本篇文章介绍如何通过App添加一个系统服务，服务端的App通过Android.mk编译进系统，来完成同Client端的跨进程通信。

（1）Server端

在服务端添加如下代码：

（A）服务回调的AIDL

// IDetonatorCallback.aidl
package com.detonator.server;interface IDetonatorCallback {void void onServerCallbackMessage(String msg);
}

（B）服务接口的AIDL

// IDetonatorService.aidl
package com.detonator.server;import com.detonator.server.IDetonatorCallback;interface IDetonatorService {void registerCallBack(IDetonatorCallback callback);void unregisterCallBack(IDetonatorCallback callback);int getScreenBrightness();boolean setScreenBrightness(int brightness);
}

（C）服务端Service的实现

package com.detonator.server;import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.os.RemoteCallbackList;
import android.os.RemoteException;
import android.provider.Settings;
import android.util.Log;public class DetonatorManagerService extends Service{private static final String TAG = "DetonatorManagerService";@Nullable@Overridepublic IBinder onBind(Intent intent) {return mDetonatorStub;}/*** AIDl 服务端声明实现*/private final IDetonatorService.Stub mDetonatorStub = new IDetonatorService.Stub() {@Overridepublic int getScreenBrightness() throws RemoteException {int result = -1;try {result = Settings.System.getInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS);} catch (Settings.SettingNotFoundException e) {e.printStackTrace();}Log.i(TAG, "getScreenBrightness =  " + result);return result;}@Overridepublic boolean setScreenBrightness(int brightness) throws RemoteException {Log.i(TAG, "setScreenBrightness_1 =  " + brightness);boolean optResult;// 自动亮度改为手动亮度try {int mode = Settings.System.getInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS_MODE);if (mode == Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC) {Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS_MODE,Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);}} catch (Settings.SettingNotFoundException e) {e.printStackTrace();}optResult = Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS, resultBrightness);Log.i(TAG, "setScreenBrightness_2 = " + brightness + " , optResult = " + optResult);return optResult;}@Overridepublic void registerCallBack(IDetonatorCallback callback) throws RemoteException {Log.i(TAG, "-- registerCallBack --");CallbackRegisterManager.getInstance().register(callback);}@Overridepublic void unregisterCallBack(IDetonatorCallback callback) throws RemoteException {Log.i(TAG, "-- unregisterCallBack --");CallbackRegisterManager.getInstance().unRegister(callback);}};@Overridepublic void noteClients(String msg) {RemoteCallbackList  remoteCallbackList = CallbackRegisterManager.getInstance().getRemoteCallbackList();int N = remoteCallbackList.beginBroadcast();for (int i = 0; i < N; i++) {try {IDetonatorCallback callback = remoteCallbackList.getBroadcastItem(i);callback.onMessageReceive(msg);} catch (RemoteException e) {e.printStackTrace();}}remoteCallbackList.finishBroadcast();}
}

（D）服务端Manager的实现

package com.detonator.server;import android.os.RemoteCallbackList;public class CallbackRegisterManager {private static CallbackRegisterManager instance;private RemoteCallbackList remoteCallbackList = null;private CallbackRegisterManager() {remoteCallbackList = new RemoteCallbackList<>();}public static CallbackRegisterManager getInstance() {synchronized (CallbackRegisterManager.class) {if (instance == null) {instance = new CallbackRegisterManager();}}return instance;}public RemoteCallbackList getRemoteCallbackList(){return remoteCallbackList;}public void register(IDetonatorCallback callback){if(remoteCallbackList != null){remoteCallbackList.register(callback);}}public void unRegister(IDetonatorCallback callback){if(remoteCallbackList != null){remoteCallbackList.unregister(callback);}}
}

（E）编译成服务APK

将如上代码编译成服务apk，通过Android.mk文件编译进系统。

//Android.mkLOCAL_PATH:= $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE := DetonatorServerLOCAL_MODULE_CLASS := APPS
LOCAL_MODULE_TAGS := optional
LOCAL_MODULE_SUFFIX := $(COMMON_ANDROID_PACKAGE_SUFFIX)
LOCAL_CERTIFICATE := platform
LOCAL_SRC_FILES := $(LOCAL_MODULE).apk
LOCAL_SYSTEM_EXT_MODULE := true
LOCAL_PRIVILEGED_MODULE := trueinclude $(BUILD_PREBUILT)

