Checking if an Android application is running in t

Question

By background, I mean none of the application's activities are currently visible to the user?

Answer 1

Since Android API 16 there is a simple way to check if app is in foreground. It may not be foolproof, but no methods on Android are foolproof. This method is good enough to use when your service receives update from server and has to decide whether to show notification, or not (because if UI is foreground, user will notice the update without notification).

RunningAppProcessInfo myProcess = new RunningAppProcessInfo();
ActivityManager.getMyMemoryState(myProcess);
isInBackground = myProcess.importance != RunningAppProcessInfo.IMPORTANCE_FOREGROUND;

Answer 2

There is no way, short of you tracking it yourself, to determine if any of your activities are visible or not. Perhaps you should consider asking a new StackOverflow question, explaining what it is you are trying to achieve from a user experience, so we can perhaps give you alternative implementation ideas.

Answer 3

In my opinion, many answers introduce a heavy load of code and bring lots of complexity and non-readability.

When people ask on SO how to communicate between a Service and a Activity, I usually advice to use the LocalBroadcastManager.

---

Why?

Well, by quoting the docs:

• You know that the data you are broadcasting won't leave your app, so don't need to worry about leaking private data.

• It is not possible for other applications to send these broadcasts to your app, so you don't need to worry about having security holes they can exploit.

• It is more efficient than sending a global broadcast through the system.

Not in the the docs:

• It does not require external libraries
• The code is minimal
• It's fast to implement and understand
• No custom self-implemented callbacks / ultra-singleton / intra-process pattern whatsoever...
• No strong references on Activity, Application, ...

---

Description

So, you want to check if any of the Activity is currently in the foreground. You usually do that in a Service, or your Application class.

This means, your Activity objects become the sender of a signal (I'm on / I'm off). Your Service, on the other hand, becomes the Receiver.

There are two moments in which your Activity tells you if it's going in the foreground or in the background (yes only two... not 6).

When the Activity goes into the foreground, the onResume() method is triggered (also called after onCreate()).

When the Activity goes in the back, onPause() is called.

These are the moments in which your Activity should send the signal to your Service to describe its state.

In case of multiple Activity's, remember the an Activity goes into the background first, then another one comes into the foreground.

So the situation would be:*

Activity1 -- send --> Signal:OFF
Activity2 -- send --> Signal:ON

The Service / Application will simply keep listening for those signals and act accordingly.

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Code (TLDR)

Your Service must implement a BroadcastReceiver in order to listen for signals.

this.localBroadcastReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        // received data if Activity is on / off
    }
}

public static final IntentFilter SIGNAL_FILTER = new IntentFilter("com.you.yourapp.MY_SIGNAL") 

Register the Receiver in Service::onCreate()

@Override
protected void onCreate() {
    LocalBroadcastManager.getInstance(getApplicationContext()).registerReceiver(this.localBroadcastReceiver, SIGNAL_FILTER);
}

Un-register it in Service::onDestroy()

@Override
protected void onDestroy() {
    // I'm dead, no need to listen to anything anymore.
    LocalBroadcastManager.getInstance(getApplicationContext()).unregisterReceiver(this.localBroadcastReceiver);
}

Now your Activity's must communicated their state.

In Activity::onResume()

Intent intent = new Intent();
intent.setAction(SomeActivity.SIGNAL_FILTER); // put ON boolean in intent    
LocalBroadcastManager.getInstance(getApplicationContext()).sendBroadcast(intent);

In Activity::onPause()

Intent intent = new Intent();
intent.setAction(SomeActivity.SIGNAL_FILTER); // put OFF boolean in intent    
LocalBroadcastManager.getInstance(getApplicationContext()).sendBroadcast(intent);

---

A very, very common situation

Developer: I want to send data from my Service and update the Activity. How do I check if the Activity is in the foreground?

There is usually no need to check if the Activity is in the foreground or not. Just send the data via LocalBroadcastManager from your Service. If the Activity is on, then it will respond and act.

For this very common situation, the Service becomes the sender, and the Activity implements the BroadcastReceiver.

So, create a Receiver in your Activity. Register it in onResume() and un-register it in onPause(). There is no need to use the other life-cycle methods.

Define the Receiver behavior in onReceive() (update ListView, do this, do that, ...).

This way the Activity will listen only if it's in the foreground and nothing will happen if it's in the back or is destroyed.

