dotnet/wpf · error · InvalidOperationException

SR.ShowDialogOnVisible

Error message

SR.ShowDialogOnVisible

What it means

Window.ShowDialog shows a window modally and requires the window not already be visible. If ShowDialog is called while the window is already shown (_isVisible), WPF throws InvalidOperationException(SR.ShowDialogOnVisible). A window cannot become modal twice.

Solutions

  1. Check window.IsVisible before calling ShowDialog and skip/queue the call if already visible
  2. Create a new Window instance for each modal session instead of reusing one
  3. Disable the invoking button while the dialog is open
  4. Track dialog state and return the existing DialogResult rather than re-showing

Example fix

// before
private void OpenSettings() {
    _settingsWindow.ShowDialog(); // throws if already visible
}
// after
private void OpenSettings() {
    if (_settingsWindow == null || !_settingsWindow.IsVisible) {
        _settingsWindow = new SettingsWindow();
        _settingsWindow.ShowDialog();
    }
}
Defensive patterns

Strategy: validation

Validate before calling

if (!window.IsVisible) { window.ShowDialog(); }

Type guard

bool CanShowDialog(Window w) => !w.IsVisible && !w.IsLoaded || !w.IsVisible;

Try / catch

try { window.ShowDialog(); } catch (InvalidOperationException ex) when (ex.Message == SR.ShowDialogOnVisible) { window.Activate(); }

Prevention

When it happens

Trigger: Calling ShowDialog() on a Window instance whose Show() or ShowDialog() has already been called and which has not closed; re-invoking ShowDialog from a button handler after the dialog is already displayed.

Common situations: Double-click on a UI button firing ShowDialog twice; calling ShowDialog in a loop or re-entrantly from dialog events; reusing a cached window instance that is still open instead of creating a new one.

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/45b269f16855e6b6. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Window.cs:280

        ///     Shows the window as a modal window
        /// </summary>
        /// <returns>bool?</returns>
        /// <remarks>
        ///     Callers must have UIPermission(UIPermissionWindow.AllWindows) to call this API.
        /// </remarks>
        public Nullable<bool> ShowDialog()
        {
            // this call ends up throwing an exception if ShowDialog
            // is not allowed
            VerifyApiSupported();
            VerifyContextAndObjectState();
            VerifyCanShow();
            VerifyNotClosing();
            VerifyConsistencyWithAllowsTransparency();

            if (_isVisible)
            {
                throw new InvalidOperationException(SR.ShowDialogOnVisible);
            }
            else if (_showingAsDialog)
            {
                throw new InvalidOperationException(SR.ShowDialogOnModal);
            }

            _dialogOwnerHandle = _ownerHandle;

            // verify owner handle is window
            if (!UnsafeNativeMethods.IsWindow( new HandleRef( null, _dialogOwnerHandle ) ))
            {
                _dialogOwnerHandle = IntPtr.Zero;
            }


            // remember the current active window;
            // this is used when dialog creation fails or dialog closes, we set the active window back to this one.
            _dialogPreviousActiveHandle = UnsafeNativeMethods.GetActiveWindow();

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