dotnet/wpf · error · InvalidOperationException

SR.CantSetOwnerAfterDialogIsShown

Error message

SR.CantSetOwnerAfterDialogIsShown

What it means

Window.Owner setter throws InvalidOperationException if the window is currently being shown modally via ShowDialog. The owner of a modal dialog cannot be changed while the dialog is displayed because WPF has already established the Win32 owner relationship and modal state. You must set the owner before calling ShowDialog.

Solutions

  1. Set the Owner property before calling ShowDialog.
  2. If ownership must change at runtime, close the dialog, change Owner, then ShowDialog again.
  3. Use WindowStartupLocation and owner setup in the parent right after constructing the dialog.

Example fix

// before
var dlg = new OptionsDialog();
dlg.ShowDialog();
dlg.Owner = mainWindow;
// after
var dlg = new OptionsDialog { Owner = mainWindow };
dlg.ShowDialog();
Defensive patterns

Strategy: validation

Validate before calling

bool canSetOwner(Window w) => w != null && !w.IsLoaded; // set owner before window is loaded/shown modally

Try / catch

try { dlg.Owner = owner; dlg.ShowDialog(); }
catch (InvalidOperationException) { dlg.ShowDialog(); }

Prevention

When it happens

Trigger: Setting window.Owner (or Owner property) while _showingAsDialog is true, i.e. after ShowDialog() has been called on the window and before it closes.

Common situations: Assigning an owner from inside the dialog itself (e.g. in Loaded or a button handler), or a parent window trying to re-parent its modal dialog after launch.

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/d20a72dffc1680bc. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Window.cs:1233

                // is not allowed
                VerifyApiSupported();
                VerifyContextAndObjectState();
                return _ownerWindow;
            }
            set
            {
                // this call ends up throwing an exception if accessing Owner
                // is not allowed
                VerifyApiSupported();
                VerifyContextAndObjectState();
                if (value == this)
                {
                    throw new ArgumentException(SR.CannotSetOwnerToItself);
                }

                if (_showingAsDialog)
                {
                    throw new InvalidOperationException(SR.CantSetOwnerAfterDialogIsShown);
                }

                if (value != null && value.IsSourceWindowNull)
                {
                    // Try to be specific in the error message.
                    if (value._disposed)
                    {
                        throw new InvalidOperationException(SR.CantSetOwnerToClosedWindow);
                    }
                    throw new InvalidOperationException(SR.CantSetOwnerWhosHwndIsNotCreated);
                }

                if ( _ownerWindow == value )
                {
                    return;
                }

                if (!_disposed)

View on GitHub (pinned to 81131a70a4)