SaveFileDialog does not append file extension to file name

Describe the bug When saving a file with FilePickerSaveOptions or SaveFileDialog, the dialog doesn’t append the file extension to the user’s selected file name.

To Reproduce

var saveFileDialog = new SaveFileDialog
{
	Title = "Where to export Library",
	Filters = new()
	{
		new() { Name = "Excel Workbook (*.xlsx)", Extensions = new() { "xlsx" } }
	}
};

var fileName = await saveFileDialog.ShowAsync(this);
//fileName has no file extension

Expected behavior After the FilePickerSaveOptions and SaveFileDialog close, the user-selected file name should have the file extension of selected FileTypeChoices.

Desktop (please complete the following information):

• OS: Windows
• Version 11.0.0-preview4

[Mbucari]

The problem was with my patterns. I should have used the GLOB patterns like so:

new("Excel Workbook (*.xlsx)") { Patterns = new[] { "*.xlsx" } },
new("CSV files (*.csv)") { Patterns = new[] { "*.csv" } },
new("JSON files (*.json)") { Patterns = new[] { "*.json" } },
new("All files (*.*)") { Patterns = new[] { "*" } }

[Mbucari]

Here’s an example using StorageProvider.

var options = new FilePickerSaveOptions
{
	Title = "Where to export Library",
	SuggestedStartLocation =  new Avalonia.Platform.Storage.FileIO.BclStorageFolder(Configuration.Instance.Books),
	ShowOverwritePrompt = true,
	FileTypeChoices = new FilePickerFileType[]
	{
		new("Excel Workbook (*.xlsx)") { Patterns = new[] { "xlsx" } },
		new("CSV files (*.csv)") { Patterns = new[] { "csv" } },
		new("JSON files (*.json)") { Patterns = new[] { "json" } },
		new("All files (*.*)") { Patterns = new[] { "*" } },
	}
};

var selectedFile= await StorageProvider.SaveFilePickerAsync(options);

If I save a file without manually typing the file extension, selectedFile will not have the file extension, and I have no idea which FilePickerFileType the user selected.