RxAppState 
A simple, reactive Android library based on RxJava that monitors app state changes.
It notifies subscribers every time the app goes into background and comes back into foreground.
A typical use case is, for example, session tracking for analytics purposes or suppressing push notifications when the app is currently visible to the user.
Background
Android has this ancient pain of not providing any type of callback to know if your app is currently in the foreground or background. It is lacking an equivalent of the iOS UIApplicationDelegate which offers callbacks like applicationDidEnterBackground and applicationDidBecomeActive.
There are two popular discussions on this topic on StackOverflow:
- How to detect when an Android app goes to the background and come back to the foreground
- Checking if an Android application is running in the background
This library internally uses a combination of ActivityLifecycleCallbacks and the onTrimMemory(int level) callback to identify the current app state.
Just check out the source code (mainly: DefaultAppStateRecognizer). The implementation is dead simple.
Usage
You most probably want to monitor for app state changes in your application's onCreate() method in which case you also don't need to worry about unregistering your AppStateListener. Remember that if you subscribe in an Activity or a Fragment, don't forget to unsubscribe to avoid memory leaks.
AppStateMonitor appStateMonitor = RxAppStateMonitor.create(this);
appStateMonitor.addListener(new AppStateListener() {
@Override
public void onAppDidEnterForeground() {
// ...
}
@Override
public void onAppDidEnterBackground() {
// ...
}
}
);
appStateMonitor.start();
Example
Check out the sample project for an example implementation.
Download
Grab it via Gradle:
dependencies {
compile 'com.jenzz.appstate:appstate:3.0.1'
}
Note: There are adapters available for RxJava and RxJava2.
License
This project is licensed under the MIT License.