获得当前正在显示的activity的类名

<uses-permission android:name="android.permission.GET_TASKS"/> 

ActivityManager manager = (ActivityManager)   getSystemService(Context.ACTIVITY_SERVICE);    
List<RunningTaskInfo> runningTasks = manager .getRunningTasks(1);    
RunningTaskInfo cinfo = runningTasks.get(0);    
ComponentName component = cinfo.topActivity;    
Log.e("current activity is ", component.getClassName());