Android Framework层Binder机制

Framework层Binder相关接口：

---

IInterface接口：

public interface IInterface
{
    /**
     * Retrieve the Binder object associated with this interface.
     * You must use this instead of a plain cast, so that proxy objects
     * can return the correct result.
     */
    public IBinder asBinder();
}

IBinder接口：

public interface IBinder {
  
    public String getInterfaceDescriptor() throws RemoteException;

    public boolean pingBinder();

    public boolean isBinderAlive();
    
    public IInterface queryLocalInterface(String descriptor);

    public void shellCommand(FileDescriptor in, FileDescriptor out, FileDescriptor err,
            String[] args, ShellCallback shellCallback, ResultReceiver resultReceiver) throws RemoteException;

    public interface DeathRecipient {
        public void binderDied();
    }

    public void linkToDeath(DeathRecipient recipient, int flags)
            throws RemoteException;

    public boolean unlinkToDeath(DeathRecipient recipient, int flags);
}

AIDL简易示例：

---

aidl-example-structure.png

IMainInterface.aidl代码：

package com.afollestad.aidlexample;
import com.afollestad.aidlexample.MainObject;

interface IMainService {
    MainObject[] listFiles(String path);

    void exit();
}

MainObject.aidl代码：

package com.afollestad.aidlexample;
parcelable MainObject;

MainObject.java代码：

public class MainObject implements Parcelable {

    private String mPath;

    public MainObject(Parcel source) {
        mPath = source.readString();
    }

    public MainObject(String path) {
        mPath = path;
    }

    public String getPath() {
        return mPath;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(mPath);
    }

    public static final Parcelable.Creator<MainObject> CREATOR = new Parcelable.Creator<MainObject>() {
        @Override
        public MainObject[] newArray(int size) {
            return new MainObject[size];
        }

        @Override
        public MainObject createFromParcel(Parcel source) {
            return new MainObject(source);
        }
    };
}

MainService.java代码：

public class MainService extends Service {

   // 省略...

    private final IMainService.Stub mBinder = new IMainService.Stub() {
        @Override
        public MainObject[] listFiles(String path) throws RemoteException {
            log("Received list command for: " + path);
            List<MainObject> toSend = new ArrayList<>();
            // Generates a list of 1000 objects that aren't sent back to the binding Activity
            for (int i = 0; i < 1000; i++) {
                toSend.add(new MainObject("/example/item" + (i + 1)));
            }
            return toSend.toArray(new MainObject[toSend.size()]);
        }

        @Override
        public void exit() throws RemoteException {
            log("Received exit command.");
            stopSelf();
        }
    };
}

编译之后，产生的aidl接口文件路径：

IMainService-build-path.png

其代码结构：

AIDL-build.png

IMainInterface.java详细代码：

/*
 * This file is auto-generated.  DO NOT MODIFY.
 * Original file: /home/bianjp/repos/android/hotfix/aidl-example/receiver/src/main/aidl/com/afollestad/aidlexample/IMainService.aidl
 */
package com.afollestad.aidlexample;

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

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

        /**
         * Cast an IBinder object into an com.afollestad.aidlexample.IMainService interface,
         * generating a proxy if needed.
         */
        public static com.afollestad.aidlexample.IMainService asInterface(android.os.IBinder obj) {
            if ((obj == null)) {
                return null;
            }
            android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
            if (((iin != null) && (iin instanceof com.afollestad.aidlexample.IMainService))) {
                return ((com.afollestad.aidlexample.IMainService) iin);
            }
            return new com.afollestad.aidlexample.IMainService.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_listFiles: {
                    data.enforceInterface(DESCRIPTOR);
                    java.lang.String _arg0;
                    _arg0 = data.readString();
                    com.afollestad.aidlexample.MainObject[] _result = this.listFiles(_arg0);
                    reply.writeNoException();
                    reply.writeTypedArray(_result, android.os.Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
                    return true;
                }
                case TRANSACTION_exit: {
                    data.enforceInterface(DESCRIPTOR);
                    this.exit();
                    reply.writeNoException();
                    return true;
                }
            }
            return super.onTransact(code, data, reply, flags);
        }

        private static class Proxy implements com.afollestad.aidlexample.IMainService {
            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 com.afollestad.aidlexample.MainObject[] listFiles(java.lang.String path) throws android.os.RemoteException {
                android.os.Parcel _data = android.os.Parcel.obtain();
                android.os.Parcel _reply = android.os.Parcel.obtain();
                com.afollestad.aidlexample.MainObject[] _result;
                try {
                    _data.writeInterfaceToken(DESCRIPTOR);
                    _data.writeString(path);
                    mRemote.transact(Stub.TRANSACTION_listFiles, _data, _reply, 0);
                    _reply.readException();
                    _result = _reply.createTypedArray(com.afollestad.aidlexample.MainObject.CREATOR);
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }
                return _result;
            }

