I'm working on a 3rd party framework for swift so i cannot use the delegate methods of UICollectionViewDelegate myself but I do need them for some custom logic.
Tried multiple approaches to make it work, including method swizzling but in the end I felt like it was too hacky for what i'm doing.
Now i'm subclassing UICollectionView and setting the delegate to an internal (my) delegate.
This works well except for when the UIViewController hasn't implemented the method.
right now my code looks like this:
fileprivate class UICollectionViewDelegateInternal: NSObject, UICollectionViewDelegate {
var userDelegate: UICollectionViewDelegate?
override func responds(to aSelector: Selector!) -> Bool {
return super.responds(to: aSelector) || userDelegate?.responds(to: aSelector) == true
}
override func forwardingTarget(for aSelector: Selector!) -> Any? {
if userDelegate?.responds(to: aSelector) == true {
return userDelegate
}
return super.forwardingTarget(for: aSelector)
}
func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
let collection = collectionView as! CustomCollectionView
collection.didEnd(item: indexPath.item)
userDelegate?.collectionView?(collectionView, didEndDisplaying: cell, forItemAt: indexPath)
}
}
class CustomCollectionView: UICollectionView {
private let internalDelegate: UICollectionViewDelegateInternal = UICollectionViewDelegateInternal()
required init?(coder: NSCoder) {
super.init(coder: coder)
super.delegate = internalDelegate
}
override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
super.init(frame: frame, collectionViewLayout: layout)
super.delegate = internalDelegate
}
func didEnd(item: Int) {
print("internal - didEndDisplaying: \(item)")
}
override var delegate: UICollectionViewDelegate? {
get {
return internalDelegate.userDelegate
}
set {
self.internalDelegate.userDelegate = newValue
super.delegate = nil
super.delegate = self.internalDelegate
}
}
}
In the ViewController I just have a simple set up with the delegate method for didEndDisplaying not implemented
Is it possible to listen to didEndDisplaying without the ViewController having it implemented?
Edit 1:
Here's the code of the ViewController to make it a little more clear what i'm doing
class ViewController: UIViewController {
@IBOutlet weak var collectionView: CustomCollectionView!
override func viewDidLoad() {
super.viewDidLoad()
collectionView.dataSource = self
collectionView.delegate = self
}
}
extension ViewController: UICollectionViewDelegate, UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
1000
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
cell.backgroundColor = .blue
return cell
}
// func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
// print("view controller - did end displaying: \(indexPath.item)")
// }
}
the didEndDisplaying of CustomCollectionView is only triggered when i uncomment the didEndDisplaying method in the ViewController.
what i'm looking for is to have the didEndDisplaying of CustomCollectionView also triggered if the didEndDisplaying method in the ViewController is NOT implemented.
hope it's a little more clear now
Edit 2:
Figured out that the code above had some mistakes which made the reproduction not work as I intended. updated the code above. also made a github page to make it easier to reproduce here: https://github.com/mees-vdb/InternalCollectionView-Delegate
I did a little reading-up on this approach, and it seems like it should work - but, obviously, it doesn't.
Played around a little bit, and this might be a solution for you.
I made very few changes to your existing code (grabbed it from GitHub - if you want to add me as a Collaborator I can push a new branch [same DonMag ID on GitHub]).
First, I implemented didSelectItemAt to make it a little easier to debug (only one event at a time).
ViewController class
class ViewController: UIViewController {
@IBOutlet weak var collectionView: CustomCollectionView!
override func viewDidLoad() {
super.viewDidLoad()
collectionView.dataSource = self
collectionView.delegate = self
}
}
extension ViewController: UICollectionViewDelegate, UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
1000
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
cell.backgroundColor = .blue
return cell
}
// DonMag - comment / un-comment these methods
// to see the difference
//func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
// print("view controller - did end displaying: \(indexPath.item)")
//}
//func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
// print("view controller - didSelectItemAt", indexPath)
//}
}
UICollectionViewDelegateInternal class
fileprivate class UICollectionViewDelegateInternal: NSObject, UICollectionViewDelegate {
var userDelegate: UICollectionViewDelegate?
override func responds(to aSelector: Selector!) -> Bool {
return super.responds(to: aSelector) || userDelegate?.responds(to: aSelector) == true
}
override func forwardingTarget(for aSelector: Selector!) -> Any? {
if userDelegate?.responds(to: aSelector) == true {
return userDelegate
}
return super.forwardingTarget(for: aSelector)
}
func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
let collection = collectionView as! CustomCollectionView
collection.didEnd(item: indexPath.item)
userDelegate?.collectionView?(collectionView, didEndDisplaying: cell, forItemAt: indexPath)
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let collection = collectionView as! CustomCollectionView
collection.didSel(p: indexPath)
userDelegate?.collectionView?(collectionView, didSelectItemAt: indexPath)
}
}
CustomCollectionView class
// DonMag - conform to UICollectionViewDelegate
class CustomCollectionView: UICollectionView, UICollectionViewDelegate {
private let internalDelegate: UICollectionViewDelegateInternal = UICollectionViewDelegateInternal()
required init?(coder: NSCoder) {
super.init(coder: coder)
super.delegate = internalDelegate
}
override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
super.init(frame: frame, collectionViewLayout: layout)
super.delegate = internalDelegate
}
func didEnd(item: Int) {
print("internal - didEndDisplaying: \(item)")
}
func didSel(p: IndexPath) {
print("internal - didSelectItemAt", p)
}
// DonMag - these will NEVER be called,
// whether or not they're implemented in
// UICollectionViewDelegateInternal and/or ViewController
// but, when implemented here,
// it allows (enables?) them to be called in UICollectionViewDelegateInternal
func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
print("CustomCollectionView - didEndDisplaying", indexPath)
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
print("CustomCollectionView - didSelectItemAt", indexPath)
}
override var delegate: UICollectionViewDelegate? {
get {
// DonMag - return self instead of internalDelegate.userDelegate
return self
//return internalDelegate.userDelegate
}
set {
self.internalDelegate.userDelegate = newValue
super.delegate = nil
super.delegate = self.internalDelegate
}
}
}