Show MessageBox but continue async execution

Question

In a WinForms project I have an algorithm running that continually computes data and updates the UI. It looks like this:

async Task BackgroundWorkAsync() {
    while (true) {
        var result = await Compute();
        UpdateUI(result);
    }
}

Sometimes, depending on what result contains I want to show a MessageBox but continue running the algorithm immediately. The following does not work because it blocks further processing until the MessageBox is dismissed:

while (true) {
    var result = await Compute();
    UpdateUI(result);
    if (...) MessageBox.Show(...); //new code
}

How can I make the MessageBox.Show call non-blocking?

(Yes, this means that multiple message boxes might pop up at the same time. That's OK.)

It could be annoying for the user but you can create a `Form` and `Show` it to the user. — Reza Aghaei, Dec 19 '15 at 16:15
Can `BackgroundWorkAsync`/`Compute` run on a background thread? — Stephen Cleary, Dec 19 '15 at 16:44
`BackgroundWorkAsync` is started in the Load event and runs on the UI thread. What `Compute` does internally should not matter I think. There might be a UI dependency in it. — boot4life, Dec 19 '15 at 16:46
I recently answered a similar question: http://stackoverflow.com/a/33411037/1768303 — noseratio, Dec 20 '15 at 22:09

score 2 · Answer 1 · answered Dec 19 '15 at 18:38

As soon as the code is running at WinForms UI thread, you can use either Control.BeginInvoke if this code is inside a Form or Control, or the more general SynchronizationContext.Post like this

if (...)
    BeginInvoke(new Action(() => MessageBox.Show(...)));

or

if (...)
    SynchronizationContext.Current.Post(_ => MessageBox.Show(...), null);

score -1 · Answer 2 · edited Oct 13 '21 at 03:38

-1

while (true) {
    var result = await Compute();
    UpdateUI(result);
    if (...) Task.Run(() => { MessageBox.Show(...); });
}

That should suffice if you don't care about which button a user presses in the popup.

edited Oct 13 '21 at 03:38

MarredCheese

13,598
5
77
79

answered Dec 19 '15 at 18:50

Max Yakimets

1,197
7
12

This runs the message box on a separate thread which makes it non-modal and causes multiple message loops. – boot4life Dec 20 '15 at 11:55
He-he, sorry for necroposting, it's been a while since I visited SO... Anyway: you wanted the message box to become non-blocking, wanted to receive multiple of them - you get it. Why then require now for them to be modal and reside within the main message loop? – Max Yakimets Apr 14 '21 at 07:50

Show MessageBox but continue async execution

2 Answers2