How to get current activity from activity stack in android

See more:

Android

Hello ,I want to get current activity from activity stack , But I don't know how!?

for example:

Activity a = //get activity from activity stack

What I have tried:

I tried this :

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