Call MessageBox from async thread with Form1 as parent

Question

After clicking button1 placed on form1, program is checking if the new version is available (via internet), but doing this in the new thread (not to freeze the form during check).
When the new version is found or not, the appropriate MessageBox is shown, but it has no parent (because it was called from the thread, not directly from the form1).

How to make the MessageBox display with form1 as a parent?

score 51 · Accepted Answer · edited Jul 31 '12 at 14:32

51

this.Invoke(new Action(() => { MessageBox.Show(this, "text"); }));

This will switch to main thread and show MessageBox with form1 parent.

edited Jul 31 '12 at 14:32

Otiel

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answered Mar 18 '11 at 08:22

Stecya

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This gives me a lot of compilation errors (ie. Error 1 Keyword 'this' is not valid in a static property, static method, or static field initializer) – Dawid Moś Mar 18 '11 at 08:29
Instead `this` use instance of your form1 – Stecya Mar 18 '11 at 08:32
How do you get the DialogResult here though? Invoke returns an object, and it is null. – Stealth Rabbi Dec 16 '13 at 16:04
@StealthRabbi: See my answer for that particular scenario. – Derek W Apr 14 '14 at 21:01

score 14 · Answer 2 · answered Apr 14 '14 at 21:00

While the selected answer provides a nice way of displaying the MessageBox from an asynchronous thread, it doesn't handle the case where you want to retrieve the DialogResult from that particular MessageBox being shown.

If you are looking to return a DialogResult from the invoked MessageBox displayed on top of the Form. Then you need to use the Func delegate instead of the Action delegate.

Action delegates always return void while Func has a return value.

Here is a little method that I devised to handle this particular scenario:

private DialogResult BackgroundThreadMessageBox(IWin32Window owner, string text)
{
   if (this.InvokeRequired)
   {
      return (DialogResult) this.Invoke(new Func<DialogResult>(
                             () => { return MessageBox.Show(owner, text); }));
   }
   else
   {
      return MessageBox.Show(owner, text);
   }
}

Although this isn't typically considered best practice or design it will work in a pinch.

Just out of curiosity, what would a better practice/design be? — Eric Pohl, Mar 07 '17 at 15:11

score 5 · Answer 3 · answered Mar 18 '11 at 08:23

5

  if ( Form1.InvokeRequired ) {
            Form1.Invoke((Action)delegate{MessageBox.Show(Form1,"Hello");});
        }

answered Mar 18 '11 at 08:23

Arsen Mkrtchyan

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In THIS case, since `MessageBox` is always called from another thread, using `if ( Form1.InvokeRequired )` is useless here. – Yousha Aleayoub May 16 '20 at 19:15
if it is always, than agree – Arsen Mkrtchyan May 18 '20 at 07:02

score 0 · Answer 4 · answered Jun 01 '16 at 20:24

0

In my case, I was in another class and had a reference for a textbox, so I used the code below:

_txtResultado.Dispatcher.Invoke(DispatcherPriority.Normal, new Action(delegate ()
{
    MessageBox.Show("My message!");
}));

answered Jun 01 '16 at 20:24

Ricardo França

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score 0 · Answer 5 · answered Mar 18 '11 at 08:23

Try using a backgroundworker.

private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
   //Helper thread: Long during task
}

private void backgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    //We're in the main thread: Show your messagebox
}

Call MessageBox from async thread with Form1 as parent

5 Answers5

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