stride3d/stride · error · InvalidOperationException

Unable to retrieve the HwndSource of this window

Error message

Unable to retrieve the HwndSource of this window

What it means

DragWindow.InitializeExtendedStyle needs the Win32 HwndSource of the WPF Window to apply WS_EX_TRANSPARENT/WS_EX_LAYERED/WS_EX_TOPMOST styles. PresentationSource.FromVisual(this) returns null when the window has no presentation source yet (not fully shown/loaded into a HWND), so an InvalidOperationException is thrown.

Solutions

Hook InitializeExtendedStyle to the SourceInitialized event instead of Loaded/constructor
Guard with a null check on PresentationSource.FromVisual and defer/retry once the window is shown
Ensure Show()/ShowDialog() is actually called and the window is not being manipulated after Close()

Example fix

// before
public DragWindow() { InitializeExtendedStyle(null, null); }
// after
public DragWindow() { SourceInitialized += InitializeExtendedStyle; }

Defensive patterns

Strategy: validation

Validate before calling

var source = PresentationSource.FromVisual(dragWindow);
if (source is HwndSource hwndSource) InitializeStyle(hwndSource.Handle); else dragWindow.SourceInitialized += (s,e) => InitializeExtendedStyle(s, e);

Type guard

static bool TryGetHwndSource(Visual v, out HwndSource src) => (src = PresentationSource.FromVisual(v) as HwndSource) != null;

Try / catch

try { InitializeExtendedStyle(sender, e); }
catch (InvalidOperationException) { window.SourceInitialized += InitializeExtendedStyle; } // defer until HWND exists

Prevention

Always apply Win32 window styles from the SourceInitialized event, not the constructor
Never manipulate HWND-based state after Window.Close()
Guard PresentationSource.FromVisual results for null

When it happens

Trigger: Calling InitializeExtendedStyle (e.g. from a SourceInitialized/Loaded handler wired too early, or constructor) before the window's HWND exists, or after the window was closed.

Common situations: Subscribing the handler in the Window constructor instead of waiting for SourceInitialized; showing the window in a non-WPF-hosted context where no HwndSource is created; calling on a Window that never got shown.

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 stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/178680855cd5a6e7. Report an issue: GitHub.

Appendix: source

Thrown at sources/editor/Stride.Core.Assets.Editor/View/Behaviors/DragDrop/DragWindow.cs:31

        {
            AllowDrop = false;
            AllowsTransparency = true;
            Background = null;
            IsHitTestVisible = false;
            ShowActivated = false;
            ShowInTaskbar = false;
            SizeToContent = SizeToContent.WidthAndHeight;
            Style = null;
            Topmost = true;
            WindowStyle = WindowStyle.None;
            SourceInitialized += InitializeExtendedStyle;
        }

        private void InitializeExtendedStyle(object sender, EventArgs eventArgs)
        {
            var source = (HwndSource)PresentationSource.FromVisual(this);
            if (source == null)
                throw new InvalidOperationException("Unable to retrieve the HwndSource of this window");

            int extendedStyle = NativeHelper.GetWindowLong(source.Handle, NativeHelper.GWL_EXSTYLE);
            extendedStyle = (int)(extendedStyle | NativeHelper.WS_EX_TRANSPARENT | NativeHelper.WS_EX_LAYERED | NativeHelper.WS_EX_TOPMOST);
            NativeHelper.SetWindowLong(source.Handle, NativeHelper.GWL_EXSTYLE, extendedStyle);
        }
    }
}

View on GitHub (pinned to 96fad776d2)