How to save a file of user-defined format/extension?

Question

My App allows the user to directly operate on the raw binary of a file, so the user may want to save the file with any extension. However, FileSavePicker does not allow a wildcard extension.
Currently, I have to show a flyout containing a textbox, requiring the user to type the extension to save as. But this behavior I feel is somewhat strange.
Any better workaround?

Answer 1

Hello, Welcome to Micorosoft Q&A,

How to save a file of user-defined format/extension?

As you mentioned above, FileSavePicker does not allow a wildcard extension, for this scenario, the better way is launch the FileSavePicker with extension programmatic， you could package the FileSavePicker with extension parameter.

For example

private async Task<StorageFile> PickFileAsync(string extension)  
{  
    var picker = new FileSavePicker();  
    picker.SuggestedStartLocation = PickerLocationId.Downloads;  
    picker.SuggestedFileName = "saved file";  
    picker.DefaultFileExtension = ".txt";  
    picker.FileTypeChoices.Add("file", new List<string> { extension });  
  
    var file = await picker.PickSaveFileAsync();  
    return file;  
}  

Usage

var file =  await PickFileAsync(".pp");  

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