No Window.FlowDirection support for desktop applications

WinUI XAML does not support FlowDirection or equivalent attribute on the Window element. Additionally, the Window class does not contain a FlowDirection property for programmatic access.

This impacts developers migrating from WPF XAML or WinRT XAML and overall global readiness.

Potential workaround:

// ...
var native_window = managed_window.As<IWindowNative>();
var extended_style = GetWindowLong(native_window.WindowHandle, GWL_EXSTYLE);
SetWindowLong(native_window.WindowHandle, GWL_EXSTYLE, extended_style | WS_EX_LAYOUTRTL);
managed_window.Activate();
// ...

Steps to reproduce the bug

1. File > New > WinUI 3 blank desktop packaged application
2. Attempt to add FlowDirection=FlowDirection.RightToLeft attribute to root Window element in MainWindow.xaml
3. Observe error

Expected behavior Easy way to enable RTL support via XAML and programmatically.

Version Info NuGet package version: Microsoft.WinUI 3.0.0-preview4.210210.4

Windows app type:

UWP	Win32
	Yes

Windows 10 version	Saw the problem?
Insider Build (21313)	Yes
October 2020 Update (19042)
May 2020 Update (19041)
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

[marb2000]

@riverar, you are right this is basic funtionality that should be there, but it requires a new APIs, and new APIs is a feature request.

[ahass]

any news on this item?