Home/ Questions/Q 4042288
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-20T12:59:12+00:00

Surprisingly one can show more than one dialog at a time by putting the

  • 0

Surprisingly one can show more than one dialog at a time by putting the ShowDialog() call on the Dispatcher:

uiDispatcher.BeginInvoke(new Func<bool?>(myWindow.ShowDialog));

How come this works and still the UI remains running responding to user interaction once the dialog is shown (I would have thought not since ShowDialog() blocks the thread it is on which has to be the UI thread), one can even go on showing new dialogs:

Window myWindow;
for(int i = 0; i < 5; i ++)
{
  myWindow = new Window(); 
  uiDispatcher.BeginInvoke(new Func<bool?>(myWindow.ShowDialog));
}

And the UI is still responsive.

Is there something I should beware of relying on this behaviour? (I want to show one dialog on top of another when some background thread wants to – this works – the only unwanted behaviour seems to be when switching apps sometimes WPF does not know which dialog should be on top – but still allows you to bring one of the dialogs to the front by clicking on it which is unusual for a dialog as clicking outside a dialog is usually not allowed).

UPDATE: One issue I have come across is if you hide one of your dialogs the user can interact with all other Windows again! (not just the other dialogs). See: WPF Dialog not modal?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Showing a dialog does not block the UI thread — otherwise you won’t be able to interact with the dialog.

    It merely marks the fact that there is a modal dialog outstanding, and that it should disable inputs to all other non-dialog windows.

    If you shuff a ShowDialog call into the dispatcher, the dispatcher will allow an additional dialog to be created because you are not doing something which is prohibited when a modal dialog is outstanding — which is to input into other non-dialog windows.

    Your new dialog is fully functional, because it is a dialog, and you are not trying to input into non-dialog windows.

    Switching applications should bring any modal dialog out to the front, but since you have more than one modal dialogs, the system will get confused as to which one should be top-most. I’d suggest you trap the activation event and just manually bring the necessary dialog top-most.

    • 0