ResourceLoader.GetString throws COMException (NamedResource Not Found) for keys containing '.' in WinUI 3 desktop app #6247
Description
Describe the bug
When calling:
var loader = new ResourceLoader();
var value = loader.GetString("XXXXX.Common.Yes");a COMException is thrown:
NamedResource Not Found.
The resource key does exist in Resources.resw.
If the key is changed from:
XXXXX.Common.Yes
to:
XXXXX_Common_Yes
the lookup succeeds immediately.
This indicates that resource keys containing . may not be resolved correctly by ResourceLoader.GetString.
The exception originates from WinRT resource lookup and is reported by Visual Studio at throw time (even if later caught).
API reference:
https://learn.microsoft.com/windows/windows-app-sdk/api/winrt/microsoft.windows.applicationmodel.resources.resourceloader.getstring
https://github.com/microsoft/WindowsAppSDK/blob/main/dev/MRTCore/mrt/Microsoft.Windows.ApplicationModel.Resources/src/ResourceLoader.cpp
Steps to reproduce the bug
Create a new WinUI 3 Desktop project (C#/C++).
Add a string resource in Resources.resw:
Name: XXXXX.Common.Yes
Value: Yes
Call:
var loader = new ResourceLoader();
var value = loader.GetString("XXXXX.Common.Yes");Observe that COMException (NamedResource Not Found) is thrown.
Change the key to:
XXXXX_Common_Yes
Update the code accordingly and rerun.
Observe that the lookup succeeds.
Expected behavior
WinUI 3 (via Windows App SDK)
Desktop application
Note: This behavior was observed in a desktop project. Packaged vs. unpackaged scenarios have not been independently verified, so no conclusion is made regarding packaging impact.
Screenshots
NuGet package version
Windows App SDK 1.8.5: 1.8.260209005
Packaging type
Unpackaged
Windows version
Insider Build (xxxxx)
IDE
No response
Additional context
Replacing . with _ consistently resolves the issue.
This may relate to URI fragment semantics or MRT/PRI key normalization.
Clarification would be appreciated on whether . is officially supported in resource keys for ResourceLoader.GetString.