FileSavePicker: Cannot set default extension when defining FileTypeChoices

[d2phap]

Describe the bug

The default extension is always the first item in FileTypeChoices. Also, FileTypeChoices is always sorted, ignoring the original order!

var saveDialog = new FileSavePicker(AppWindow.Id)
{
    DefaultFileExtension = ".xml",
};

saveDialog.FileTypeChoices.TryAdd("TXT", [".txt"]);
saveDialog.FileTypeChoices.TryAdd("JSON", [".json"]);
saveDialog.FileTypeChoices.TryAdd("XML", [".xml"]);

var picker = await saveDialog.PickSaveFileAsync();

Steps to reproduce the bug

Can reproduce with WinUI 3 Gallery:

Expected behavior

The selected extension of "Save as File" dropdown must match in this order:

1. The extension from SuggestedFileName, if it's defined in the FileTypeChoices
2. The DefaultFileExtension if it's defined in the FileTypeChoices.

See MS Paint:

Screenshots

NuGet package version

Windows App SDK 1.8.2: 1.8.251003001

Packaging type

Unpackaged

Windows version

Windows 11 version 24H2 LTSC (26100, June Update)

IDE

Other, Visual Studio 2022

Additional context

No response

[ghost1372]

Fixed in
#5948

[d2phap]

Fixed in #5948

Correct me if I'm wrong. I think the PR only fixes the order of FileTypeChoices, not the default extension DefaultFileExtension which is different issue

[ghost1372]

@d2phap sorry i dont know enough, ask from PR creator