为什么在尝试使用自己的CollectionViewCell类时出现此错误？

Question

1.I'm putting a UICollectionView into a UIView .

2.I'm using my own UICollectionViewCell class.

3.The error is "Type 'TimeLineViewController' does not conform to protocol UICollectionViewDataSource "

4.If I change the return type of func collectionView(collectionView: UICollectionView , cellForItemAtIndexPath indexPath: NSIndexPath) to UICollectionViewCell , there would not be error.

Here are my codes:

import UIKit

class TimeLineViewController: UIViewController, UICollectionViewDataSource,UICollectionViewDelegate {

@IBOutlet weak var TimeLineColleciontView: UICollectionView!

// TODO TODO set cell size permeantly
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    return CGSize(width: collectionView.frame.width-20,
        height: (collectionView.frame.width-20) * 1.2 )
}

func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 3
}

func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
    return 1
}


func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> TimeLineCollectionViewCell {
    let id = "TimeLineCell"
    let cell = collectionView.dequeueReusableCellWithReuseIdentifier(id, forIndexPath: indexPath) as! TimeLineCollectionViewCell
    return cell
}

override func preferredStatusBarStyle() -> UIStatusBarStyle {
    return UIStatusBarStyle.LightContent
}

override func viewDidLoad() {
    super.viewDidLoad()
    self.TimeLineColleciontView.backgroundColor = UIColor(white: 0, alpha: 0)

    TimeLineColleciontView.dataSource = self
    TimeLineColleciontView.delegate = self

    // 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.
}


}

And my cell class is simple:

import UIKit

class TimeLineCollectionViewCell: UICollectionViewCell {

var cover : UIImageView = UIImageView()
var date : UILabel = UILabel()

override func awakeFromNib() {
    cover.frame = CGRect(x: 0, y: 0, width: self.frame.width, height: self.frame.width)
    date.frame = CGRect(x: 0, y: 0, width: 300, height: 300)
    self.insertSubview(cover, atIndex: 0)
    self.insertSubview(date, atIndex: 2)
}
}

Answer 1

For TimeLineViewController class to conform to UICollectionViewDataSource protocol, you are supposed to return a UICollectionViewCell for the cellForItemAtIndexPath function. Since you have changed the function signature (return type) to TimeLineCollectionViewCell , you are getting this error.

Make the return type of your cellForItemAtIndexPath function as UICollectionViewCell and return the dequeued instance of TimeLineCollectionViewCell within your function. Since UICollectionViewCell is the parent class of TimeLineCollectionViewCell , you will not see the error.

Note: You will have to cast the returned UICollectionViewCell value from cellForItemAtIndexPath to TimeLineCollectionViewCell wherever necessary