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Android-Query (AQuery) is a light-weight library for doing asynchronous tasks and manipulating UI elements in Android. Our goal is to make Android coding simpler, easier, and more fun!

I’ve run into the following generalized question a lot recently: I have an event that occurs in the background. I want to update my activity, if the activity is on the screen. Otherwise, I want to raise a Notification.

Hence, the recipe for the activity-or-Notification pattern is: Define an action string you will use when the event occurs that you want to go to the activity or notification (e.g., com.commonsware.java.packages.are.fun.EVENT). Dynamically register a BroadcastReceiever in your activity, with an IntentFilter set up for the aforementioned action string and with a positive priority (the default priority for a filter is 0). This receiver should then have the activity do whatever it needs to do to update the UI based on this event. The receiver should also call abortBroadcast() to prevent others from getting it. Be sure to register the receiver in onStart() or onResume() and unregister the receiver in the corresponding onStop or onPause() method. Register in your manifest a BroadcastReceiver, with an <intent-filter> set up for the aforementioned action string. This receiver should raise the Notification. In your service (e.g., an IntentService), when the event occurs, call sendOrderedBroadcast(). And that’s it. If the activity is on-screen, its receiver will be registered, so it will get the event, process it, and cancel the broadcast. If the activity is not on-screen, its receiver will not be registered, so the event will go to the default handler, in the form of your manifest-registered BroadcastReceiver, which will raise the Notification.