背景

最近打算学习一下如何在framework层添加一个自定义service。
了解到自定义service需要使用aidl，为了加强对aidl的了解和使用过程，特意又温习了一下aidl的使用，并用博客的形式记录下来。
aidl官方参考：https://developer.android.google.cn/develop/background-work/services/aidl?hl=en

AIDL是什么

官方解释：Android 接口定义语言 (AIDL) 类似于其他 IDL：它允许您定义客户端和服务使用进程间通信 (IPC) 进行相互通信时都认可的编程接口。

定义 AIDL 接口

这里我使用的ide是Android Studio Iguana版本。
首先创建一个project，里面创建两个app一个叫client，另一个叫server。
在server app的src/main目录创建一个aidl文件IMyAidlInterface.aidl，内容如下

// IMyAidlInterface.aidl
package com.hai.server;
// Declare any non-default types here with import statements
//aidl说明参考：https://developer.android.google.cn/develop/background-work/services/aidl?hl=en
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);

    int getPid();

    oneway void getThreadId();
}

IMyAidlInterface.aidl中定义了三个接口供客户端调用。

然后编译一下project，就会在server的build目录下自动生成IMyAidlInterface.java接口文件，内容如下

/*
 * This file is auto-generated.  DO NOT MODIFY.
 */
package com.hai.server;
// Declare any non-default types here with import statements
//aidl说明参考：https://developer.android.google.cn/develop/background-work/services/aidl?hl=en
public interface IMyAidlInterface extends android.os.IInterface
{
  /** Default implementation for IMyAidlInterface. */
  public static class Default implements com.hai.server.IMyAidlInterface
  {
    /**
     * 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
    {
    }
    @Override public int getPid() throws android.os.RemoteException
    {
      return 0;
    }
    @Override public void getThreadId() throws android.os.RemoteException
    {
    }
    @Override
    public android.os.IBinder asBinder() {
      return null;
    }
  }
  /** Local-side IPC implementation stub class. */
  public static abstract class Stub extends android.os.Binder implements com.hai.server.IMyAidlInterface
  {
    /** Construct the stub at attach it to the interface. */
    public Stub()
    {
      this.attachInterface(this, DESCRIPTOR);
    }
    /**
     * Cast an IBinder object into an com.hai.server.IMyAidlInterface interface,
     * generating a proxy if needed.
     */
    public static com.hai.server.IMyAidlInterface asInterface(android.os.IBinder obj)
    {
      if ((obj==null)) {
        return null;
      }
      android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
      if (((iin!=null)&&(iin instanceof com.hai.server.IMyAidlInterface))) {
        return ((com.hai.server.IMyAidlInterface)iin);
      }
      return new com.hai.server.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
    {
      java.lang.String descriptor = DESCRIPTOR;
      if (code >= android.os.IBinder.FIRST_CALL_TRANSACTION && code <= android.os.IBinder.LAST_CALL_TRANSACTION) {
        data.enforceInterface(descriptor);
      }
      switch (code)
      {
        case INTERFACE_TRANSACTION:
        {
          reply.writeString(descriptor);
          return true;
        }
      }
      switch (code)
      {
        case TRANSACTION_basicTypes:
        {
          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();
          break;
        }
        case TRANSACTION_getPid:
        {
          int _result = this.getPid();
          reply.writeNoException();
          reply.writeInt(_result);
          break;
        }
        case TRANSACTION_getThreadId:
        {
          this.getThreadId();
          break;
        }
        default:
        {
          return super.onTransact(code, data, reply, flags);
        }
      }
      return true;
    }
    private static class Proxy implements com.hai.server.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);
          boolean _status = mRemote.transact(Stub.TRANSACTION_basicTypes, _data, _reply, 0);
          _reply.readException();
        }
        finally {
          _reply.recycle();
          _data.recycle();
        }
      }
      @Override public int getPid() 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);
          boolean _status = mRemote.transact(Stub.TRANSACTION_getPid, _data, _reply, 0);
          _reply.readException();
          _result = _reply.readInt();
        }
        finally {
          _reply.recycle();
          _data.recycle();
        }
        return _result;
      }
      @Override public void getThreadId() throws android.os.RemoteException
      {
        android.os.Parcel _data = android.os.Parcel.obtain();
        try {
          _data.writeInterfaceToken(DESCRIPTOR);
          boolean _status = mRemote.transact(Stub.TRANSACTION_getThreadId, _data, null, android.os.IBinder.FLAG_ONEWAY);
        }
        finally {
          _data.recycle();
        }
      }
    }
    static final int TRANSACTION_basicTypes = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
    static final int TRANSACTION_getPid = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
    static final int TRANSACTION_getThreadId = (android.os.IBinder.FIRST_CALL_TRANSACTION + 2);
  }
  public static final java.lang.String DESCRIPTOR = "com.hai.server.IMyAidlInterface";
  /**
   * 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;
  public int getPid() throws android.os.RemoteException;
  public void getThreadId() throws android.os.RemoteException;
}

