ShowDialog() from within a ShowDialog() – both closing

I hit this really weird behavior with Win Forms dialog boxes just now.

Try opening a Dialog Box inside another DialogBox in .NET (1.1 or 2.0) and setting the DialogResult on the second form to be one of the results (OK, Cancel etc). The second dialog box will close, but the first dialog box will also close.

For example, say you have a dialog with two buttons. Button1 opens a new instance of the dialog, and Button2 closes its parent form (the form on which it exists) by setting DialogResult to be DialogResult.OK:

class MyDialog : Form
   private void Button1_Click(object sender, EventArgs e)
      new MyDialog().ShowDialog(this);

   private void Button2_Click(object sender, EventArgs e)
      DialogResult = DialogResult.OK;

If the user clicks Button1 multiple times and then hits Button2 just once, all the dialog boxes will be closed one after another.

To solve this problem, you need to reset the DialogResult to None after you call a dialog box from another dialog box:

   private void Button1_Click(object sender, EventArgs e)
      new MyDialog().ShowDialog(this);
      DialogResult = DialogResult.None;


Not sure for the reason behind this behavior, but there it is... I was stumped there for a few minutes.

Edit: BTW - this only reproes if you set the AcceptButton and CancelButton properties on the form to point to the buttons you created. Apparently that's the trigger that manifests the bug.

Comments (10)

  1. Gabe says:

    This isn’t too hard to explain. The only way your Button2_Click() function could have the result of closing the dialog box is if there is some magic in the form code which checks after the event to see if the DialogResult has changed, and to close the dialog and return if it has.

    Of course you were probly expecting that ShowDialog() would not modify its owner’s DialogResult, but if it did then Button1_Click() wouldn’t work because you never assign its return value to anything.

    Why does ShowDialog() modify its owner’s state? Probably to make it easier to get the same behavior as VB6 or something like that.

  2. Shahar Prish says:



    Not sure I follow.

    I am not doing anything with the DialogResult in Button1 – that’s intentional. Even if I did assign it to a local variable and read it, the behavior would be identical.

    The only problem here, that I can see, is that the value somehow gets propagated to the parent, like you say. This behavior was not in VB6, VB5, VB4, Access 2.0, Access 95, MFC or even WTL (from what little I used WTL).

    I dont think this is a backward compatibility issue.

  3. I’m glad someone else has hit this bug too!

    How about we get this one, and the one where if you have a dialog open and you show another dialog and then close that dialog the next available application in the task manager will get the focus? It’s not like it hasn’t been around for long enough, it’s been there since VB3 and probably earlier….

  4. Jens K says:

    > I was stumped there for a few minutes.

    Just a few minutes? 😉

    Thanks for that hint.

    In this case I definitelay dodn’t understand thsi behavior…

  5. Hi Shahar

    Thanks a lot for this tip, I was really quite stumped.



  6. Bill Brekke says:

    Thanks! Yes, this code works  as described above to prevent the second underlying form from closing in a string of showdialogs when placed after the calling showdialog.  Thanks.

         DialogResult = DialogResult.None;

    This string is just so other people can google this solution easier: " Showdialog closes form when it should not "

  7. Maxxxx says:

    This still hasn't been fixed in .NET 4. Wasted almost a day to figure it out 🙁

  8. dani says:


    InnerDialog inner = new InnerDialog()

       DialogResult innerResult = inner.ShowDialog(this);

       this.DialogResult = DialogResult.None;

  9. Tom Bushell says:

    I got bitten by this because I had copy/pasted some buttons from another form, not realizing that one of the **buttons** had it's DialogResult property set to **DialogResult.Cancel**.

    When clicked, this was setting the containing form's DialogResult, causing it to close.

    Resetting it to **DialogResult.None** fixed the problem.

    So, check the DialogResult properties on all your modal dialogs.

  10. Vitor Castanheiro says:

    Thanks! Thanks! Thanks a million!

    I was struggling with that! that's the key. DialogResult is assigned to the ShowDialog Function of the form. Worked for me to set it to none!

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