Can't set DialogResult in WPF

Question

I show a WPF window using ShowDialog() from the calling window. The window opens and is modal as expected. However, in my OK and Cancel button's click events in the dialog window I set this.DialogResult = true (or false) respectively, and the value does not get set. The window closes as expected, but DialogResult is still null.

Is this a bug in WPF? Or is there a reason the DialogResult property cannot be set yet does not throw an exception? The window is not hosted in a browser.

Code in the calling window:

Window2 win = new Window2();
bool? result = win.ShowDialog();
if (result.HasValue && result.Value) {
   //never gets here because result is always null
}

Code in the dialog window:

this.DialogResult = true;

Answer 1

Is the window hosted in a browser? If so, you can't set that property for this window.

Answer 2

Well first of all you have to take into account that it returns a nullable bool (bool?), so in order to compare it or set it to another variable you have to cast it to a regular bool

bool result = (bool)myWindow.DialogResult;

As for it being null... I don't see why that should happen, unless it's somehow being set back to null AFTER being set to true or false. Can you show your code?

EDIT:

Your code worked fine for me, this is what I have in the second window:

private void button2_Click(object sender, RoutedEventArgs e)
{
    this.DialogResult = false;
}

private void button1_Click(object sender, RoutedEventArgs e)
{
    this.DialogResult = true;
}

And in Window1:

private void window1_Loaded(object sender, RoutedEventArgs e)
{
    Window2 win = new Window2();

    bool? result = win.ShowDialog();

    if (result.HasValue && result.Value)
    {
     //it DID get here
    }
}

Is there any big difference?

Answer 3

DialogResult is a nullable bool. However you do not have to cast it to get it's value.

bool? result = myWindow.ShowDialog();
if (result ?? false)
{
  // snip
}

The ?? sets the default value to return if the result is null. More information: Using Nullable Types (C# Programming Guide)

As for the original issue, the only time I have seen this is when the window is being disposed between you setting the DialogResult/closing the window and you testing the dialog result. There is not much I can do to help except point you in this direction and tell you to debug it.

HTH,

Answer 4

Do you close the window before u set the DialogResult? You should post the whole content of your button event-handlers.