正确的模式，以获取BroadcastReceiver中的WakeLock并在服务中释放它

Question

即使经过大量研究，我仍然不能完全确定如何实现一个由BroadcastReceiver启动的Service WakeLock的方式是正确的 - 即使它似乎工作正常。 广播接收器从警报发送到它的意图，所以从AlarmManager的API文档AlarmManager ：

如果您的警报接收器调用了Context.startService（），则手机可能会在启动所请求的服务之前休眠。 为了防止这种情况，您的BroadcastReceiver和服务需要实施单独的唤醒锁定策略，以确保电话继续运行，直到服务可用。

所以，在onReceive()我做：

    Intent serviceIntent = new Intent(context, SomeService.class);
    context.startService(serviceIntent);

    if(SomeService.wakeLock == null) {
        PowerManager powerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
        SomeService.wakeLock = powerManager.newWakeLock(
                PowerManager.PARTIAL_WAKE_LOCK, 
                SomeService.WAKE_LOCK_TAG);
    }
    if(! SomeService.wakeLock.isHeld()) {
        SomeService.wakeLock.acquire();
    }

在我做的服务中：

    try {
        // Do some work
    } finally {
        if(wakeLock != null) {
            if(wakeLock.isHeld()) {
                wakeLock.release();
            }
            wakeLock = null;
        }
    }

SomeService.wakeLock字段是包私有，静态和易失性。

我不确定的是使用isHeld()的检查 - 它是否真的告诉我是否获得了WakeLock ，我是否需要进行此检查？

Answer 1

我不确定的是使用isHeld()的检查 - 它是否真的告诉我是否获得了WakeLock ，我是否需要进行此检查？

实际上回答有些棘手。 在这里查看PowerManager和PowerManager.WakeLock的源代码， WakeLock.acquire()和WakeLock.acquireLocked()方法如下......

public void acquire(long timeout) {
    synchronized (mToken) {
        acquireLocked();
        mHandler.postDelayed(mReleaser, timeout);
    }
}

private void acquireLocked() {
    if (!mRefCounted || mCount++ == 0) {
        // Do this even if the wake lock is already thought to be held (mHeld == true)
        // because non-reference counted wake locks are not always properly released.
        // For example, the keyguard's wake lock might be forcibly released by the
        // power manager without the keyguard knowing.  A subsequent call to acquire
        // should immediately acquire the wake lock once again despite never having
        // been explicitly released by the keyguard.
        mHandler.removeCallbacks(mReleaser);
        try {
            mService.acquireWakeLock(mToken, mFlags, mTag, mWorkSource);
        } catch (RemoteException e) {
        }
        mHeld = true;
    }
}

... mService是一个IPowerManager接口，它的源代码不可用，因此在尝试调用acquireWakeLock(...)时很难分辨出可能出错或可能出现的错误。

在任何情况下，唯一可以捕获的异常是RemoteException ， catch块什么也不做。 在try / catch之后， mHeld都设置为true 。

简而言之，如果在acquire()之后立即调用isHeld() acquire() ，结果将始终为true 。

进一步查看PowerManager.WakeLock的源代码显示了release()类似行为，它调用release(int flags) ，无论发生什么， mHeld成员总是设置为false 。

总之，我建议检查isHeld()总是一个好主意，以便在以后版本的Android更改WakeLock方法的这种行为时作为最佳实践。

Answer 2

在单例内管理wakeLock（可通过所有上下文和对象访问的唯一实例）

使用自定义类的单例实例，然后您可以从调用到调用获取唤醒锁对象引用，

这里是一个单例的例子

class MyData {
   private static MyData mMydata= null; // unique reference ( singleton objet container)

   private PowerManager.Wakelock myobject = null; // inside the unique object container we have the unique working object to be use  by the application
   // can't make instance from outside... we want to have single instance
   // we want that outside use method "getInstance" to be able to use the object
   private MyData() {
   }

   // retrieve and/or create new unique instance
   public static MyData getInstance() {
     if (mMydata ==  null) mMyData = new MyData();
     return   mMyData;
   }

   // Works with your memory stored object
   // get...
   public PowerManager.WakeLock getMyWakelock() {
   return myobject;
   }
   // set ...
   public void setMyWakeLock(PowerManager.WakeLock obj) {
    myobject = obj;
   }
}

在您的应用程序中处理您的“wakelock”对象，您可以访问它

// set a created wakelock
MyData.getInstance().setMyWakeLock(wl);
// get the saved wakelock object
PowerManager.WakeLock obj =  MyData.getInstance().getMyWakeLock();

Answer 3

所有这些工作都可以通过一个名为WakefulBroadcastReceiver的帮助程序和本机类来完成

Answer 4

我认为android.os.Messenger可能是更好的方式

对于接收者：

public class MessengerReceiver extends BroadcastReceiver {


    private static final String TAG = "MessengerReceiver";

    private final MessengerHandler mHandler = new MessengerHandler();

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        mHandler.mWakeLock = ((PowerManager)context.getSystemService(Service.POWER_SERVICE)).newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "myreceiver");
        mHandler.mWakeLock.acquire();
        Log.e(TAG, "onReceive:: mHandler.mWakeLock=" + mHandler.mWakeLock + ", intent=" + intent + ", this=" + this);
        context.startService(new Intent(context, MessengerService.class).putExtra("messenger", new Messenger(mHandler)));
    }

    static class MessengerHandler extends Handler {

        WakeLock mWakeLock;
        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            if(mWakeLock != null){
                mWakeLock.release();
                Log.e(TAG, "handleMessage:mWakeLock=" + mWakeLock);
            }
            super.handleMessage(msg);
        }

    }
}

为服务：

public class MessengerService extends Service {
    private static final String TAG = "MessengerService";
    public MessengerService() {
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        // TODO Auto-generated method stub      
        Log.e(TAG, "onStartCommand:: intent=" + intent);
        final Messenger messenger = intent.getParcelableExtra("messenger");
        try {
            messenger.send(Message.obtain());
        } catch (RemoteException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return super.onStartCommand(intent, flags, startId);
    }
}

即使服务和接收器在不同的进程中运行，此方法也能正常工作。