"Missing argument for parameter 'for' in call"

Question

Whilst coding in swift3 I wanted to use custom protocols and generics for reusing collection view cells. I know that this is the standard way of reusing cells:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "TacoCell", for: indexPath) as? TacoCell {

        cell.configureCell(taco: ds.tacoArray[indexPath.row])

        return cell
    }

    return UICollectionViewCell()
}

But everytime I try to do this:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(forIndexPath: indexPath) as TacoCell
    cell.configureCell(taco: ds.tacoArray[indexPath.row])
    return cell
}

The compiler complains I have a "Missing argument for parameter 'for' in call"... The parameter in this case is "forIndexPath"

FYI...

I have custom extensions for reusing cells and loading nibs. Code is as follows:

ReusableView class

import UIKit

protocol ReusableView: class  { }

extension ReusableView where Self: UIView {

    static var reuseIdentifier: String {
        return String.init(describing: self)
    }
}

NibLoadableView class

import UIKit

protocol NibLoadableView: class { }

extension NibLoadableView where Self: UIView {

    static var nibName: String {
        return String.init(describing: self)
    }
}

This is my extension for the UICollectionView

import UIKit

extension UICollectionView {
    func register<T: UICollectionViewCell>(_: T.Type) where T: ReusableView, T: NibLoadableView {

    let nib = UINib(nibName: T.nibName, bundle: nil)
    register(nib, forCellWithReuseIdentifier: T.reuseIdentifier)
}


func dequeueReusableCell<T: UICollectionViewCell>(forIndexPath indexPath: NSIndexPath) -> T where T: ReusableView {

    guard let cell = dequeueReusableCell(withReuseIdentifier: T.reuseIdentifier, for: indexPath as IndexPath) as? T else {
        fatalError("Could not dequeue cell with identifier: \(T.reuseIdentifier)")
    }

    return cell
    }
}

extension UICollectionViewCell: ReusableView { }

Could you provide a link for the description of `dequeueReusableCell` that uses (only) `forIndexPath`? Also, have you tried replacing `forIndexPath` with `for`? — , Sep 07 '16 at 06:19
Sorry @Evert... I made an extension of the UICollectionView and I am using my"overrided" `dequeueReusableCell` method which has the argument `forIndexPath`. My assumption was since it was accepted as an extension, I could use it to reuse my cells. I included the extension code above as well — CommittedEel, Sep 07 '16 at 06:31

score 2 · Accepted Answer · answered Sep 07 '16 at 10:16

The problem is that you've got a little bit of Swift 2.2 code alongside your Swift 3.0 code, and the compiler is getting confused when it tries to pick a method to call because nothing quite matches.

Your cellForItemAt method calls your own dequeueReusableCell() extension method with the IndexPath from the collection view. However, the extension method you wrote expects to receive an NSIndexPath, which is a subtly different thing.

Amend your extension method to this and the problem should clear up:

func dequeueReusableCell<T: UICollectionViewCell>(forIndexPath indexPath: IndexPath) -> T where T: ReusableView {

Thank you @TwoStraws! That seemed to get it going – CommittedEel Sep 08 '16 at 02:07 — CommittedEel, Sep 08 '16 at 02:07

"Missing argument for parameter 'for' in call"

1 Answers1