By background, I mean none of the application's activities are currently visible to the user?
This question is related to
android
None of the answers quite fitted the specific case if you're looked to know if a specfic activity is in the forground and if you're an SDK without direct access to the Application. For me I was in background thread having just recieved a push notification for a new chat message and only want to display a system notification if the chat screen isn't in the foreground.
Using the ActivityLifecycleCallbacks that as been recommended in other answers I've created a small util class that houses the logic to whether MyActivity is in the Foreground or not.
class MyActivityMonitor(context: Context) : Application.ActivityLifecycleCallbacks {
private var isMyActivityInForeground = false
init {
(context.applicationContext as Application).registerActivityLifecycleCallbacks(this)
}
fun isMyActivityForeground() = isMyActivityInForeground
override fun onActivityPaused(activity: Activity?) {
if (activity is MyActivity) {
isMyActivityInForeground = false
}
}
override fun onActivityResumed(activity: Activity?) {
if (activity is MyActivity) {
isMyActivityInForeground = true
}
}
}
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.
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());
}
}
@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().
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:
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.
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
Serviceand update theActivity. How do I check if theActivityis 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.
fun isAppInForeground(): Boolean {
val activityManager = getSystemService(Context.ACTIVITY_SERVICE) as ActivityManager ?: return false
val appProcesses = activityManager.runningAppProcesses ?: return false
val packageName = packageName
for (appProcess in appProcesses) {
if (appProcess.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND && appProcess.processName == packageName) {
return true
}
}
return false
}
This code will check foreground and background in any condition:
Java Code:
private static boolean isApplicationForeground(Context context) {
KeyguardManager keyguardManager =
(KeyguardManager) context.getSystemService(Context.KEYGUARD_SERVICE);
if (keyguardManager.isKeyguardLocked()) {
return false;
}
int myPid = Process.myPid();
ActivityManager activityManager =
(ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
List<ActivityManager.RunningAppProcessInfo> list;
if ((list = activityManager.getRunningAppProcesses()) != null) {
for (ActivityManager.RunningAppProcessInfo aList : list) {
ActivityManager.RunningAppProcessInfo info;
if ((info = aList).pid == myPid) {
return info.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND;
}
}
}
return false;
}
Kotlin Code:
private fun isApplicationForeground(context: Context): Boolean {
val keyguardManager = context.getSystemService(Context.KEYGUARD_SERVICE) as KeyguardManager
if (keyguardManager.isKeyguardLocked) {
return false
}
val myPid = Process.myPid()
val activityManager = context.getSystemService(Context.ACTIVITY_SERVICE) as ActivityManager
var list: List<ActivityManager.RunningAppProcessInfo>
if (activityManager.runningAppProcesses.also { list = it } != null) {
for (aList in list) {
var info: ActivityManager.RunningAppProcessInfo
if (aList.also { info = it }.pid == myPid) {
return info.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND
}
}
}
return false
}
What about using getApplicationState().isInForeground() ?
Since it isn't already mentioned, I will suggest the readers to explore ProcessLifecycleOwner available through Android Architecture components
It might be too late to answer but if somebody comes visiting then here is the solution I suggest, The reason(s) an app wants to know it's state of being in background or coming to foreground can be many, a few are, 1. To show toasts and notifications when the user is in BG. 2.To perform some tasks for the first time user comes from BG, like a poll, redraw etc.
The solution by Idolon and others takes care of the first part, but does not for the second. If there are multiple activities in your app, and the user is switching between them, then by the time you are in second activity, the visible flag will be false. So it cannot be used deterministically.
I did something what was suggested by CommonsWare, "If the Service determines that there are no activities visible, and it remains that way for some amount of time, stop the data transfer at the next logical stopping point."
The line in bold is important and this can be used to achieve second item. So what I do is once I get the onActivityPaused() , don not change the visible to false directly, instead have a timer of 3 seconds (that is the max that the next activity should be launched), and if there is not onActivityResumed() call in the next 3 seconds, change visible to false. Similarly in onActivityResumed() if there is a timer then I cancel it. To sum up,the visible becomes isAppInBackground.
