Swift单例类中imagePickedBlock属性类型咨询

Great question—let’s break this down clearly using your code as a reference. First, here’s the key snippet from your singleton:

class CameraHandler: NSObject, UIImagePickerControllerDelegate {
    static let shared = CameraHandler()
    
    //MARK: Internal Properties
    var imagePickedBlock: ((UIImage) -> Void)? ///// What kind of property is THIS ???
    
    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
        if let image = info[UIImagePickerControllerOriginalImage] as? UIImage {
            self.imagePickedBlock?(image)
        } else{
            print("Something went wrong")
        }
    }
}

And your calling code:

CameraHandler.shared.imagePickedBlock = { (image) in
    /* get your image here */
    print("Got image!!!!")
}

Now, let’s define exactly what imagePickedBlock is:

• It’s an optional stored closure property
  The type ((UIImage) -> Void)? tells us:

  • The core type is a closure that accepts a single UIImage parameter and returns no value (marked by -> Void).
  • The trailing ? makes it an optional, so it starts as nil until you assign a closure to it (like you do in your calling code).
  • Since it’s declared with var instead of let, it’s mutable—you can reassign different closures to it at runtime if needed.

• Functionally, it’s a callback mechanism
  This property exists to handle asynchronous results from the image picker. Since waiting for a user to select an image isn’t an immediate action, the closure acts as a "callback": once the user finishes picking a photo, the imagePickerController(_:didFinishPickingMediaWithInfo:) method triggers the closure, passing the selected image directly to the code that needs it. The ? in self.imagePickedBlock?(image) safely runs the closure only if you’ve assigned one (avoiding crashes if it’s still nil).

In short, it’s a mutable, optional stored property that holds a closure for asynchronous image selection callbacks.

内容的提问来源于stack exchange，提问作者Mudith Chathuranga Silva