Swift: How to determine file type

Using Uniform Type Identifiers (UTIs)

Recently I had to determine what type a given file was for my macOS app Media Explorer. For example, is it an image? a video? or a document? An easy way to do this is by using Uniform Type Identifiers.

A UTI is an identifier that a given extension can fall under to help identify it’s class or type of item. There are broad UTIs such as public.image, and more precise UTIs such as com.apple.quicktime-movie.

We can use these to group together files of a certain type or to identify a certain type of file we are interested in.

First extract the file extension. Given a path, you can do this easily with NSURL:

let extension = NSURL(fileURLWithPath: filePath).pathExtension

Next, convert this into a UTI:

let uti = UTTypeCreatePreferredIdentifierForTag(
    kUTTagClassFilenameExtension,
    extension!,
    nil)

Finally, put this UTI to good use:

if UTTypeConformsTo((uti?.takeRetainedValue())!, kUTTypeImage) {
    print("This is an image!")
}

You can find a list of UTIs at the Mac Developer Library.