detect whether app is running in background or not.

import android.app.Activity;
import android.app.Application;
import android.os.Bundle;
import java.util.HashMap;
import timber.log.Timber;

/**
 * Check if the application is in the foreground or background.
 * *
 * Register this callbacks for an application
 * Application application = (Application) context.getApplicationContext();
 * application.registerActivityLifecycleCallbacks(new BaseLifeCycleCallbacks());
 * *
 * Note: These callbacks can be registered at any level of the application lifecycle.
 * Previous methods to get the application lifecycle forced the lifecycle callbacks to be registered
 * at the start of the application in a dedicated Application class.
 */
public class BaseLifeCycleCallbacks implements Application.ActivityLifecycleCallbacks {

    private static final String TAG = BaseLifeCycleCallbacks.class.getSimpleName();
    private HashMap<String, Integer> mActivities = null;

    public BaseLifeCycleCallbacks() {
        mActivities = new HashMap<String, Integer>();
    }

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

    @Override
    public void onActivityStarted(Activity activity) {
        //map Activity unique class name with 1 on foreground
        mActivities.put(activity.getLocalClassName(), 1);
        applicationStatus();
    }

    @Override
    public void onActivityResumed(Activity activity) {
    }

    @Override
    public void onActivityPaused(Activity activity) {
    }

    @Override
    public void onActivityStopped(Activity activity) {
        //map Activity unique class name with 0 on foreground
        mActivities.put(activity.getLocalClassName(), 0);
        applicationStatus();
    }

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

    }

    @Override
    public void onActivityDestroyed(Activity activity) {
    }

    /**
     * Check if any activity is in the foreground
     */
    private boolean isBackGround() {
        for (String s : mActivities.keySet()) {
            if (mActivities.get(s) == 1) {
                return false;
            }
        }
        return true;
    }

    /**
     * Returns application status.
     * @return  false if application is in background mode else return true.
     */
    public boolean applicationStatus() {
        try {
            boolean isInBackground = isBackGround();
            Timber.d(TAG + " %s ", "Is application running in background : " + isInBackground);
            return isInBackground;
        }catch (NullPointerException ex){

        }
        return false;
    }
}