In case of multiple Activity's, whichever Activity is on will respond (if they also implement the Receiver).

If all are in the background, nobody will respond and the signal will simply get lost.

Send the data from the Service via Intent (see code above) by specifying the signal ID.

---

• Except for Multi-Window Support. It may be tricky (please test it if needed)...

Answer 4

DO NOT USE THIS ANSWER

user1269737's answer is the proper (Google/Android approved) way to do this. Go read their answer and give them a +1.

I'll leave my original answer here for posterity's sake. This was the best available back in 2012, but now Android has proper support for this.

Original answer

The key is using ActivityLifecycleCallbacks (note that this requires Android API level 14 (Android 4.0)). Just check if the number of stopped activities is equal to the number of started activities. If they're equal, your application is being backgrounded. If there are more started activities, your application is still visible. If there are more resumed than paused activities, your application is not only visible, but it's also in the foreground. There are 3 main states that your activity can be in, then: visible and in the foreground, visible but not in the foreground, and not visible and not in the foreground (i.e. in the background).

The really nice thing about this method is that it doesn't have the asynchronous issues getRunningTasks() does, but you also don't have to modify every Activity in your application to set/unset something in onResumed()/onPaused(). It's just a few lines of code that's self contained, and it works throughout your whole application. Plus, there are no funky permissions required either.

MyLifecycleHandler.java:

public class MyLifecycleHandler implements ActivityLifecycleCallbacks {
    // I use four separate variables here. You can, of course, just use two and
    // increment/decrement them instead of using four and incrementing them all.
    private int resumed;
    private int paused;
    private int started;
    private int stopped;

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
    }

    @Override
    public void onActivityDestroyed(Activity activity) {
    }

    @Override
    public void onActivityResumed(Activity activity) {
        ++resumed;
    }

    @Override
    public void onActivityPaused(Activity activity) {
        ++paused;
        android.util.Log.w("test", "application is in foreground: " + (resumed > paused));
    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
    }

    @Override
    public void onActivityStarted(Activity activity) {
        ++started;
    }

    @Override
    public void onActivityStopped(Activity activity) {
        ++stopped;
        android.util.Log.w("test", "application is visible: " + (started > stopped));
    }

    // If you want a static function you can use to check if your application is
    // foreground/background, you can use the following:
    /*
    // Replace the four variables above with these four
    private static int resumed;
    private static int paused;
    private static int started;
    private static int stopped;

    // And these two public static functions
    public static boolean isApplicationVisible() {
        return started > stopped;
    }

    public static boolean isApplicationInForeground() {
        return resumed > paused;
    }
    */
}

MyApplication.java:

// Don't forget to add it to your manifest by doing
// <application android:name="your.package.MyApplication" ...
public class MyApplication extends Application {
    @Override
    public void onCreate() {
        // Simply add the handler, and that's it! No need to add any code
        // to every activity. Everything is contained in MyLifecycleHandler
        // with just a few lines of code. Now *that's* nice.
        registerActivityLifecycleCallbacks(new MyLifecycleHandler());
    }
}

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@Mewzer has asked some good questions about this method that I'd like to respond to in this answer for everyone:

onStop() is not called in low memory situations; is that a problem here?

No. The docs for onStop() say:

Note that this method may never be called, in low memory situations where the system does not have enough memory to keep your activity's process running after its onPause() method is called.

The key here is "keep your activity's process running..." If this low memory situation is ever reached, your process is actually killed (not just your activity). This means that this method of checking for backgrounded-ness is still valid because a) you can't check for backgrounding anyway if your process is killed, and b) if your process starts again (because a new activity is created), the member variables (whether static or not) for MyLifecycleHandler will be reset to 0.

Does this work for configuration changes?

By default, no. You have to explicitly set configChanges=orientation|screensize (| with anything else you want) in your manifest file and handle the configuration changes, or else your activity will be destroyed and recreated. If you do not set this, your activity's methods will be called in this order: onCreate -> onStart -> onResume -> (now rotate) -> onPause -> onStop -> onDestroy -> onCreate -> onStart -> onResume. As you can see, there is no overlap (normally, two activities overlap very briefly when switching between the two, which is how this backgrounding-detection method works). In order to get around this, you must set configChanges so that your activity is not destroyed. Fortunately, I've had to set configChanges already in all of my projects because it was undesirable for my entire activity to get destroyed on screen rotate/resize, so I've never found this to be problematic. (thanks to dpimka for refreshing my memory on this and correcting me!)

