dotnet/wpf · error · InvalidOperationException

SR.DialogResultMustBeSetAfterShowDialog

Error message

SR.DialogResultMustBeSetAfterShowDialog

What it means

The DialogResult property setter throws InvalidOperationException if the window was not shown with ShowDialog. DialogResult only has meaning for modal dialogs; setting it on a non-modal window (shown with Show) is invalid because there is no ShowDialog call to return to.

Solutions

  1. Ensure the window is opened with ShowDialog() when DialogResult is set.
  2. Instead of DialogResult, use Close() and a custom property/event for non-modal windows.
  3. Guard the setter with a check of your own modal flag before assigning DialogResult.

Example fix

// before
resultWindow.Show();
resultWindow.DialogResult = true; // throws
// after
resultWindow.ShowDialog(); // DialogResult now allowed
Defensive patterns

Strategy: validation

Validate before calling

bool canSetDialogResult(Window w, bool shownModally) => shownModally; // track whether window was opened via ShowDialog

Try / catch

try { w.DialogResult = true; }
catch (InvalidOperationException) { w.Close(); }

Prevention

When it happens

Trigger: Setting this.DialogResult = true/false in code-behind of a window that was displayed via Show() instead of ShowDialog().

Common situations: Sharing a window class sometimes opened modally and sometimes not; setting DialogResult in a button handler whose window was activated non-modally; code converted from MessageBox-style flows.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ce9f67b767aa5191. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Window.cs:1382

                    {
                        _dialogResult = value;

                        // if DialogResult is set from within a Closing event then
                        // the window is in the closing state.  Thus, if we call
                        // Close() again from here we go into an infinite loop.
                        //
                        // Note: Windows OS bug # 934500 Setting DialogResult
                        // on the Closing EventHandler of a Dialog causes StackOverFlowException

                        if(!_isClosing)
                        {
                            Close();
                        }
                    }
                }
                else
                {
                    throw new InvalidOperationException(SR.DialogResultMustBeSetAfterShowDialog);
}
            }
        }

        /// <summary>
        ///     The DependencyProperty for WindowStyleProperty.
        ///     Flags:              None
        ///     Default Value:      WindowStyle.SingleBorderWindow
        /// </summary>
        public static readonly DependencyProperty WindowStyleProperty =
                DependencyProperty.Register("WindowStyle", typeof(WindowStyle), typeof(Window),
                        new FrameworkPropertyMetadata(
                                WindowStyle.SingleBorderWindow,
                                new PropertyChangedCallback(_OnWindowStyleChanged),
                                new CoerceValueCallback(CoerceWindowStyle)),
                        new ValidateValueCallback(_ValidateWindowStyleCallback));

        /// <summary>

View on GitHub (pinned to 81131a70a4)