消息处理、工作线程的意外行为
我正在尝试一个带有后台服务的大型程序，并且正在使用基本的处理程序对象实现一个（相当不周密的）消息处理过程。该应用程序有一个主菜单，其中的按钮可启动 6 种不同的活动。
问题是这样的：如果我启动一个工作线程来启动对数据库的查询并检索一些数据，并且我关闭启动上述工作线程的活动，则活动中的处理程序仍然尝试运行并显示一个对话框，甚至尽管创建它的活动现在已完成（或未获得焦点）。在提交任何 (UI) 更改之前，如何判断当前活动是否处于焦点状态？
我最终通过简单地将“showDialog()”调用放在 try 语句中来解决了这个问题，但我想要一个更复杂的解决方案，因为这似乎是错误的做事方式。
I'm taking a stab at a large program with a background Service and I'm implementing a (rather poorly thought out) Message handling procedure using basic Handler objects. The application has a main menu with buttons which start 6 different activities.
Problem is this: if i start a worker thread which kicks off a query to the database and retrieves some data, and I close the Activity that started the aforementioned worker thread, the Handler in the Activity still tries to run and show a dialog, even though the Activity that created it is now finished (or not in focus). How can I tell whether the current Activity is in focus before committing any (UI) changes?
I ended up solving the issue by simply putting the 'showDialog()' call in a try statement, but i'd like a more sophisticated solution, as this just seems like the wrong way to do things.
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使用
sendBroadcast()，Activity通过中的并在registerReceiver()注册用于广播的BroadcastReceiveronResume()onPause()中取消注册。然后，它只会处理位于前台的事件。Use
sendBroadcast(), with theActivityregistering aBroadcastReceiverfor the broadcast viaregisterReceiver()inonResume()and unregistering it inonPause(). Then, it will only process the event if it is in the foreground.在启动线程的 Activity 的 onPause() 方法中放置一些标志，以指示它不再是前台。在
onStart()中反转标志。当需要显示对话框时，请选中此标志，并且仅在活动正在运行时才显示对话框。
Put some flag in
onPause()method of activity that starts the thread to indicate that it is not foreground anymore. InonStart()reverse the flag.When it is a time to display dialog, check this flag and only show dialog if activity is running.