One note:

When I've said "background" here in this answer, I've meant "your app is no longer visible." Android activities can be visible yet not in the foreground (for example, if there's a transparent notification overlay). That's why I've updated this answer to reflect that.

It's important to know that Android has a weird limbo moment when switching activities where nothing is in the foreground. For this reason, if you check if your application is in the foreground when switching between activities (in the same app), you'll be told you're not in the foreground (even though your app is still the active app and is visible).

You can check if your app is in the foreground in your Activity's onPause() method after super.onPause(). Just remember the weird limbo state I just talked about.

You can check if your app is visible (i.e. if it's not in the background) in your Activity's onStop() method after super.onStop().

Answer 5

The best solution I have come up with uses timers.

You have start a timer in onPause() and cancel the same timer in onResume(), there is 1 instance of the Timer (usually defined in the Application class). The timer itself is set to run a Runnable after 2 seconds (or whatever interval you think is appropriate), when the timer fires you set a flag marking the application as being in the background.

In the onResume() method before you cancel the timer, you can query the background flag to perform any startup operations (e.g. start downloads or enable location services).

This solution allows you to have several activities on the back stack, and doesn't require any permissions to implement.

This solution works well if you use an event bus too, as your timer can simply fire an event and various parts of your app can respond accordingly.

Answer 6

I did my own implementation of ActivityLifecycleCallbacks. I'm using SherlockActivity, but for normal Activity class might work.

First, I'm creating an interface that have all methods for track the activities lifecycle:

public interface ActivityLifecycleCallbacks{
    public void onActivityStopped(Activity activity);
    public void onActivityStarted(Activity activity);
    public void onActivitySaveInstanceState(Activity activity, Bundle outState);
    public void onActivityResumed(Activity activity);
    public void onActivityPaused(Activity activity);
    public void onActivityDestroyed(Activity activity);
    public void onActivityCreated(Activity activity, Bundle savedInstanceState);
}

Second, I implemented this interface in my Application's class:

public class MyApplication extends Application implements my.package.ActivityLifecycleCallbacks{

    @Override
    public void onCreate() {
        super.onCreate();           
    }

    @Override
    public void onActivityStopped(Activity activity) {
        Log.i("Tracking Activity Stopped", activity.getLocalClassName());

    }

    @Override
    public void onActivityStarted(Activity activity) {
        Log.i("Tracking Activity Started", activity.getLocalClassName());

    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
        Log.i("Tracking Activity SaveInstanceState", activity.getLocalClassName());
    }

    @Override
    public void onActivityResumed(Activity activity) {
        Log.i("Tracking Activity Resumed", activity.getLocalClassName());
    }

    @Override
    public void onActivityPaused(Activity activity) {
        Log.i("Tracking Activity Paused", activity.getLocalClassName());
    }

    @Override
    public void onActivityDestroyed(Activity activity) {
        Log.i("Tracking Activity Destroyed", activity.getLocalClassName());
    }

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        Log.i("Tracking Activity Created", activity.getLocalClassName());
    }
}

Third, I'm creating a class that extends from SherlockActivity:

public class MySherlockActivity extends SherlockActivity {

    protected MyApplication nMyApplication;

    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        nMyApplication = (MyApplication) getApplication();
        nMyApplication.onActivityCreated(this, savedInstanceState);
    }

    protected void onResume() {
        // TODO Auto-generated method stub
        nMyApplication.onActivityResumed(this);
        super.onResume();

    }

    @Override
    protected void onPause() {
        // TODO Auto-generated method stub
        nMyApplication.onActivityPaused(this);
        super.onPause();
    }

    @Override
    protected void onDestroy() {
        // TODO Auto-generated method stub
        nMyApplication.onActivityDestroyed(this);
        super.onDestroy();
    }

    @Override
    protected void onStart() {
        nMyApplication.onActivityStarted(this);
        super.onStart();
    }

    @Override
    protected void onStop() {
        nMyApplication.onActivityStopped(this);
        super.onStop();
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        nMyApplication.onActivitySaveInstanceState(this, outState);
        super.onSaveInstanceState(outState);
    }   
}

Fourth, all class that extend from SherlockActivity, I replaced for MySherlockActivity:

public class MainActivity extends MySherlockActivity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

}

Now, in the logcat you will see the logs programmed in the Interface implementation made in MyApplication.