Sorry cannot copy-paste the code...
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.
Building on @Cornstalks answer to include a couple of useful features.
Extra features:
App.java
public class App extends Application {
@Override
public void onCreate() {
super.onCreate();
registerActivityLifecycleCallbacks(AppLifecycleHandler.getInstance());
}
}
AppLifecycleHandler.java
public class AppLifecycleHandler implements Application.ActivityLifecycleCallbacks {
private int resumed;
private int started;
private final String DebugName = "AppLifecycleHandler";
private boolean isVisible = false;
private boolean isInForeground = false;
private static AppLifecycleHandler instance;
public static AppLifecycleHandler getInstance() {
if (instance == null) {
instance = new AppLifecycleHandler();
}
return instance;
}
private AppLifecycleHandler() {
}
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
}
@Override
public void onActivityDestroyed(Activity activity) {
}
@Override
public void onActivityResumed(Activity activity) {
++resumed;
android.util.Log.w(DebugName, "onActivityResumed -> application is in foreground: " + (resumed > 0) + " (" + activity.getClass() + ")");
setForeground((resumed > 0));
}
@Override
public void onActivityPaused(Activity activity) {
--resumed;
android.util.Log.w(DebugName, "onActivityPaused -> application is in foreground: " + (resumed > 0) + " (" + activity.getClass() + ")");
setForeground((resumed > 0));
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
}
@Override
public void onActivityStarted(Activity activity) {
++started;
android.util.Log.w(DebugName, "onActivityStarted -> application is visible: " + (started > 0) + " (" + activity.getClass() + ")");
setVisible((started > 0));
}
@Override
public void onActivityStopped(Activity activity) {
--started;
android.util.Log.w(DebugName, "onActivityStopped -> application is visible: " + (started > 0) + " (" + activity.getClass() + ")");
setVisible((started > 0));
}
private void setVisible(boolean visible) {
if (isVisible == visible) {
// no change
return;
}
// visibility changed
isVisible = visible;
android.util.Log.w(DebugName, "App Visiblility Changed -> application is visible: " + isVisible);
// take some action on change of visibility
}
private void setForeground(boolean inForeground) {
if (isInForeground == inForeground) {
// no change
return;
}
// in foreground changed
isInForeground = inForeground;
android.util.Log.w(DebugName, "App In Foreground Changed -> application is in foreground: " + isInForeground);
// take some action on change of in foreground
}
public static boolean isApplicationVisible() {
return AppLifecycleHandler.getInstance().started > 0;
}
public static boolean isApplicationInForeground() {
return AppLifecycleHandler.getInstance().resumed > 0;
}
}
If you turn on developer settings "Don't keep actvities" - check only count of created activites is not enough. You must check also isSaveInstanceState. My custom method isApplicationRunning() check is android app is running:
Here my work code:
public class AppLifecycleService implements Application.ActivityLifecycleCallbacks {
private int created;
private boolean isSaveInstanceState;
private static AppLifecycleService instance;
private final static String TAG = AppLifecycleService.class.getName();
public static AppLifecycleService getInstance() {
if (instance == null) {
instance = new AppLifecycleService();
}
return instance;
}
public static boolean isApplicationRunning() {
boolean isApplicationRunning = true;
if (getCountCreatedActvities() == 0 && !isSaveInstanceState()) {
isApplicationRunning = false;
}
return isApplicationRunning;
}
public static boolean isSaveInstanceState() {
return AppLifecycleService.getInstance().isSaveInstanceState;
}
public static int getCountCreatedActvities() {
return AppLifecycleService.getInstance().created;
}
private AppLifecycleService() {
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
this.isSaveInstanceState = true;
}
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
++created;
}
@Override
public void onActivityDestroyed(Activity activity) {
--created;
}
@Override
public void onActivityResumed(Activity activity) { }
@Override
public void onActivityPaused(Activity activity) { }
@Override
public void onActivityStarted(Activity activity) { }
@Override
public void onActivityStopped(Activity activity) { }
}
In my activities onResume and onPause I write an isVisible boolean to SharedPrefences.
SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(this);
Editor editor = sharedPrefs.edit();
editor.putBoolean("visible", false);
editor.commit();
And read it elsewhere when needed via,
// Show a Toast Notification if App is not visible (ie in background. Not running, etc)
SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(context);
if(!sharedPrefs.getBoolean("visible", true)){...}
Maybe not elegant, but it works for me...
See the comment in the onActivityDestroyed function.
Works with SDK target version 14> :
import android.app.Activity;
import android.app.Application;
import android.os.Bundle;
import android.util.Log;
public class AppLifecycleHandler implements Application.ActivityLifecycleCallbacks {
public static int active = 0;
@Override
public void onActivityStopped(Activity activity) {
Log.i("Tracking Activity Stopped", activity.getLocalClassName());
active--;
}
@Override
public void onActivityStarted(Activity activity) {
Log.i("Tracking Activity Started", activity.getLocalClassName());
active++;
}
@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());
active++;
}
@Override
public void onActivityPaused(Activity activity) {
Log.i("Tracking Activity Paused", activity.getLocalClassName());
active--;
}
@Override
public void onActivityDestroyed(Activity activity) {
Log.i("Tracking Activity Destroyed", activity.getLocalClassName());
active--;
// if active var here ever becomes zero, the app is closed or in background
if(active == 0){
...
}
}
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
Log.i("Tracking Activity Created", activity.getLocalClassName());
active++;
}
}
The system distinguishes between foreground and background apps. (The definition of background for purposes of service limitations is distinct from the definition used by memory management; an app might be in the background as pertains to memory management, but in the foreground as pertains to its ability to launch services.) An app is considered to be in the foreground if any of the following is true:
If none of those conditions is true, the app is considered to be in the background.
You should use a shared preference to store the property and act upon it using service binding from your activities. If you use binding only, (that is never use startService), then your service would run only when you bind to it, (bind onResume and unbind onPause) that would make it run on foreground only, and if you do want to work on background you can use the regular start stop service.
Starting support library version 26 you can use ProcessLifecycleOwner, just add it to your dependency like described here, for example:
dependencies {
def lifecycle_version = "1.1.1"
// ViewModel and LiveData
implementation "android.arch.lifecycle:extensions:$lifecycle_version"
// alternatively - Lifecycles only (no ViewModel or LiveData).
// Support library depends on this lightweight import
implementation "android.arch.lifecycle:runtime:$lifecycle_version"
annotationProcessor "android.arch.lifecycle:compiler:$lifecycle_version" // use kapt for Kotlin
}
And then just query ProcessLifecycleOwner whenever you want for app state, examples:
// Check if app is in background
ProcessLifecycleOwner.get().getLifecycle().getCurrentState() == Lifecycle.State.CREATED;
// Check if app is in foreground
ProcessLifecycleOwner.get().getLifecycle().getCurrentState().isAtLeast(Lifecycle.State.STARTED);
Activity gets paused when a Dialog comes above it so all the recommended solutions are half-solutions. You need to create hooks for dialogs as well.
I think this question should be more clear. When? Where? What is your specific situation you want to konw if your app is in background?
I just introduce my solution in my way.
