Different behavior between addTarget and addGestureRecognizer - swift

Question

I have a function that creates a button with a selector function as a target. The address of a button gets passed to handleSelectPhoto.
lazy var image1Button = createButton(selector: #selector(handleSelectPhoto))
func createButton(selector: Selector) -> UIButton {
let button = UIButton(type: .system)
button.addTarget(self, action: selector, for: .touchUpInside)
return button
}
#objc func handleSelectPhoto(button: UIButton) {
// Do something with button, this works
}
Now, I am trying to change the class of the above from UIButton to UIImageView like the following,
lazy var image1Button = createButton(selector: #selector(handleSelectPhoto))
func createButton(selector: Selector) -> UIImageView {
let view = UIImageView()
view.addGestureRecognizer(UITapGestureRecognizer(target: self, action: selector))
view.isUserInteractionEnabled = true
return view
}
#objc func handleSelectPhoto(button: UIImageView) {
// HERE, button does not get passed
}
With the above changes, in handleSelectPhoto, button instance is not correct. I can not read it as UIImageView type.
If I add a selector function using addGestureRecognizer, does it behave differently than adding a selector function using addTarget, in terms of how selector function is executed with parameters? Maybe I am not understanding how this selector function works...

Answer 1

Adding a target to something like UIGestureRecognizer or UIButton only passes one parameter to the selected function. This parameter depends on the type you are about to add the target on.
In your case the first code snippet works because you are adding a target to an UIButton, so your selected function gets passed this UIButton instance.
In your second scenario you add the target to an UITapGestureRecognizer, so the passed instance will be exactly this gesture recognizer, which cannot be of type UIImageView.
So the difference from the target parameter perspective between UIGestureRecognizer and UIButton is no difference. They both pass their instances to the selected function.
From the UIView subclass perspective there is the difference that UIGestureRecognizer is not a subclass of UIView, but UIButton is. That's why you can just use the passed UIButton instance in your first snippet. In the second snippet you need use the view property of UIGestureRecognizer.
guard let imageView = gestureRecognizer.view as? UIImageView else { return }
Besides your actual question it seems important to clarify how to write #selectors correctly. You're doing it correct already. No change necessary. Some may say you need to add (_:) or : to your selector like so: #selector(handleSelectPhoto(_:)) but this isn't true. In general, you only need to add these special characters when you are selecting a method which has an overload method with a different amount of parameters, but the same base name.

Answer 2

You should make your tell while setting the selection that your function will accept a parameter by adding : at the end of method name.
lazy var image1Button = createButton(selector: #selector(handleSelectPhoto:))
UIKit will automatically understand that the selector methods parameter will be of type UITapGestureRecognizer. Now rewrite the below method like this and you will be good to go.
#objc func handleSelectPhoto(gesture: UITapGestureRecognizer) {
if let buttonImageView = gesture.view as? UIImageView {
//Here you can make changes in imageview what ever you want.
}
}