Question: I'm trying to implement some automatic logout code for my Application on Android.

I need to detect if all the activities belonging to an Application have entered the background as opposed to working with `onPause()` and `onResume()` for each individual activity. iOS has a helpful `applicationDidEnterBackground:` method that I could utilize, but I'm unable to find a similar function in Android's `Application` class.

One approach seems to be to have an `AtomicInteger` counter and increment it once an activity becomes visible and decrement it when it's finished or onStop() gets called. So if the counter becomes zero, I can start a service that runs in the background and handles the logout. Is this how it's usually done?

Answer: 
You really don't want to log out the user when the "application" goes in the background, any more than you log out the user of a Web app when the user switches to another tab or minimizes their browser window for a moment. If you were to do either of those things in a Web app, your users would consider your Web app to be an epic fail. Similarly, if the user gets a phone call with a wrong number, or the alarm clock goes off, they'll be rather irritated with you if they have to immediately go back in and sign in when they were just using your app 5 seconds ago. Here, by "irritated", I mean one-star ratings on the Market and nasty comments.

A Web app automatic log out is based upon inactivity, using a server session cookie.

Similarly, when I build a secured Android app, I'll be implementing an inactivity-based mechanism, perhaps something like this:

Step #1: Create a `Session` class with a static singleton instance. The `Session` object holds the last-accessed timestamp.

Step #2: In each activity's `onResume()`, see if the `Session` singleton exists. If not, it's a brand-new process, so if this isn't the authentication activity, immediately do a `startActivity()` to bring up the authentication activity.

Step #3: Back in each activity's `onResume()`, if the `Session` object exists, call something like `extend()`. This would return a `boolean`, `true` indicating the session is still good (and the timestamp has been updated to now), `false` otherwise. If it returns `false`, do the same stuff as if the `Session` object were `null`.

Step #4: Your authentication activity, upon success, sets up the singleton `Session` object with the current timestamp.

Step #5: Your `Session` class' `extend()` method is where you make the determination if the session is too old.

No matter how the user gets into your application, if the session is too old (or it's a brand-new process), they are forced to authenticate. Yet, if the user briefly is interrupted -- where you and/or the user can define "briefly" -- they don't have to re-authenticate.
Create an Application class and include in the manifest 

```
<application
        android:name="com.example.hello.MyApplication"

public class MyApplication extends Application implements
        ActivityLifecycleCallbacks, ComponentCallbacks2 

```

override the following method

```
@Override
public void onTrimMemory(int level) {
        // this method is called when the app goes in background.
        // you can perform your logout service here
        super.onTrimMemory(level);
    }

```

this is valid of API level 14 and above.

You can even perform the the logout based on the amount of time the app is in background, which i would suggest is a better option. here is what you can do to create as "session timeout"

1. save the time stamp in `SharedPreferences` inside the `onTrimMemory(int level)` method
2. on all your activities onStrat() get the time stamp from sharedPref and compare it with current time. based on this you can perform a logout.
3. and clear the shared pref on onCreat of MyApplication