I get this done by using the field "importance" of RunningAppProcessInfo class in every activity's onStop method in my app, which can be simply achieved by providing a BaseActivity for other activities to extend which implements the onStop method to check the value of "importance". Here is the code:
public static boolean isAppRunning(Context context) {
ActivityManager activityManager = (ActivityManager) context
.getSystemService(Context.ACTIVITY_SERVICE);
List<RunningAppProcessInfo> appProcesses = activityManager
.getRunningAppProcesses();
for (RunningAppProcessInfo appProcess : appProcesses) {
if (appProcess.processName.equals(context.getPackageName())) {
if (appProcess.importance != RunningAppProcessInfo.IMPORTANCE_PERCEPTIBLE) {
return true;
}
}
}
return false;
}
Another solution for this old post (for those that it might help) :
<application android:name=".BaseApplication" ... >
public class BaseApplication extends Application {
private class Status {
public boolean isVisible = true;
public boolean isFocused = true;
}
private Map<Activity, Status> activities;
@Override
public void onCreate() {
activities = new HashMap<Activity, Status>();
super.onCreate();
}
private boolean hasVisibleActivity() {
for (Status status : activities.values())
if (status.isVisible)
return true;
return false;
}
private boolean hasFocusedActivity() {
for (Status status : activities.values())
if (status.isFocused)
return true;
return false;
}
public void onActivityCreate(Activity activity, boolean isStarting) {
if (isStarting && activities.isEmpty())
onApplicationStart();
activities.put(activity, new Status());
}
public void onActivityStart(Activity activity) {
if (!hasVisibleActivity() && !hasFocusedActivity())
onApplicationForeground();
activities.get(activity).isVisible = true;
}
public void onActivityWindowFocusChanged(Activity activity, boolean hasFocus) {
activities.get(activity).isFocused = hasFocus;
}
public void onActivityStop(Activity activity, boolean isFinishing) {
activities.get(activity).isVisible = false;
if (!isFinishing && !hasVisibleActivity() && !hasFocusedActivity())
onApplicationBackground();
}
public void onActivityDestroy(Activity activity, boolean isFinishing) {
activities.remove(activity);
if(isFinishing && activities.isEmpty())
onApplicationStop();
}
private void onApplicationStart() {Log.i(null, "Start");}
private void onApplicationBackground() {Log.i(null, "Background");}
private void onApplicationForeground() {Log.i(null, "Foreground");}
private void onApplicationStop() {Log.i(null, "Stop");}
}
public class MyActivity extends BaseActivity {...}
public class BaseActivity extends Activity {
private BaseApplication application;
@Override
protected void onCreate(Bundle state) {
application = (BaseApplication) getApplication();
application.onActivityCreate(this, state == null);
super.onCreate(state);
}
@Override
protected void onStart() {
application.onActivityStart(this);
super.onStart();
}
@Override
public void onWindowFocusChanged(boolean hasFocus) {
application.onActivityWindowFocusChanged(this, hasFocus);
super.onWindowFocusChanged(hasFocus);
}
@Override
protected void onStop() {
application.onActivityStop(this, isFinishing());
super.onStop();
}
@Override
protected void onDestroy() {
application.onActivityDestroy(this, isFinishing());
super.onDestroy();
}
}
GOOGLE SOLUTION - not a hack, like previous solutions. Use ProcessLifecycleOwner
Kotlin:
class ArchLifecycleApp : Application(), LifecycleObserver {
override fun onCreate() {
super.onCreate()
ProcessLifecycleOwner.get().lifecycle.addObserver(this)
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
fun onAppBackgrounded() {
//App in background
}
@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun onAppForegrounded() {
// App in foreground
}
}
Java:
public class ArchLifecycleApp extends Application implements LifecycleObserver {
@Override
public void onCreate() {
super.onCreate();
ProcessLifecycleOwner.get().getLifecycle().addObserver(this);
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
public void onAppBackgrounded() {
//App in background
}
@OnLifecycleEvent(Lifecycle.Event.ON_START)
public void onAppForegrounded() {
// App in foreground
}
}
in app.gradle
dependencies {
...
implementation "android.arch.lifecycle:extensions:1.1.0"
//New Android X dependency is this -
implementation "androidx.lifecycle:lifecycle-extensions:2.0.0"
}
allprojects {
repositories {
...
google()
jcenter()
maven { url 'https://maven.google.com' }
}
}
You can read more about Lifecycle related architecture components here - https://developer.android.com/topic/libraries/architecture/lifecycle
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.