IMyAidlInterface.java结构图

可以看到IMyAidlInterface.java也定义了和aidl相同的三个接口，并且定义了Default和Stub两个静态内部类去实现IMyAidlInterface接口。

• Default类默认空实现且没有继承Binder，实际无意义。
• Stub是一个继承Binder抽象类，实际是要在server端写一个Stub的实现类去实现实际的接口功能
• Stub.Proxy一般用于client端。

Server端实现服务

接下来就是在server端的service中实现aidl接口服务，这里我写了一个ServerService类，内容如下

package com.hai.server;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.os.RemoteException;
import android.os.SystemClock;
import android.system.Os;
import android.util.Log;

public class ServerService extends Service {
    private static final String TAG = "ServiceService";
    IMyAidlInterface.Stub binder = new IMyAidlInterface.Stub() {

        @Override
        public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, String aString) throws RemoteException {
            Log.d(TAG, "basicTypes() called with: anInt = [" + anInt + "], aLong = [" + aLong + "], aBoolean = [" + aBoolean + "], aFloat = [" + aFloat + "], aDouble = [" + aDouble + "], aString = [" + aString + "]");
        }

        @Override
        public int getPid() throws RemoteException {
            SystemClock.sleep(2000);
            return Os.getpid();
        }

        @Override
        public void getThreadId() throws RemoteException {
            SystemClock.sleep(2000);
        }
    };

    @Override
    public IBinder onBind(Intent intent) {
        Log.d(TAG, "onBind() called with: intent = [" + intent + "]");
        return binder;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        Log.d(TAG, "onUnbind() called with: intent = [" + intent + "]");
        return super.onUnbind(intent);
    }
}

为了client端可以通过隐式服务绑定服务，还需要在AndroidManifest.xml做一下配置

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android">
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.AidlDemo">
        <service
            android:name=".ServerService"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="com.hai.server.ServerService" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </service>
    </application>
</manifest>

当client端通过bindservice绑定成功后，服务端就会返回server端的binder对象给到client端。

Client端使用服务

首先需要把server端的aidl整个文件夹拷贝到client端的src目录，以便client端能够获得aidl的访问权限。client端的代码结构如图

编译一下project，就会在client的build目录下自动生成IMyAidlInterface.java接口文件。
接下来就是bindservice，bindservice服务成功后就可以获得binder的代理对象，进而调用aidl接口服务。如下是在activity中通过bindservice的方式调用aidl接口服务。

package com.hai.aidldemo;

import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.os.RemoteException;
import android.util.Log;
import android.view.View;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;

import com.hai.server.IMyAidlInterface;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    IMyAidlInterface myAidlInterface;
    ServiceConnection serviceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            Log.d(TAG, "onServiceConnected() called with: name = [" + name + "], service = [" + service + "]");
            myAidlInterface = IMyAidlInterface.Stub.asInterface(service);
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            Log.d(TAG, "onServiceDisconnected() called with: name = [" + name + "]");
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_main);
    }

    public void clk(View view) {
        switch (view.getId()) {
            case R.id.btn_bind:
                if (myAidlInterface == null) {
                    boolean b = bindService(new Intent("com.hai.server.ServerService").setPackage("com.hai.server"), serviceConnection, Context.BIND_AUTO_CREATE);
                    Log.d(TAG, "bindService: " + b);
                }
                break;
            case R.id.btn_unbind:
                if (myAidlInterface != null) {
                    unbindService(serviceConnection);
                }
                break;
            case R.id.btn_basicType:
                try {
                    myAidlInterface.basicTypes(1, 2, true, 4, 5, "6");
                } catch (RemoteException e) {
                    throw new RuntimeException(e);
                }
                break;
            case R.id.btn_getPid:
                try {
                    long start = System.currentTimeMillis();
                    int pid = myAidlInterface.getPid();
                    Log.d(TAG, "getPid: " + pid + ", cost:" + (System.currentTimeMillis() - start));
                } catch (RemoteException e) {
                    throw new RuntimeException(e);
                }
                break;
            case R.id.btn_getThreadId:
                try {
                    long start = System.currentTimeMillis();
                    myAidlInterface.getThreadId();
                    Log.d(TAG, "getThreadId: cost:" + (System.currentTimeMillis() - start));
                } catch (RemoteException e) {
                    throw new RuntimeException(e);
                }
                break;
        }
    }
}

项目源码：

https://gitee.com/menty/aidl-demo/blob/master/client/src/main/java/com/hai/aidldemo/MainActivity.java