            @Override
            public void exit() 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_exit, _data, _reply, 0);
                    _reply.readException();
                } finally {
                    _reply.recycle();
                    _data.recycle();
                }
            }
        }

        static final int TRANSACTION_listFiles = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
        static final int TRANSACTION_exit = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
    }

    public com.afollestad.aidlexample.MainObject[] listFiles(java.lang.String path) throws android.os.RemoteException;

    public void exit() throws android.os.RemoteException;
}

附上一张Framework层Binder通信模型图：图片来源

app_binder_demo.jpg

手写Binder示例

---

binder-framework-demo.png

IMyService.java代码：

/**
 * 作为接口
 */
public interface IMyService extends IInterface {
    static final java.lang.String DESCRIPTOR = "com.yuanhh.frameworkBinder.MyServer";
    public void sayHello(String str) throws RemoteException ;
    static final int TRANSACTION_say = android.os.IBinder.FIRST_CALL_TRANSACTION;
}

MyServicce.java代码：

import android.os.Binder;
import android.os.IBinder;
import android.os.Parcel;
import android.os.RemoteException;

public class MyService extends Binder implements IMyService{ 
    

    public MyService() {
        this.attachInterface(this, DESCRIPTOR);
    }

    @Override
    public IBinder asBinder() {
        return this;
    }

    /** 将MyService转换为IMyService接口 **/
    public static com.yuanhh.frameworkBinder.IMyService asInterface(
            android.os.IBinder obj) {
        if ((obj == null)) {
            return null;
        }
        android.os.IInterface iInterface = obj.queryLocalInterface(DESCRIPTOR);
        if (((iInterface != null) && (iInterface instanceof com.yuanhh.frameworkBinder.IMyService))) {
            return ((com.yuanhh.frameworkBinder.IMyService) iInterface);
        }
        return null;
    }

    /**  服务端，接收远程消息，处理onTransact方法  **/
    @Override
    protected boolean onTransact(int code, Parcel data, Parcel reply, int flags)
            throws RemoteException {
        switch (code) {
        case INTERFACE_TRANSACTION: {
            reply.writeString(DESCRIPTOR);
            return true;
        }
        case TRANSACTION_say: {
            data.enforceInterface(DESCRIPTOR);
            String str = data.readString();
            sayHello(str);
            reply.writeNoException();
            return true;
        }
        }
        return super.onTransact(code, data, reply, flags);
    }

    /** 自定义sayHello()方法   **/
    @Override
    public void sayHello(String str) {
        System.out.println("MyService:: Hello, " + str);
    }
}

ServiceProxy.java代码：

import android.os.IBinder;
import android.os.RemoteException;

public class MyServiceProxy implements IMyService {
    private android.os.IBinder mRemote;  //´ú±íBpBinder

    public MyServiceProxy(android.os.IBinder remote) {
        mRemote = remote;
    }

    public java.lang.String getInterfaceDescriptor() {
        return DESCRIPTOR;
    }

    @Override
    public void sayHello(String str) throws RemoteException {
        android.os.Parcel _data = android.os.Parcel.obtain();
        android.os.Parcel _reply = android.os.Parcel.obtain();
        try {
            _data.writeInterfaceToken(DESCRIPTOR);
            _data.writeString(str);
            mRemote.transact(TRANSACTION_say, _data, _reply, 0);
            _reply.readException();
        } finally {
            _reply.recycle();
            _data.recycle();
        }
    }

    @Override
    public IBinder asBinder() {
        return mRemote;
    }

}

ServerDemo.java:

import android.os.Looper;
import android.os.ServiceManager;

public class ServerDemo {

    public static void main(String[] args) {
        System.out.println("MyService Start");
        Looper.prepareMainLooper(); //开启循环执行
        android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_FOREGROUND); //设置为前台优先级
        ServiceManager.addService("MyService", new MyService());//注册服务
        Looper.loop();
    }

}

ClientDemo.java代码：

import android.os.IBinder;
import android.os.RemoteException;
import android.os.ServiceManager;

public class ClientDemo {
 
    public static void main(String[] args) throws RemoteException {
        System.out.println("Client start");
        IBinder binder = ServiceManager.getService("MyService"); //获取名为"MyService"的服务
        IMyService myService = new MyServiceProxy(binder); //创建MyServiceProxy对象
        myService.sayHello("binder"); //通过MyServiceProxy对象调用接口的方法
        System.out.println("Client end");
    }
}

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