android 获得当前活动的Acticity
ActivityManager activityManager = (ActivityManager) getSystemService(ACTIVITY_SERVICE);
ComponentName componentName = activityManager.getRunningTasks(1).get(0).topActivity;
Log.d("", "package:"+componentName .getPackageName());
Log.d("", "class:"+componentName .getClassName());
添加权限：android.permission.GET_TASKS
