在任何应用程序活动中，Android从后台线程显示对话框

Question

I tried to look clear answer for it but wasn't able to find it anywhere. I am running background thread in main activity that checks for certain variable and if it is true it should show alert dialog. I also want this dialog to show up on any focused activity of the application. I tried it by adding Looper.prepare() and Looper.loop() to the thread but it does not work properly and it affects while() loop that I use to check variable in that thread. Can anyone please help me in finding out what is the best way to implement this?

Thanks.

Answer 1

If you construct the background thread using the main/ui thread, you can create a Handler in the constructor. When you want to run some code on the main/ui thread, you simply Handler.post(Runnable r) with a runnable to the ui thread.

If your background thread is not being constructed on the ui/main thread, you can use a BroadcastIntent to and a BroadcastReceiver pattern to send messages between your background thread and your foreground activities. This is especially useful if you are switching foreground activities during the useful life of your background thread.

Answer 2

Ok, i can see two approaches. The first one is a dirty but quick: You can extend TimerTask and Handler classes. YourTimerTask will check variable and send a Message to YourHandler . YourHandler should override handleMessage and show a dialog.

The second one might be an overkill, but still. Android is event-based . It means that system gives you an opportunity to create your own events and handle it. So, you can start a Service , which will check your variable and send a Broadcast (can be local). In your activity you have to create your own BroadcastReceiver and register it. This receiver will handle a message.

Answer 3

You may want to try creating an implementation of Runnable and passing that to a View 's post() method.

final Runnable r = new Runnable() {
    public void run() {
        //code to display dialog
    }
}

final View view = findViewById(R.id.XYZ);
view.post(r);

This will run the Runnable on the UI thread.