macOS - How to have NSSavePanel to add a file extension in the file name? - swift

Question

I'm using this code to give the user the choice to specify a name and a location where to save a plain text file on disk. All seems to work but the saved file hasn't any extension. Actually I have not specify an extension in any part of my code, I read NSSavePanel documentation without notice the part where explained this option.
Here is the code I'm using:
let textToExport = mainTextField.textStorage?.string
if textToExport != "" {
let mySave = NSSavePanel()
mySave.begin { (result) -> Void in
if result == NSFileHandlingPanelOKButton {
let filename = mySave.url
do {
try textToExport?.write(to: filename!, atomically: true, encoding: String.Encoding.utf8)
} catch {
// failed to write file (bad permissions, bad filename etc.)
}
} else {
NSBeep()
}
}
}

Answer 1

Add the line
mySave.allowedFileTypes = ["txt"]
before presenting the panel.
From the documentation:
The value of this property specifies the file types the user can save
the file as. A file type can be a common file extension, or a UTI. The
default value of this property is nil, which indicates that any file
type can be used. (Note that if the array is not nil and the array
contains no items, an exception is raised.)
If no extension is given by the user, the first item in the
allowedFileTypes array will be used as the extension for the save
panel. If the user specifies a type not in the array, and
allowsOtherFileTypes is true, they will be presented with another
dialog when prompted to save.