UIImageWriteToSavedPhotosAlbum(): how to write to the iOS photo album

Swift version: 5.6

Paul Hudson @twostraws May 28th 2019

It's not hard to save an image straight to the user's photo library, but I have to admit the syntax isn't immediately obvious! iOS has a function called UIImageWriteToSavedPhotosAlbum() that takes four parameters: parameter one is the image to save, parameters two and three set a delegate and selector to send when the image has been written successfully, and parameter four is any additional context information you wan to send.

For example, you might use it like this:

UIImageWriteToSavedPhotosAlbum(yourImage, self, #selector(image(_:didFinishSavingWithError:contextInfo:)), nil)

That will write the image to the photo library, then call a method when it completes. That method needs to be named very precisely, which is where it's easy to go wrong. Using the call above, you need to write your callback method like this:

@objc func image(_ image: UIImage, didFinishSavingWithError error: NSError?, contextInfo: UnsafeRawPointer) {
    if let error = error {
        // we got back an error!
        let ac = UIAlertController(title: "Save error", message: error.localizedDescription, preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
    } else {
        let ac = UIAlertController(title: "Saved!", message: "Your altered image has been saved to your photos.", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
    }
}