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How to get current foreground activity context in android?


Question

Whenever my broadcast is executed I want to show alert to foreground activity.

2019/01/17
1
173
1/17/2019 3:34:27 PM

Accepted Answer

Knowing that ActivityManager manages Activity, so we can gain information from ActivityManager. We get the current foreground running Activity by

ActivityManager am = (ActivityManager)context.getSystemService(Context.ACTIVITY_SERVICE);
ComponentName cn = am.getRunningTasks(1).get(0).topActivity;

UPDATE 2018/10/03
getRunningTasks() is DEPRECATED. see the solutions below.

This method was deprecated in API level 21. As of Build.VERSION_CODES.LOLLIPOP, this method is no longer available to third party applications: the introduction of document-centric recents means it can leak person information to the caller. For backwards compatibility, it will still return a small subset of its data: at least the caller's own tasks, and possibly some other tasks such as home that are known to not be sensitive.

2018/10/08
39
10/8/2018 3:47:55 AM


I expand on the top of @gezdy's answer.

In every Activities, instead of having to "register" itself with Application with manual coding, we can make use of the following API since level 14, to help us achieve similar purpose with less manual coding.

public void registerActivityLifecycleCallbacks (Application.ActivityLifecycleCallbacks callback)

http://developer.android.com/reference/android/app/Application.html#registerActivityLifecycleCallbacks%28android.app.Application.ActivityLifecycleCallbacks%29

In Application.ActivityLifecycleCallbacks, you can get which Activity is "attached" to or "detached" to this Application.

However, this technique is only available since API level 14.

2015/04/22

Update 2: There is an official api added for this, please use ActivityLifecycleCallbacks instead.

UPDATE:

As pointed by @gezdy, and I'm grateful for that. set reference to null too for current activity, instead of updating on just every onResume set it to null on every Activity's onDestroy to avoid memory leak problem.

A while ago I needed the same functionality and here is the method how I achieved this. In your every activity override these life cycle methods.

@Override
protected void onResume() {
    super.onResume();
    appConstantsObj.setCurrentActivity(this);

}

@Override
protected void onPause() {
   clearReferences();
   super.onPause();
}

@Override
protected void onDestroy() {        
   clearReferences();
   super.onDestroy();
}

private void clearReferences(){
          Activity currActivity = appConstantsObj.getCurrentActivity();
          if (this.equals(currActivity))
                appConstantsObj.setCurrentActivity(null);
}

Now in your broadcast class you can access current activity to show alert on it.

2018/02/12

@lockwobr Thanks for update

This does not work 100% of the time in api version 16, if you read the code on github the function "currentActivityThread" was change in Kitkat, so I want to say version 19ish, kind of hard to match api version to releases in github.

Having access to the current Activity is very handy. Wouldn’t it be nice to have a static getActivity method returning the current Activity with no unnecessary questions?

The Activity class is very useful. It gives access to the application’s UI thread, views, resources, and many more. Numerous methods require a Context, but how to get the pointer? Here are some ways:

  • Tracking the application’s state using overridden lifecycle methods. You have to store the current Activity in a static variable and you need access to the code of all Activities.
  • Tracking the application’s state using Instrumentation. Declare Instrumentation in the manifest, implement it and use its methods to track Activity changes. Passing an Activity pointer to methods and classes used in your Activities. Injecting the pointer using one of the code injection libraries. All of these approaches are rather inconvenient; fortunately, there is a much easier way to get the current Activity.
  • Seems like the system needs access to all Activities without the issues mentioned above. So, most likely there is a way to get Activities using only static calls. I spent a lot of time digging through the Android sources on grepcode.com, and I found what I was looking for. There is a class called ActivityThread. This class has access to all Activities and, what’s even better, has a static method for getting the current ActivityThread. There is only one little problem – the Activity list has package access.

Easy to solve using reflection:

public static Activity getActivity() {
    Class activityThreadClass = Class.forName("android.app.ActivityThread");
    Object activityThread = activityThreadClass.getMethod("currentActivityThread").invoke(null);
    Field activitiesField = activityThreadClass.getDeclaredField("mActivities");
    activitiesField.setAccessible(true);

    Map<Object, Object> activities = (Map<Object, Object>) activitiesField.get(activityThread);
    if (activities == null)
        return null;

    for (Object activityRecord : activities.values()) {
        Class activityRecordClass = activityRecord.getClass();
        Field pausedField = activityRecordClass.getDeclaredField("paused");
        pausedField.setAccessible(true);
        if (!pausedField.getBoolean(activityRecord)) {
            Field activityField = activityRecordClass.getDeclaredField("activity");
            activityField.setAccessible(true);
            Activity activity = (Activity) activityField.get(activityRecord);
            return activity;
        }
    }

    return null;
}

Such a method can be used anywhere in the app and it’s much more convenient than all of the mentioned approaches. Moreover, it seems like it’s not as unsafe as it looks. It doesn’t introduce any new potential leaks or null pointers.

The above code snippet lacks exception handling and naively assumes that the first running Activity is the one we’re looking for. You might want to add some additional checks.

Blog Post

2017/07/18

I did the Following in Kotlin

  1. Create Application Class
  2. Edit the Application Class as Follows

    class FTApplication: MultiDexApplication() {
    override fun attachBaseContext(base: Context?) {
        super.attachBaseContext(base)
        MultiDex.install(this)
    }
    
    init {
        instance = this
    }
    
    val mFTActivityLifecycleCallbacks = FTActivityLifecycleCallbacks()
    
    override fun onCreate() {
        super.onCreate()
    
        registerActivityLifecycleCallbacks(mFTActivityLifecycleCallbacks)
    }
    
    companion object {
        private var instance: FTApplication? = null
    
        fun currentActivity(): Activity? {
    
            return instance!!.mFTActivityLifecycleCallbacks.currentActivity
        }
    }
    
     }
    
  3. Create the ActivityLifecycleCallbacks class

    class FTActivityLifecycleCallbacks: Application.ActivityLifecycleCallbacks {
    
    var currentActivity: Activity? = null
    
    override fun onActivityPaused(activity: Activity?) {
        currentActivity = activity
    }
    
    override fun onActivityResumed(activity: Activity?) {
        currentActivity = activity
    }
    
    override fun onActivityStarted(activity: Activity?) {
        currentActivity = activity
    }
    
    override fun onActivityDestroyed(activity: Activity?) {
    }
    
    override fun onActivitySaveInstanceState(activity: Activity?, outState: Bundle?) {
    }
    
    override fun onActivityStopped(activity: Activity?) {
    }
    
    override fun onActivityCreated(activity: Activity?, savedInstanceState: Bundle?) {
        currentActivity = activity
    }
    
    }
    
  4. you can now use it in any class by calling the following: FTApplication.currentActivity()

2018/12/21

getCurrentActivity() is also in ReactContextBaseJavaModule.
(Since the this question was initially asked, many Android app also has ReactNative component - hybrid app.)

class ReactContext in ReactNative has the whole set of logic to maintain mCurrentActivity which is returned in getCurrentActivity().

Note: I wish getCurrentActivity() is implemented in Android Application class.

2017/12/07