How to push a message loop in WinForms?

Question

In WPF, I can push a message loop using Dispatcher.PushFrame.

What is the equivalent in WinForms? I'm familiar with DoEvents but that must be called in a loop which can spin the CPU instead of the very efficient approach of just waiting for a message or for an event to signal to exit (like Dispatcher.PushFrame has).

There isn't one, ShowDialog() is as close as it gets. I poked at alternatives for a while but the re-entrancy caused too many problems. — Hans Passant, Feb 01 '16 at 10:26
I've settled on `DoEvents` within a loop with a Sleep to keep the CPU from spinning to high. — Andrew Arnott, Feb 06 '16 at 15:37

score 1 · Answer 1 · answered Sep 07 '19 at 19:26

I was able to include WindowsBase to my project's references and just use Dispatcher.PushFrame and frame.Continue = false as usual.

Any caveats with wpf-winforms interop apply, and it does require part of wpf to be referenced, but it should still be better than DoEvents (which has severe pitfalls).

score -1 · Answer 2 · answered Feb 01 '16 at 06:56

-1

This is the equivalent:

        System.Threading.SendOrPostCallback callback = o =>
        {
            this.Text = "Hello" + o.ToString(); // "Hello42"
        };
        WindowsFormsSynchronizationContext.Current.Post(callback, 42);

The 42 is a state parameter that gets past to the callback.

You can also do this:

        this.BeginInvoke((Action)(() => this.Text = "Hello"));

BTW, you should never ever ever use DoEvents - it's a great way to introduce bugs in to your code and is really only there for VB6 compatibility.

answered Feb 01 '16 at 06:56

Enigmativity

113,464
11
89
172

No, that's not the equivalent. That's just posting a message. My question is how to push a message loop that would process such a message. I agree on `DoEvents` being exceptionally problematic and I avoid it like the plague. Nevertheless, for this unit test I'm writing, I don't need to worry about stray messages being processed and I do need to simulate the UI thread processing events since there in fact is *no* main message loop in my unit test. – Andrew Arnott Feb 06 '16 at 15:36

How to push a message loop in WinForms?

2 Answers2