Idolon's answer is error prone and much more complicated althought repeatead here check android application is in foreground or not? and here Determining the current foreground application from a background task or service
There is a much more simpler approach:
On a BaseActivity that all Activities extend:
protected static boolean isVisible = false;
@Override
public void onResume()
{
super.onResume();
setVisible(true);
}
@Override
public void onPause()
{
super.onPause();
setVisible(false);
}
Whenever you need to check if any of your application activities is in foreground just check isVisible();
To understand this approach check this answer of side-by-side activity lifecycle: Activity side-by-side lifecycle
There are few ways to detect whether your application is running in the background, but only one of them is completely reliable:
The right solution (credits go to Dan, CommonsWare and NeTeInStEiN)
Track visibility of your application by yourself using Activity.onPause, Activity.onResume methods. Store "visibility" status in some other class. Good choices are your own implementation of the Application or a Service (there are also a few variations of this solution if you'd like to check activity visibility from the service).
Example
Implement custom Application class (note the isActivityVisible() static method):
public class MyApplication extends Application {
public static boolean isActivityVisible() {
return activityVisible;
}
public static void activityResumed() {
activityVisible = true;
}
public static void activityPaused() {
activityVisible = false;
}
private static boolean activityVisible;
}
Register your application class in AndroidManifest.xml:
<application
android:name="your.app.package.MyApplication"
android:icon="@drawable/icon"
android:label="@string/app_name" >
Add onPause and onResume to every Activity in the project (you may create a common ancestor for your Activities if you'd like to, but if your activity is already extended from MapActivity/ListActivity etc. you still need to write the following by hand):
@Override
protected void onResume() {
super.onResume();
MyApplication.activityResumed();
}
@Override
protected void onPause() {
super.onPause();
MyApplication.activityPaused();
}
Update
ActivityLifecycleCallbacks were added in API level 14 (Android 4.0). You can use them to track whether an activity of your application is currently visible to the user. Check Cornstalks' answer below for the details.
The wrong one
I used to suggest the following solution:
You can detect currently foreground/background application with
ActivityManager.getRunningAppProcesses()which returns a list ofRunningAppProcessInforecords. To determine if your application is on the foreground checkRunningAppProcessInfo.importancefield for equality toRunningAppProcessInfo.IMPORTANCE_FOREGROUNDwhileRunningAppProcessInfo.processNameis equal to your application package name.Also if you call
ActivityManager.getRunningAppProcesses()from your application UI thread it will return importanceIMPORTANCE_FOREGROUNDfor your task no matter whether it is actually in the foreground or not. Call it in the background thread (for example viaAsyncTask) and it will return correct results.
While this solution may work (and it indeed works most of the time) I strongly recommend to refrain from using it. And here's why. As Dianne Hackborn wrote:
These APIs are not there for applications to base their UI flow on, but to do things like show the user the running apps, or a task manager, or such.
Yes there is a list kept in memory for these things. However, it is off in another process, managed by threads running separately from yours, and not something you can count on (a) seeing in time to make the correct decision or (b) have a consistent picture by the time you return. Plus the decision about what the "next" activity to go to is always done at the point where the switch is to happen, and it is not until that exact point (where the activity state is briefly locked down to do the switch) that we actually know for sure what the next thing will be.
And the implementation and global behavior here is not guaranteed to remain the same in the future.
I wish I had read this before I posted an answer on the SO, but hopefully it's not too late to admit my error.
Another wrong solution
Droid-Fu library mentioned in one of the answers uses ActivityManager.getRunningTasks for its isApplicationBroughtToBackground method. See Dianne's comment above and don't use that method either.
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;
You can use ComponentCallbacks2 to detect if the app is in background. BTW this callback is only available in API Level 14 (Ice Cream Sandwich) and above.
You will get a call to the method:
public abstract void onTrimMemory (int level)
if the level is ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN then the app is in background.
