Binder系列之AIDL的使用

AIDL是Android进程IPC定义语言的缩写，主要是用来定义进程间通信的接口。本文使用一个Demo程序来说明AIDL的使用，demo工程的分2个module:

1. App "客户端"，发送网络请求到server端，并且在接收到来自于server的数据后展示结果到UI。
2. Server "服务端"负责执行耗时的网络请求。

以上2个module运行于2个独立的进程当中，进程间的通信依靠aidl接口。

Server

首先，所有的aidl接口都由server端定义，目录结构如下：

server的文件结构

我们服务进程需要提供一个访问入口给客户进程，所以首先定义了IPostInterface.aidl，内容如下：

Paste_Image.png

post方法接受一个Request请求，setResponseInterface接受一个访问客户进程的接口，该接口是用于上报网络任务的结果给客户进程的。
因为使用了自定义类Request，所以我们需要创建一个aidl文件，用于声明Request，如下 aidl文件名要和Request相同:

Paste_Image.png

接下来，还需要实现Request，Request必须实现Parcelable接口，如下:

package www.seven.com.server;

import android.os.Parcel;
import android.os.Parcelable;

/**
 * @author Seven in 2017-01-07
 */

public class Request implements Parcelable {

    public void setRequestId(int requestId) {
        this.mRequestId = requestId;
    }

    public void setUrl(String url) {
        this.mUrl = url;
    }

    public int getRequestId() {
        return mRequestId;
    }

    public String getUrl() {
        return mUrl;
    }

    // 请求的唯一id
    private int mRequestId;

    // 请求的url
    private String mUrl;

    protected Request(Parcel in) {
        mUrl = in.readString();
        mRequestId = in.readInt();
    }

    public Request(int reqId, String url) {
        mRequestId = reqId;
        mUrl = url;
    }

    public static final Creator<Request> CREATOR = new Creator<Request>() {
        @Override
        public Request createFromParcel(Parcel in) {
            return new Request(in);
        }

        @Override
        public Request[] newArray(int size) {
            return new Request[size];
        }
    };

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

    @Override
    public void writeToParcel(Parcel parcel, int i) {
        parcel.writeString(mUrl);
        parcel.writeInt(mRequestId);
    }
}

上面的实现过程，都是模板代码来的，值得注意的地方是从Parcel里面读取数据的顺序，也和写入数据的顺序一致。

setResponseInterface需要提交一个aidl接口给服务进程，好让服务进程能够及时反馈网络请求的结果，改aidl接口定义如下:

Paste_Image.png

该接口接受成功和失败的消息，当网络任务执行成功时，需要返回一个Response实例给客户进程，类似Request，我们也需要定义Response的aidl声明：

// Response.aidl
package www.seven.com.server;

parcelable Response;

同样，我们也需要实现Response类：

package www.seven.com.server;

import android.os.Parcel;
import android.os.Parcelable;

/**
 * @author Seven in 2017-01-07
 */

public class Response implements Parcelable {

    // 这个应答对应的请求。
    private Request mRequest;

    private int mStatusCode;

    private String mResponseStr;

    public Request getRequest() {
        return mRequest;
    }

    public int getStatusCode() {
        return mStatusCode;
    }

    public String getResponseStr() {
        return mResponseStr;
    }

    protected Response(Parcel in) {
        mRequest = in.readParcelable(getClass().getClassLoader());
        mStatusCode = in.readInt();
        mResponseStr = in.readString();
    }

    public Response(Request request, int code, String resStr) {
        mRequest = request;
        mStatusCode = code;
        mResponseStr = resStr;
    }

    public static final Creator<Response> CREATOR = new Creator<Response>() {
        @Override
        public Response createFromParcel(Parcel in) {
            return new Response(in);
        }

        @Override
        public Response[] newArray(int size) {
            return new Response[size];
        }
    };

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

    @Override
    public void writeToParcel(Parcel parcel, int i) {
        parcel.writeParcelable(mRequest, i);
        parcel.writeInt(mStatusCode);
        parcel.writeString(mResponseStr);
    }
}

因为一个Response会保存着一个对应的Request，所以这里需要注意下载Parcelable里面读写另外一个Parcelable的实现方式。

接下来是网络任务的实现，在这里，执行网络请求，可以使用第三方库，也可以使用系统API实现，我现在只是模拟一个耗时任务而已。NetworkTask实现如下，该Task接受一个Request，并将结果提交给Handler。

package www.seven.com.server.services;

import android.os.AsyncTask;
import android.os.Handler;
import android.os.Message;
import android.util.Log;

import java.lang.ref.WeakReference;

import www.seven.com.server.Request;
import www.seven.com.server.Response;

/**
 * @author Seven in 2017-01-07
 */

public class NetworkTask extends AsyncTask<Request, Integer, Response> {

    private WeakReference<Handler> mWeakRef;

    public NetworkTask(Handler receiver) {
        mWeakRef = new WeakReference<Handler>(receiver);
    }

    @Override
    protected Response doInBackground(Request... requests) {
        Log.d("SevenThread", "[NetworkTask] Current Thread " + Thread.currentThread().getId());
        Response response = null;
        if (requests[0].getRequestId() % 3 == 0) {
            // 失败的情况
            postFailure(requests[0].getRequestId(), requests[0].getUrl() + "'s response Fail !!!!");

        } else {
            // 成功的情况
            response = new Response(requests[0], 200, requests[0].getUrl() + "'s response");
        }
        return response;
    }

