Android 添加系统服务的方法详解

package com.example.utils;

import com.example.utils.IEventCallback;

interface ISystemEvent {
  void registerCallback(IEventCallback callback);

  void unregisterCallback(IEventCallback callback);

  void sendEvent(int type, String value);
}

package com.example.utils;

interface IEventCallback
{
  oneway void onSystemEvent(int type, String value);
}

LOCAL_SRC_FILES  = \
  core/java/android/view/IWindow.aidl \
  core/java/android/view/IWindowFocusObserver.aidl \
  core/java/android/view/IWindowId.aidl \
  部分代码省略 ...
  core/java/com/example/utils/ISystemEvent.aidl \
  core/java/com/example/utils/IEventCallback.aidl \
  部分代码省略 ...

package com.example.utils;

import android.content.Context;
import android.os.RemoteException;
import android.util.Log;

import com.example.example.ISystemEvent;
import com.example.IEventCallback;

public class SystemEventManager {

  private static final String TAG = SystemEventManager.class.getSimpleName();
  // 系统服务注册时使用的名字, 确保和已有的服务名字不冲突
  public static final String SERVICE = "test_systemevent";

  private final Context mContext;
  private final ISystemEvent mService;

  public SystemEventManager(Context context, ISystemEvent service) {
    mContext = context;
    mService = service;
    Log.d(TAG, "SystemEventManager init");
  }

  public void register(IEventCallback callback) {
    try {
      mService.registerCallback(callback);
    } catch (RemoteException e) {
      Log.w(TAG, "remote exception happen");
      e.printStackTrace();
    }
  }

  public void unregister(IEventCallback callback) {
    try {
      mService.unregisterCallback(callback);
    } catch (RemoteException e) {
      Log.w(TAG, "remote exception happen");
      e.printStackTrace();
    }
  }

  /**
   * Send event to SystemEventService.
   */
  public void sendEvent(int type, String value) {
    try {
      mService.sendEvent(type, value);
    } catch (RemoteException e) {
      Log.w(TAG, "remote exception happen");
      e.printStackTrace();
    }
  }
}

public SystemEventManager(Context context, ISystemEvent service)

package com.android.server.example;

import android.content.Context;
import android.os.Binder;
import android.os.RemoteCallbackList;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.util.Log;

import com.example.utils.ISystemEvent;
import com.example.utils.IEventCallback;

public class SystemEventService extends ISystemEvent.Stub {

  private static final String TAG = SystemEventService.class.getSimpleName();
  private RemoteCallbackList<IEventCallback> mCallbackList = new RemoteCallbackList<>();

  private Context mContext;

  public SystemEventService(Context context) {
    mContext = context;
    Log.d(TAG, "SystemEventService init");
  }

  @Override
  public void registerCallback(IEventCallback callback) {
    boolean result = mCallbackList.register(callback);
    Log.d(TAG, "register pid:"   Binder.getCallingPid()
          " uid:"   Binder.getCallingUid()   " result:"   result);

  }

  @Override
  public void unregisterCallback(IEventCallback callback) {
    boolean result = mCallbackList.unregister(callback);
    Log.d(TAG, "unregister pid:"   Binder.getCallingPid()
          " uid:"   Binder.getCallingUid()   " result:"   result);

  }

  @Override
  public void sendEvent(int type, String value) {
    sendEventToRemote(type, value   " remote");
  }

  public void sendEventToRemote(int type, String value) {
    int count = mCallbackList.getRegisteredCallbackCount();
    Log.d(TAG, "remote callback count:"   count);
    if (count > 0) {
      final int size = mCallbackList.beginBroadcast();
      for (int i = 0; i < size; i  ) {
        IEventCallback cb = mCallbackList.getBroadcastItem(i);
        try {
          if (cb != null) {
            cb.onSystemEvent(type, value);
          }
        } catch (RemoteException e) {
          e.printStackTrace();
          Log.d(TAG, "remote exception:"   e.getMessage());
        }
      }
      mCallbackList.finishBroadcast();
    }
  }
}

import com.android.server.example.SystemEventService;
import com.example.utils.SystemEventManager;

/**
 * Starts a miscellaneous grab bag of stuff that has yet to be refactored
 * and organized.
 */
private void startOtherServices() {
  // 部分代码省略...
  // start SystemEventService
  try {
    ServiceManager.addService(SystemEventManager.SERVICE,
          new SystemEventService(mSystemContext));
  } catch (Throwable e) {
    reportWtf("starting SystemEventService", e);
  }
  // 部分代码省略...
}

wifiscanner                u:object_r:wifiscanner_service:s0
wifi                   u:object_r:wifi_service:s0
window                  u:object_r:window_service:s0
# 部分代码省略...
test_systemevent             u:object_r:test_systemevent_service:s0
*                     u:object_r:default_android_service:s0

# 加入刚刚定义好的 test_systemevent_service 类型, 表明它是系统服务
type test_systemevent_service, system_api_service, system_server_service, service_manager_type;

context.getSystemService()

import com.example.utils.ISystemEvent;
import com.example.utils.SystemEventManager;

static { 
  // 部分代码省略, 参考其他代码, 注册Manger
  registerService(SystemEventManager.SERVICE, SystemEventManager.class,
      new CachedServiceFetcher<SystemEventManager>() {
    @Override
    public SystemEventManager createService(ContextImpl ctx) {
      // 获取服务
      IBinder b = ServiceManager.getService(SystemEventManager.SERVICE);
      // 转为 ISystemEvent
      ISystemEvent service = ISystemEvent.Stub.asInterface(b);
      return new SystemEventManager(ctx.getOuterContext(), service);
    }});
}

# 允许 untrusted_app 查找 test_systemevent_service
allow untrusted_app test_systemevent_service:service_manager find;

SystemEventManager eventManager = (SystemEventManager)
    context.getSystemService(SystemEventManager.SERVICE);

eventManager.register(eventCallback);

eventManager.unregister(eventCallback);

private IEventCallback.Stub eventCallback = new IEventCallback.Stub() {
  @Override
  public void onSystemEvent(int type, String value) throws RemoteException {
    Log.d("SystemEvent", "type:"   type   " value:"   value);
  }
};

eventManager.sendEvent(1, "test string");

// Initialize native services.
System.loadLibrary("android_servers");