I'm trying to find some way in Cocoa to translate from file extensions to Uniform Type Identifiers. That is, I want to find some way of doing this:
".jpg" => "public.jpeg"
".html" => "public.html"
".ttf"=> "public.truetype-font"
I've searched on the NSWorkspace docs but couldn't find anything. The closest I could get was:
- (NSImage *)iconForFileType:(NSString *)fileType
that returns the icon for a file extension, and
– (NSString *)preferredFilenameExtensionForType:(NSString *)typeName
that does exactly the opposite of what I'm trying to do. Do any of you know how to do this?
I really hope I don't have to check for a lot of extensions by hand.
Thanks in advance.
I needed this about a week ago:
NSString * UTI = (NSString *)UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension,
(CFStringRef)[myFilePath pathExtension],
NULL);
If I run this on the extensions @"php", @"jpg", @"html", and @"ttf", it prints:
public.php-script
public.jpeg
public.html
public.truetype-ttf-font
Update 11+ years later:
In Swift, there are two ways to do this, depending on your deployment target:
If you want to run on macOS Catalina and earlier (before Big Sur) or iOS 13 and earlier:
let fileExtension = "html"
let unmanagedString = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension as CFString,
fileExtension as CFString,
nil)
let typeIdentifier = unmanagedString?.takeRetainedValue() as String?
The UTTypeCreatePreferredIdentifierForTag()
func (still part of the CoreServices
module) returns an Unmanaged<CFString>?
; this is a type that boxes a CFString
and you need to indicate (via one of the .take...
methods) what the memory management semantics should be.
Since the function follows the Create Rule naming pattern, it's going to return a CFString
to us that we need to take ownership of. Therefore we use .takeRetainedValue()
to transfer the ownership of the CFString
from the manual memory management world into the ARC world.
Then there's a decent amount of bridging to go from String
to CFString
and vice versa.
macOS Big Sur (and iOS 14) got a new UniformTypeIdentifiers
module that makes this a whole lot simpler:
let fileExtension = "html"
let typeIdentifier = UTType(filenameExtension: fileExtension)