You can implement this interface to an activity, service, etc.
public class MainActivity extends AppCompatActivity implements ComponentCallbacks2 {
@Override
public void onConfigurationChanged(final Configuration newConfig) {
}
@Override
public void onLowMemory() {
}
@Override
public void onTrimMemory(final int level) {
if (level == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) {
// app is in background
}
}
}
The only one correct solution:
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
MyApp.mainActivity = this;
super.onCreate(savedInstanceState);
...
}
public class MyApp extends Application implements LifecycleObserver {
public static MainActivity mainActivity = null;
@Override
public void onCreate() {
super.onCreate();
ProcessLifecycleOwner.get().getLifecycle().addObserver(this);
}
@OnLifecycleEvent(Lifecycle.Event.ON_STOP)
void onAppBackgrounded() {
// app in background
if (mainActivity != null) {
...
}
}
@OnLifecycleEvent(Lifecycle.Event.ON_START)
void onAppForegrounded() {
// app in foreground
if (mainActivity != null) {
...
}
}
}
I tried the recommended solution that uses Application.ActivityLifecycleCallbacks and many others, but they didn't work as expected. Thanks to Sarge, I came up with a pretty easy and straightforward solution that I am describing below.
They key of the solution is the fact of understanding that if we have ActivityA and ActivityB, and we call ActivityB from ActivityA (and not call
ActivityA.finish), then ActivityB'sonStart()will be called before ActivityAonStop().
That's also the main difference between onStop() and onPause() that none did mention in the articles I read.
So based on this Activity's Lifecycle behavior, you can simply count how many times did onStart() and onPause() got called in your program. Note that for each Activity of your program, you must override onStart() and onStop(), in order to increment/decrement the static variable used for counting. Below is the code implementing this logic. Note that I am using a class that extends Application, so dont forget to declare on Manifest.xml inside Application tag: android:name=".Utilities", although it can be implemented using a simple custom class too.
public class Utilities extends Application
{
private static int stateCounter;
public void onCreate()
{
super.onCreate();
stateCounter = 0;
}
/**
* @return true if application is on background
* */
public static boolean isApplicationOnBackground()
{
return stateCounter == 0;
}
//to be called on each Activity onStart()
public static void activityStarted()
{
stateCounter++;
}
//to be called on each Activity onStop()
public static void activityStopped()
{
stateCounter--;
}
}
Now on each Activity of our program, we should override onStart() and onStop() and increment/decrement as shown below:
@Override
public void onStart()
{
super.onStart();
Utilities.activityStarted();
}
@Override
public void onStop()
{
Utilities.activityStopped();
if(Utilities.isApplicationOnBackground())
{
//you should want to check here if your application is on background
}
super.onStop();
}
With this logic, there are 2 possible cases:
stateCounter = 0 : The number of stopped is equal with the number of started Activities, which means that the application is running on the background.stateCounter > 0 : The number of started is bigger than the number of stopped, which means that the application is running on the foreground.Notice: stateCounter < 0 would mean that there are more stopped Activities rather than started, which is impossible. If you encounter this case, then it means that you are not increasing/decreasing the counter as you should.
You are ready to go. You should want to check if your application is on background inside onStop().
To piggyback on what CommonsWare and Key have said, you could perhaps extend the Application class and have all of your activities call that on their onPause/onResume methods. This would allow you to know which Activity(ies) are visible, but this could probably be handled better.
Can you elaborate on what you have in mind exactly? When you say running in the background do you mean simply having your application still in memory even though it is not currently on screen? Have you looked into using Services as a more persistent way to manage your app when it is not in focus?
I recommend reading through this page: http://developer.android.com/reference/android/app/Activity.html
In short, your activity is no longer visible after onStop() has been called.
I would like to recommend you to use another way to do this.
I guess you want to show start up screen while the program is starting, if it is already running in backend, don't show it.
Your application can continuously write current time to a specific file. While your application is starting, check the last timestamp, if current_time-last_time>the time range your specified for writing the latest time, it means your application is stopped, either killed by system or user himself.
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.
Source: Stackoverflow.com