Ignore notifications as the current foreground package in AppLock service

Question

I am creating an AppLock and it is working perfectly. I have a service which checks for the current foreground apps using UserStat. I am currently showing and hiding app lock on the basis of package change. But whenever any notification comes, it takes the position of current foreground app and my app lock hides. Due to change in package name.

Here's my code for getting the current foreground package.

@TargetApi(Build.VERSION_CODES.LOLLIPOP)
public static String getCurrentAppPackage(Context context) {
    String topPackageName = null;
    UsageStatsManager usage = (UsageStatsManager) context.getSystemService(Context.USAGE_STATS_SERVICE);
    long time = System.currentTimeMillis();
    List<UsageStats> stats = usage.queryUsageStats(UsageStatsManager.INTERVAL_DAILY, time - 1000 * 1000, time);
    if (stats != null && stats.size() > 0) {
        SortedMap<Long, UsageStats> runningTask = new TreeMap<>();
        for (UsageStats usageStats : stats) {
            runningTask.put(usageStats.getLastTimeUsed(), usageStats);
        }
        if (runningTask.isEmpty()) {
            return null;
        }
        topPackageName = runningTask.get(runningTask.lastKey()).getPackageName();
    }
    if (topPackageName == null) {
        Intent intent = new Intent(Settings.ACTION_USAGE_ACCESS_SETTINGS);
        context.startActivity(intent);
    }
    return topPackageName;
}