    @Override
    protected void onPostExecute(Response response) {
        if (response != null) {
            postSuccess(response);
        }
    }

    private void postSuccess(Response response) {
        Handler handler = mWeakRef.get();
        if (handler != null) {
            handler.obtainMessage(NetworkService.RESPONSE_SUCCESS, response).sendToTarget();

        }
    }

    private void postFailure(int reqId, String msg) {
        Handler handler = mWeakRef.get();
        if (handler != null) {
            Message message = handler.obtainMessage(NetworkService.RESPONSE_FIAL);
            message.arg1 = reqId;
            message.obj = msg;
            message.sendToTarget();
        }
    }
}

该Handler来自于NetwokService，NetworkService的实现如下：

package www.seven.com.server.services;

import android.app.Service;
import android.content.Intent;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.RemoteException;
import android.support.annotation.Nullable;
import android.util.Log;

import java.security.PublicKey;

import www.seven.com.server.IPostInterface;
import www.seven.com.server.IResponseInterface;
import www.seven.com.server.Request;
import www.seven.com.server.Response;

/**
 * @author Seven in 2017-01-07
 */

public class NetworkService extends Service {

    public static final int RESPONSE_SUCCESS = 0;
    public static final int RESPONSE_FIAL    = 1;

    private IResponseInterface mIResponseInterface;

    private NetworkResponseHandler mNetworkResponseHandler = new NetworkResponseHandler();

    private IPostInterface mPostInterface = new IPostInterface.Stub() {

        @Override
        public void setResponseInterface(IResponseInterface responseInterface) throws RemoteException {
            mIResponseInterface = responseInterface;
        }

        @Override
        public boolean post(Request request) throws RemoteException {
            Log.d("SevenThread", "[NetworkService] Current Thread " + Thread.currentThread().getId());
            new NetworkTask(mNetworkResponseHandler).execute(request);
            return true;
        }
    };
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return mPostInterface.asBinder();
    }

    private class NetworkResponseHandler extends Handler {

        @Override
        public void handleMessage(Message msg) {

            switch (msg.what) {
                case RESPONSE_SUCCESS:
                    handleSuccess((Response) msg.obj);
                    break;
                case RESPONSE_FIAL:
                    handleFailure(msg.arg1, (String) msg.obj);
                    break;
            }
        }
    }

    private void handleSuccess(Response response) {
        if (mIResponseInterface != null) {
            try {
                mIResponseInterface.onResponseSuccess(response.getRequest().getRequestId(), response);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }
    }

    private void handleFailure(int reqId, String msg) {
        if (mIResponseInterface != null) {
            try {
                mIResponseInterface.onResponseFailure(reqId, msg);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }
    }
}

NetworkService的具体工作是：接受一个Request，创建一个NetworkTask，执行完毕后，返回给客户进程。

Client

客户端比较简单，就一个ClientActivity，具体实现如下：

package www.seven.com.aidldemo;

import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.IBinder;
import android.os.RemoteException;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import www.seven.com.server.IPostInterface;
import www.seven.com.server.IResponseInterface;
import www.seven.com.server.Request;
import www.seven.com.server.Response;
import www.seven.com.server.services.NetworkService;

public class ClientActivity extends AppCompatActivity {

    private static int REQ_CODE = 0;


    private IResponseInterface mIResponseInterface = new IResponseInterface.Stub() {

        @Override
        public void onResponseSuccess(final int requestId, final Response response) throws RemoteException {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    mResponseSb.append("request " + requestId + " " + response.getResponseStr() + "\n");
                    mResponseTv.setText(mResponseSb.toString());
                }
            });
        }

        @Override
        public void onResponseFailure(final int requestId, final String msg) throws RemoteException {
            // aidl回调是在独立的线程执行,所以需要在ui线程更新
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    mResponseSb.append("request " + requestId + " " + msg + "\n");
                    mResponseTv.setText(mResponseSb.toString());
                }
            });
        }
    };

    private IPostInterface mIPostInterface;

    private StringBuilder mResponseSb = new StringBuilder();

    private TextView mResponseTv;

    private ServiceConnection mServiceConnection;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_client);

        mResponseTv = (TextView) findViewById(R.id.response);
    }

    public void onSend(View view) {

        int reqId = REQ_CODE++;
        Request request = new Request(reqId, "request " + reqId);

        mResponseSb.append("request " + reqId + "\n");
        mResponseTv.setText(mResponseSb.toString());

        if (mIPostInterface == null) {
            Intent service = new Intent(this, NetworkService.class);
            mServiceConnection = new ServerConnection(request);
            bindService(service, mServiceConnection, Context.BIND_AUTO_CREATE);
        } else {
            try {
                mIPostInterface.post(request);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }
    }

    private class ServerConnection implements ServiceConnection {

        private Request mRequest;

        public ServerConnection(Request request) {
            mRequest = request;
        }

        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            mIPostInterface = IPostInterface.Stub.asInterface(iBinder);

            try {
                mIPostInterface.setResponseInterface(mIResponseInterface);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
            try {
                mIPostInterface.post(mRequest);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {
            mIPostInterface = null;
            mServiceConnection = null;
        }
    }

    @Override
    protected void onDestroy() {
        unbindService(mServiceConnection);
        super.onDestroy();
    }
}

需要注意的点是：在第一次发送请求时，会先进行服务绑定；IResponseInterface接收到消息时，需要在将更新view的操作放到ui线程中，因为aidl的回调是在独立非UI线程中的。

最后，需要在manifest文件中声明NetworkService运行在独立的进程中：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="www.seven.com.aidldemo">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name="www.seven.com.aidldemo.ClientActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <service android:name="www.seven.com.server.services.NetworkService"
            android:process=":networking"
            />
    </application>

</manifest>