FileSavePicker FileTypeChoices incorrect

[trungnt2910]

Current behavior

I have this code:

            var savePicker = new Windows.Storage.Pickers.FileSavePicker();
            savePicker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.DocumentsLibrary;
            savePicker.FileTypeChoices.Add("C/C++ source files", new List<string>() { ".cpp", ".c", ".cc", ".cxx", ".c++", ".cp" });
            savePicker.SuggestedFileName = "Hacked";
            Windows.Storage.StorageFile file = await savePicker.PickSaveFileAsync();

However, instead of showing these file types, they show .cp, .com, .exe, .bin.

Expected behavior

It shows the right file types, like in the my UWP-only project:

How to reproduce it (as minimally and precisely as possible)

• Create a Uno project.
• Open a FileSavePicker, like in the code above.
• Build the WASM project.

Workaround

Found none.

Environment

Nuget Package:

• Uno.UI / Uno.UI.WebAssembly / Uno.UI.Skia
• Uno.WinUI / Uno.WinUI.WebAssembly / Uno.WinUI.Skia
• Uno.SourceGenerationTasks
• Uno.UI.RemoteControl / Uno.WinUI.RemoteControl
• Other:

Nuget Package Version(s):

Affected platform(s):

• iOS
• Android
• WebAssembly
• WebAssembly renderers for Xamarin.Forms
• macOS
• Skia
  • WPF
  • GTK (Linux)
  • Tizen
• Windows
• Build tasks
• Solution Templates

IDE:

• Visual Studio 2017 (version: )
• Visual Studio 2019 (version: 16.9.3)
• Visual Studio for Mac (version: )
• Rider Windows (version: )
• Rider macOS (version: )
• Visual Studio Code (version: )

Relevant plugins:

• Resharper (version: )

Anything else we need to know?

FileOpenPicker seems to work well. Only FileSavePicker fails.

[jeromelaban]

/cc @MartinZikmund

[trungnt2910]

This seems to be the browser's bug. Calling showSaveFilePicker always make Edge add some unrelated file types.

In your implementation, .cpp files map to the default application/octet-stream, which somehow includes .com, .exe, .bin

A workaround is to associate all files with application/x-nonsense-file-type-that-will-never-exist.

[trungnt2910]

uno/src/Uno.UWP/Storage/Pickers/FileSavePicker.wasm.cs

Lines 72 to 84 in 557cd75

	var acceptItems = new List<NativeFilePickerAcceptTypeItem>();
	foreach (var extension in choice.Value)
	{
	var acceptItem = new NativeFilePickerAcceptTypeItem()
	{
	MimeType = MimeTypeService.GetFromExtension(extension),
	Extensions = new[] { extension }
	};
	acceptItems.Add(acceptItem);
	}
	acceptType.Accept = acceptItems.ToArray();
	acceptTypes.Add(acceptType);

Is this expected behavior? This creates a something like this:

[{"accept":[{"extensions":[".cpp"],"mimeType":"application\/octet-stream"},{"extensions":[".c"],"mimeType":"application\/octet-stream"},{"extensions":[".cc"],"mimeType":"application\/octet-stream"},{"extensions":[".cxx"],"mimeType":"application\/octet-stream"},{"extensions":[".c++"],"mimeType":"application\/octet-stream"},{"extensions":[".cp"],"mimeType":"application\/octet-stream"}],"description":"C\/C++ source files"}]

The JS browser code seems to process the "accept" part as a dictionary, meaning that all options, except the last, that has the same mime type will be discarded. That's why only .cp is visible in my browser.

After that, they will append the default, but unrelated .com, .exe, and .bin types.