.lang.String DESCRIPTOR = "com.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface";
/** Construct the stub at attach it to the interface. */
public Stub()
{
this.attachInterface(this, DESCRIPTOR);
}
/**
 * Cast an IBinder object into an com.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface interface,
 * generating a proxy if needed.
 */
public static com.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface asInterface(android.os.IBinder obj)
{
if ((obj==null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin!=null)&&(iin instanceof com.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface))) {
return ((com.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface)iin);
}
return new com.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface.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_test:
{
data.enforceInterface(DESCRIPTOR);
this.test();
reply.writeNoException();
return true;
}
case TRANSACTION_add:
{
data.enforceInterface(DESCRIPTOR);
int _arg0;
_arg0 = data.readInt();
int _arg1;
_arg1 = data.readInt();
int _result = this.add(_arg0, _arg1);
reply.writeNoException();
reply.writeInt(_result);
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.example.zhaoziliang.rxjavaandretrofitdemo.IRemoteInterface
{
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 test() 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_test, _data, _reply, 0);
_reply.readException();
}
finally {
_reply.recycle();
_data.recycle();
}
}
@Override public int add(int a, int b) throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
int _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
_data.writeInt(a);
_data.writeInt(b);
mRemote.transact(Stub.TRANSACTION_add, _data, _reply, 0);
_reply.readException();
_result = _reply.readInt();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
/**
     * 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_test = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
static final int TRANSACTION_add = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
static final int TRANSACTION_basicTypes = (android.os.IBinder.FIRST_CALL_TRANSACTION + 2);
}
public void test() throws android.os.RemoteException;
public int add(int a, int b) throws android.os.RemoteException;
/**
     * 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;
}

1、attachInterface（value，key）
这个方法写在Stub()构造方法中，其实就是将本身的binder作为value，将DESCRIPTOR字符串作为key存起来了。
void attachInterface(IInterface plus, String descriptor)；
// 作用：
// 1. 将（descriptor，plus）作为（key,value）对存入到Binder对象中的一个Map<String,IInterface>对象中
// 2. 之后，Binder对象 可根据descriptor通过queryLocalIInterface（）获得对应IInterface对象（即plus）的引用，可依靠该引用完成对请求方法的调用
2、queryLocalInterface(String descriptor)
IInterface queryLocalInterface(String descriptor) ；
// 作用：根据 参数 descriptor 查找相应的IInterface对象（即plus引用）
3、asInterface
在client中IRemoteInterface.Stub.asInterface(binder)方法传入服务器端返回的IBinder对象，将IBinder对象传换成了IRemoteInterface接口对象
在server中返回的是biinder本身，在client中返回的是binder的代理对象
4、onTransact
进程2的client调用进程1的server的方法的时候，实际是在此方法中调用的
boolean onTransact(int code, Parcel data, Parcel reply, int flags)；
// 定义：继承自IBinder接口的
// 作用：执行Client进程所请求的目标方法（子类需要复写）
// 参数说明：
// code：Client进程请求方法标识符。即Server进程根据该标识确定所请求的目标方法
// data：目标方法的参数。（Client进程传进来的，此处就是整数a和b）
// reply：目标方法执行后的结果（返回给Client进程）
// 注：运行在Server进程的Binder线程池中；当Client进程发起远程请求时，远程请求会要求系统底层执行回调该方法
4、BinderProxy
final class BinderProxy implements IBinder {
// 即Server进程创建的Binder对象的代理对象类
// 该类属于Binder的内部类
}

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