MahApps/MahApps.Metro · error · MahAppsException

Failed to set the window state for {window} from the setting

Error message

Failed to set the window state for {window} from the settings.

What it means

WindowsSettingBehavior restores a previously saved window placement by calling WinApiHelper.SetWindowPlacement. If that native call throws (e.g. because the persisted RECT is invalid or came from a now-absent monitor), the behavior wraps the exception in a MahAppsException naming the window, preserving the original via InnerException. This protects app startup from a corrupt window-state setting.

Source

Thrown at src/MahApps.Metro/Behaviors/WindowsSettingBehavior.cs:146

            {
                Trace.TraceError($"{this}: The settings for {window} could not be reloaded! {e}");
                return;
            }

            // check for existing placement and prevent empty bounds
            if (settings.Placement is null || settings.Placement.normalPosition.IsEmpty)
            {
                return;
            }

            try
            {
                var wp = settings.Placement.ToWINDOWPLACEMENT();
                WinApiHelper.SetWindowPlacement(window, wp);
            }
            catch (Exception ex)
            {
                throw new MahAppsException($"Failed to set the window state for {window} from the settings.", ex);
            }
        }

        private void SaveWindowState()
        {
            var window = this.AssociatedObject;
            if (window is null)
            {
                return;
            }

            var settings = window.GetWindowPlacementSettings();
            if (settings is null || !window.SaveWindowPosition)
            {
                return;
            }

            var windowHandle = new WindowInteropHelper(window).EnsureHandle();

View on GitHub (pinned to 72099e310b)

Solutions

1. Clear/reset the persisted window placement for the affected window (delete the user setting or set Placement to null) so the window opens with defaults.
2. Catch the MahAppsException at the app level and fall back to default bounds (CenterScreen) instead of crashing.
3. Update to a MahApps version that validates the saved RECT before calling SetWindowPlacement, or sanitize the normalPosition before restoring.
4. Reset the application settings (e.g. delete the user.config file) to discard the corrupt placement.

Example fix

// before: behavior throws, app crashes on startup
// after: guard in your window/settings code — clear bad placement before apply
var settings = window.GetWindowPlacementSettings();
if (settings.Placement is { } p && !IsPlacementValid(p.normalPosition))
{
    settings.Placement = null; // discard corrupt placement
}

// Sanitize the saved placement before letting the behavior apply it
var settings = window.GetWindowPlacementSettings();
if (settings.Placement is { } p) {
    var rect = p.normalPosition;
    bool onScreen = SystemParameters.VirtualScreenLeft <= rect.Left
                    && rect.Right <= SystemParameters.VirtualScreenLeft + SystemParameters.VirtualScreenWidth
                    && (rect.Right - rect.Left) > 0;
    if (!onScreen) settings.Placement = null; // discard, use defaults
}

try {
    // open the window / let the behavior apply placement
} catch (MahAppsException ex) when (ex.Message.Contains("Failed to set the window state")) {
    // reset persisted placement and reopen with defaults
    window.GetWindowPlacementSettings().Placement = null;
    Log.Warn("Discarded invalid window placement", ex.InnerException);
}

When it happens

Trigger: On window load, settings.Placement is non-empty so the behavior calls SetWindowPlacement(window, wp) and the underlying Win32 placement call throws — typically because the saved normalPosition is off-screen, degenerate, or incompatible with the current monitor topology.

Common situations: User previously closed the app on a monitor that is now disconnected (laptop dock change). RDP session with different resolution. Corrupted user settings file. DPI/position values that produce an invalid WINDOWPLACEMENT.

Related errors

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• Could not locate any instances of contract {typeof(T)}.
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AI-assisted analysis of MahApps/MahApps.Metro@72099e310b (2026-08-13). Data as JSON: /api/errors/a268b2ef931c1b4c. Report an issue: GitHub.