CODEWITHSUNDEEP
iosswiftuicollectionviewuicollectionviewcell
BigBoy1337
BigBoy1337

Reputation: 4963

How to implement nested collection views?

I am following this famous tutorial and would like to instead implement a collectionView inside of another collectionView. I think I almost have it with this in my ViewController.swift: 

import UIKit

class ViewController: UIViewController, UICollectionViewDelegate,UICollectionViewDataSource {
    let model: [[UIColor]] = generateRandomData()

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return model.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "outerCell", for: indexPath) as! OuterCollectionViewCell
        return cell
    }

    func collectionView(_ collectionView: UICollectionView,
                        willDisplay cell: UICollectionViewCell,
                        forItemAt indexPath: IndexPath){
        guard let outerCollectionViewCell = cell as? OuterCollectionViewCell else { return }
        outerCollectionViewCell.setCollectionViewDataSourceDelegate(dataSourceDelegate: self, forRow: indexPath.row)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

extension ViewController: UICollectionViewDelegate, UICollectionViewDataSource {
    func collectionView(collectionView: UICollectionView,
                        numberOfItemsInSection section: Int) -> Int {

        return model[collectionView.tag].count
    }

    func collectionView(collectionView: UICollectionView,
                        cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell",
                                                                         forIndexPath: indexPath)

        cell.backgroundColor = model[collectionView.tag][indexPath.item]

        return cell
    }
}

Then: 

class OuterCollectionViewCell: UICollectionViewCell {
    @IBOutlet weak var innerCollectionView: UICollectionView!

    func setCollectionViewDataSourceDelegate
        <D: UICollectionViewDataSource & UICollectionViewDelegate>
        (dataSourceDelegate: D, forRow row: Int) {

        innerCollectionView.delegate = dataSourceDelegate
        innerCollectionView.dataSource = dataSourceDelegate
        innerCollectionView.tag = row
        innerCollectionView.reloadData()
    }
}

However Xcode is angry: Redundant conformance of ViewController to protocol UICollectionViewDataSource and UICollectionViewDelegate. This is understandable as I am defining it twice..

How do I specify the difference between delegate methods for the inner and outer collectionViews here?

Upvotes: 0

Views: 1316

Answers (1)

Shehata Gamal
Shehata Gamal

Reputation: 100503

Sure there is a redundancy because this

1-

class ViewController: UIViewController, UICollectionViewDelegate,UICollectionViewDataSource

with this 

extension ViewController: UICollectionViewDelegate, UICollectionViewDataSource {

the VC should conform only once for these protocols

2-

you need to only implement one copy of each method and check the name of the collectionView in it

func collectionView(collectionView: UICollectionView,
                    numberOfItemsInSection section: Int) -> Int {

     if collectionView == mainCollectionView {
        return  model.count // this is the VC collection
     }
     else {
        return model[collectionView.tag].count  // cells collection
      }

}

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

   if collectionView == mainCollectionView {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "outerCell", for: indexPath) as! OuterCollectionViewCell
        return cell
    }
    else {

        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell",forIndexPath: indexPath)
        cell.backgroundColor = model[collectionView.tag][indexPath.item]
        return cell

    }
}

func collectionView(_ collectionView: UICollectionView,
                    willDisplay cell: UICollectionViewCell,
                    forItemAt indexPath: IndexPath){


   if collectionView == mainCollectionView {

        guard let outerCollectionViewCell = cell as? OuterCollectionViewCell else { return }
       outerCollectionViewCell.setCollectionViewDataSourceDelegate(dataSourceDelegate: self, forRow: indexPath.row)
   }
}

Upvotes: 1

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