（2）Client端（应用）

将IDetonatorCallback.aidl和IDetonatorService.aidl拷贝到Client端。

（A）客户端Manager的实现

package com.detonator.server;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.util.Log;public class DetonatorManager {private static final String TAG = "DetonatorManager";private Context mContext;private static DetonatorManager mInstance;private IDetonatorService mService;private IBinder mBinder;private boolean mConnected;private RemoteCallbackImpl mRemoteCallbackImpl;private IRemoteCallback mRemoteCallback;public static DetonatorManager getInstance() {synchronized (DetonatorManager.class) {if (mInstance == null) {mInstance = new DetonatorManager();}}return mInstance;}public void init(Context context, IRemoteCallback iCallback){mContext = context.getApplicationContext();this.mRemoteCallback = iCallback;}public void register() {bindDetonatorManagerService(mConnService);}public void unRegister() {if (mConnected) {try {if (mRemoteCallbackImpl != null) {getService().unregisterCallBack(mRemoteCallbackImpl);}} catch (Exception e) {e.printStackTrace();}mContext.unbindService(conn);}}/*** AIDL 客户端连接器ServiceConnection实现，获取连接后的IBinder对象*/private ServiceConnection mConnService = new ServiceConnection() {@Overridepublic void onServiceConnected(ComponentName componentName, IBinder iBinder) {mBinder = iBinder;mConnected = true;// 初始化aidl远程回调mRemoteCallbackImpl = new RemoteCallbackImpl(mRemoteCallback);// 注册aidl远程回调try {getService().registerCallBack(mRemoteCallbackImpl);} catch (RemoteException e) {e.printStackTrace();}}@Overridepublic void onServiceDisconnected(ComponentName componentName) {mConnected = false;}};/*** 获取连接AIDL服务后的实例** @return*/private IDetonatorService getService() {if (mService != null) {return mService;}mService = IDetonatorService.Stub.asInterface(mBinder);return mService;}private boolean isServiceConnected() {return mConnected;}/* --------------------------------------------  以下是具体业务操作实现 -------------------------------------------- *//*** 获取屏幕亮度** @return 屏幕亮度值，由亮暗到亮[0-255]*/public int getScreenBrightness() {int result = -1;try {result = getService().getScreenBrightness();} catch (RemoteException e) {e.printStackTrace();}return result;}/*** 设置屏幕亮度** @return 屏幕亮度值，由亮暗到亮[0-255]*/public boolean setScreenBrightness(int brightness) {boolean optResult = true;try {optResult = getService().setScreenBrightness(brightness);} catch (RemoteException e) {optResult = false;e.printStackTrace();}return optResult;}
}

以上主要使用到如下类和接口。

package com.detonator.server;public interface IRemoteCallback {void  onReceiveMessage(String msg);
}

package com.detonator.server;
import android.os.RemoteException;public class RemoteCallbackImpl extends IDetonatorCallback.Stub {private static final String TAG = "DetonatorCallbackImpl";private IRemoteCallback mRemoteCallback = null;public RemoteCallbackImpl(IRemoteCallback iCallback) {this.mRemoteCallback = iCallback;}@Overridepublic void onServerCallbackMessage(String msg) throws RemoteException {if (mRemoteCallback != null) {mRemoteCallback.onReceiveMessage(msg);}}
}

上面的Manager是通过SDK的形式发布的，其Module Name是detonatorSDK，其build.gradle如下：

plugins {id 'com.android.library'
}android {namespace 'com.detonator.server'compileSdk 33//...}
}

（B）客户端App调用Manager的实现

package com.detonator.sample;import com.detonator.server.DetonatorManager;
import com.detonator.server.IRemoteCallback;public class MainActivity extends AppCompatActivity {private DetonatorManager mDetonatorManager;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mDetonatorManager = DetonatorManager.getInstance();mDetonatorManager.init(this, mReceiveMessage);mDetonatorManager.register();//通过Manager端调用远程服务的函数int brightness = mDetonatorManager.getScreenBrightness();mDetonatorManager.setScreenBrightness(brightness);}IRemoteCallback mReceiveMessage = new IRemoteCallback() {@Overridepublic void onReceiveMessage(String msg) {}};@Overrideprotected void onDestroy() {super.onDestroy();if (mDetonatorManager != null) {mDetonatorManager.unRegister();}}
}

通过aar包或者module引入来调用Manager相关方法。

plugins {id 'com.android.application'
}android {namespace 'com.detonator.sample'compileSdk 33//...
}dependencies {implementation project(path: ':detonatorSDK')//implementation(fileTree("libs/DetonatorSDK_v1.0.aar"))}

至此整个Client端通过AIDL调用远程服务流程全部结束。