Swift NSTextField stringValue not displaying set value - swift

Question

Hello Sultans of Swift!
I am new to Swift although I have used C, C++ and C# a lot. I have come upon a situation that is really puzzling me. I'm going to post a code snippet here:
#IBAction func myFunc(sender: AnyObject)
{
let dirPicker: NSOpenPanel = NSOpenPanel()
dirPicker.allowsMultipleSelection = false
dirPicker.canChooseFiles = true
dirPicker.canChooseDirectories = false
dirPicker.runModal()
let selection = dirPicker.URL
if(selection != nil)
{
do
{
print(selection)
let mp3File = try MP3File(path: (selection?.path)!)
let title = mp3File.getTitle()
// This prints OK
print("Title:\t\(mp3File.getTitle())")
// This prints OK too
print("Title:\t\(title)")
print("Artist:\t\(mp3File.getArtist())")
print("Album:\t\(mp3File.getAlbum())")
print("Lyrics:\n\(mp3File.getLyrics())")
fileName.stringValue = (selection?.path)!
// This sets the label songTitle to an empty space and I can't see why.
// If I initialise title to:
// let title = "STRING CONSTANT"
// ...instead of
// let title = mp3File.getTitle()
// ...then it does actually set the correct text on the label songTitle.
// In both cases, printing to the console works fine! Its just setting
// the text on the label that is eluding me!
songTitle.stringValue = title
}
catch ID3EditErrors.FileDoesNotExist
{
print("Error: File Does Not Exist")
}
catch ID3EditErrors.NotAnMP3
{
print("Error: Not an MP3")
}
catch let e
{
print(e)
}
}
}
When I try to set the text in a label by setting its stringValue property to a variable it just displays empty space, yet I can actually print the variable to the console just fine. The variable is set as the return value of a function. Now if I instead set the variable explicitly to a string constant then it works. So this will be perhaps related to the uncertainty of the return value of the function, but I know it contains the text because I can print it to the console.
Can anyone spot what on earth is happening here?
Thanks
EDIT: I just fixed the comments in the code to refer to songTitle instead of fileName - sorry for the confusion. This is about setting songTitle.stringValue = title
EDIT: This is the definition of songTitle:
#IBOutlet weak var fileName: NSTextField!
#IBOutlet weak var songTitle: NSTextField!
Note that setting the stringValue property of these does actually work so long as I am not using the a variable that is assigned the return value of mp3File.getTitle(). Note also that mp3File.getTitle() does return a value and I can print it to the console OK.

Answer 1

When you have a String value which is printed fine:
print(title) //->I Ran
But cannot be processed well:
songTitle.stringValue = title //->`songTitle` shows nothing!!!
(Of course, you have confirmed that songTitle is fine by assigning constant string to it.)
One possible reason may be existing some control characters in the String.
You can use debugPrint to reveal such cases:
debugPrint(title) //->"\0I Ran\0"
debugPrint uses String literal-like format to show control characters.
In this case, you have NUL characters (U+0000) at both ends.
So, one quick fix is trimming them at each time you get such strings:
Swift 2:
let title = mp3File.getTitle().stringByTrimmingCharactersInSet(NSCharacterSet(charactersInString: "\0"))
Swift 3:
let title = mp3File.getTitle().trimmingCharacters(in: CharacterSet(charactersIn: "\0"))
Or you can write an extension, if you cannot touch the original source of the library:
Swift 2:
extension MP3File {
var title: String {
return self.getTitle().stringByTrimmingCharactersInSet(NSCharacterSet(charactersInString: "\0"))
}
}
Swift 3:
extension MP3File {
var title: String {
return self.getTitle().trimmingCharacters(in: CharacterSet(charactersIn: "\0"))
}
}
(Assuming MP3File does not have a property named title.)
and use it as:
let title = mp3File.title