HeadsUp通知未显示在KitKat上

我有一条通知，使用以下代码显示:

I have a notification, presented using the following code:

    // Create the notification
    android.app.Notification systemNotification = new NotificationCompat.Builder(context)
            // Set notification data and appearance
            .setContentTitle(notification.getNotificationLabel())
            .setContentText(notification.getMessage())
            .setSmallIcon(notification.getNotificationDrawable())
            .setWhen(new Date().getTime())

            // Set notification options
            .setCategory(NotificationCompat.CATEGORY_MESSAGE)
            .setPriority(NotificationCompat.PRIORITY_HIGH)
            .setDefaults(NotificationCompat.DEFAULT_ALL)
            .build()
    ;

    NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);

    notificationManager.notify(notification.getNotificationId(), systemNotification);

在Lollypop及更高版本上运行时，它可以正常工作，并且该通知会同时显示在状态栏中和预期/期望的弹出通知中.在奇巧(Kitkat)上，通知仅显示在状态栏中，没有弹出通知.我仍然可以从状态栏打开通知，一切看起来和工作都很好，只是缺少了弹出通知.

When run on Lollypop and newer, it works fine and the notification appears both in the status bar and as a popup notification as expected/desired. On Kitkat, the notification only appears in the status bar, there's no popup notification. I can still open the notification from the status bar and everything looks and works fine, it's just the popup notification that's missing.

到目前为止我已经尝试过的一些事情:

Some of the things I've tried so far:

• setDefaults
的不同选项
• setPriority
的不同选项
• 已验证该应用程序的系统设置面板中的通知已打开

• different options to setDefaults
• different options to setPriority
• verified that notifications are on in the system settings panel for the application