How do you access a UIViewController function from within a UICollectionCell?

Question

I have a function within a UICollectionViewCell that requires access to the hosting UIViewController. Currently 'makeContribution()' can't be accessed:

What is the proper way of accessing the host UIViewController that has the desired function?

Answer 1

Thanks to the insightful responses, here's the solution via delegation:

...

...

...

{makeContribution}

Answer 2

This is a mildly controversial question - the answer depends a little on your philosophy about MVC. Three (of possibly many) options would be:

1. Move the @IBAction to the view controller. Problem solved, but it might not be possible in your case.

2. Create a delegate. This would allow the coupling to be loose - you could create a ContributionDelegate protocol with the makeContribution() method, make your view controller conform to it, and then assign the view controller as a weak var contributionDelegate: ContributionDelegate? in your cell class. Then you just call:

   contributionDelegate?.makeContribution()
   

3. Run up the NSResponder chain. This answer has a Swift extension on UIView that finds the first parent view controller, so you could use that:

   extension UIView {
       func parentViewController() -> UIViewController? {
           var parentResponder: UIResponder? = self
           while true {
               if parentResponder == nil {
                   return nil
               }
               parentResponder = parentResponder!.nextResponder()
               if parentResponder is UIViewController {
                   return (parentResponder as UIViewController)
               }
           }
       }
   }
   
   // in your code:
   if let parentVC = parentViewController() as? MyViewController {
       parentVC.makeContribution()
   }
   

Answer 3

Well, CollectionView or TableView?

Anyway, Set your ViewController as a delegate of the cell. like this:

@objc protocol ContributeCellDelegate {
     func contributeCellWantsMakeContribution(cell:ContributeCell)
}

class ContributeCell: UICollectionViewCell {

    // ...

    weak var delegate:ContributeCellDelegate?

    @IBAction func contributeAction(sender:UISegmentedControl) {
        let isContribute = (sender.selectedSegmentIndex == 1)

        if isContribute {
            self.delegate?.contributeCellWantsMakeContribution(self)
        }
        else {
        }
    }
}


class ViewController: UIViewController, UICollectionViewDataSource, ContributeCellDelegate {

    // ...

    func collectionView(_ collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        cell = ...

        if cell = cell as? ContributeTableViewCell {
            cell.delegate = self
        }

        return cell
    }

    // MARK: ContributeCellDelegate methods

    func contributeCellWantsMakeContribution(cell:ContributeCell) {
        // do your work.
    }
}