让MessageBox出现一次（计时器内的代码）

Question

UPDATE: I've managed to fix my problem. Using the code below, I moved my MessageBox AFTER my XML saving and changed the Timer from 100ms to 400ms. I now have 1 box appear, thank god. Although If anyone has a short cut to updating a single value (ActReminded) in the List array(ActListTask), that'd be great to know.

I'm having a little issue with displaying the MessageBox. Show inside a timer without it spamming me. Here's the part of the code I've been working with:

public class ActiveTasks
    {
        //Properties here
    }

public List<ActiveTasks> ActTaskList = new List<ActiveTasks>();

for (int i = 0; i < ListActive.Items.Count; i++)
        {
            if (DTime.Date == newDateTime.Date)
            {
                if (newDateTimeLeft.CompareTo(TimeSpan.Zero) <= 0 && ActTaskList[i].ActReminded != "true")
                {
                    MessageBox.Show("!!!!");
                    ActTaskList.Add(new ActiveTasks()
                    {
                        ActTitle = ActTaskList[i].ActTitle,
                        ActDesc = ActTaskList[i].ActDesc,
                        ActDate = ActTaskList[i].ActDate,
                        ActTime = ActTaskList[i].ActTime,
                        ActStatus = ActTaskList[i].ActStatus,
                        ActReminded = "true",
                        ActRepeat = ActTaskList[i].ActRepeat
                    });

                    ListActive.Items.RemoveAt(i);

                    ActTaskList.RemoveAt(i);

                    XDocument XmlActTasks = GenerateActiveListToXML(ActTaskList);
                }
            }
        }

I actually decided I may want to hold onto the reminder status, whether it has been shown or not as I wouldn't want a repeated reminder every time the program is opened. Since I don't know of a way to update an individual part of ActTaskList I just re-added it, and then deleted the original. This code manages to recognise that if it happens, it will change the reminder status from false, to true; after I've Ok'ed all the spam. So it will stop the MessageBox once I've managed to closed all the Messageboxes. However, it doesn't stop the spam. Would it be anything to do with the fact I've set the timer to 100ms? Or could their be an alternative way to make the messagebox appear without it being inside the timer?

Answer 1

The odds of the current time lining up exactly to the second what is happening in your loop is small. Why not treat newDateTime as a cut off point and just set a flag?

//Declare this outside of the loop
bool hasDisplayed = false;

//Inside the timer event handler
if (!hasDisplayed && DateTime.Now >= newDateTime)
{
    hasDisplayed = true;

    MessageBox.Show("!!!!!!!!!!!!!");
}

Answer 2

Can you do something like this?

Action message = () => MessageBox.Show("!!!!!!!!!!!!!"));
object lockOb = new object();

void timer_Elapsed(object sender, ElapsedEventArgs e)
{
    lock(lockOb)
        if(null != message)
        {
            message();
            message = null;
        }
}

Answer 3

You say you've already tried a boolean indicating the message has already been shown, I'm assuming because the code probably looked like it did below.

void TimerLoop()
{
    bool msgAlreadyShown;

    if(!msgAlreadyShown)
    {
        MessageBox.Show("!!!!!!!");
    }
    // Other work in your timer function
}

The problem with that code is that the bool will be set to false each time the function is called by the timer. You haven't posted much code, but you've at least stated what you're trying to accomplish, a timer that checks if a reminder should be presented to the user.

I'm about to make some wild guesses about how you've put together your software, there's a good chance it's way off, but I hope it might point you in the right direction. You could have some sort of reminder class like this:

public class Reminder
{
    string Message { get; set;}
    DateTime Alarm { get; set; } 
    bool IsDismissed { get; set; }
}

I'm assuming you might want to have multiple reminders that can be checked for in the timer loop, so your timer loop could look something like:

private List<Reminder> _activeReminders; // A list of reminders

void TimerLoop(object s, ElapsedEventArgs e)
{
    lock(_activeReminders) 
    {
        var now = DateTime.Now;
        foreach(var reminder in _activeReminders)
        {
            // only run this code if the time has passed and it hasn't already
            // been shown
            if(now.CompareTo(reminder.Alarm) >= 0 && !reminder.IsDismissed)
            {
                MessageBox.Show(reminder.Message);
                reminder.IsDismissed = true;
            }
        }
    }
}

This is a pretty naive implementation, since you probably don't want to hold onto the reminders for forever and the reminders are never removed from the _activeReminders list, but you essentially just need to add some sort of state to determine if the reminder has already been shown.

Of course, this isn't a complete example either, since I never new up the _activeReminders field or add anything to it, but I think this might help get the idea of what you need to do across. Also, you might not care about multiple reminders, and your timer code could look nothing like this. The main idea was to show you how you can keep track of the state of a reminder, and tailor it to your own code. The above was just an example.

Also, I haven't actually tested it, so treat it more like pseudocode than anything else. However, the logic is sound, and should it should only cause the message box to appear once.