选择CollectionView Swift4中的第一个项目

Question

我正在尝试在CollectionView加载时选择CollectionView中的第一个项目。我找到了Swift 3的许多解决方案，但是在Swift4中对我有任何帮助。我尝试的(ViewDidappear(：

import UIKit
import SDWebImage
class PostsTab_Details: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
@IBOutlet weak var PostsSelectRarityCollectionView: UICollectionView!
@IBOutlet weak var RarityTypeLbl: UILabel!
//Center my Collectionview Horizontal
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        let totalCellWidth = 100 * (selectedPosts?.rarity.count)!
        let totalSpacingWidth = 10 * (3 - 1)
        let leftInset = (PostsSelectRarityCollectionView.frame.width - CGFloat(totalCellWidth + totalSpacingWidth)) / 2
        let rightInset = leftInset
        return UIEdgeInsetsMake(0, leftInset, 0, rightInset)
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return (selectedPosts?.rarity.count)!
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell =  PostsSelectRarityCollectionView.dequeueReusableCell(withReuseIdentifier: "PostssTab_DetailCollectionCell", for: indexPath) as! PostsTab_DetailsCollectionViewCell
    cell.PostssTab_DetailCollectionImage.sd_setImage(with: URL(string: (selectedPosts?.PostsImageURL)!))

    return cell
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    RarityTypeLbl.text = selectedPosts?.rarity[indexPath.row].rarity
}
 //Tried this also with IndexPath(item: 0, section: 0)
override func viewDidAppear(_ animated: Bool) {
    let selectedIndexPath = IndexPath(row: 0, section: 0)
    PostsSelectRarityCollectionView.selectItem(at: selectedIndexPath, animated: true, scrollPosition: .right)
}

var selectedPosts: Posts?
override func viewDidLoad() {
    PostsSelectRarityCollectionView.delegate = self
    PostsSelectRarityCollectionView.dataSource = self
}
}

但这不起作用...我希望有人知道我在做什么错。

预先感谢

更新：现在，这对我有用，这要归功于拉齐布的答案：

override func viewWillAppear(_ animated: Bool) {
    self.collectionView(PostsSelectRarityCollectionView, didSelectItemAt: IndexPath(row: 0, section: 0))
}

Answer 1

您的代码对我来说似乎还可以。如果您想触发 didSelectItemat 方法，请使用以下代码。

 override func viewDidAppear(_ animated: Bool) {
    self.PostsSelectRarityCollectionView(self.PostsSelectRarityCollectionView, didSelectItemAt: IndexPath(row: 0, section: 0))
}

Answer 2

在CollectionViewCell中以编程方式选择CollectionView Loads您应该在ViewDidAppear中进行代码时：

override func viewDidAppear(_ animated: Bool) {
    let indexPath:IndexPath = IndexPath(row: 0, section: 0)
    collectionView?.selectItem(at: indexPath, animated: false, scrollPosition: .top)
}

Answer 3

尝试此(swift 5(：

    let indexPath:IndexPath = IndexPath(row: 0, section: 0)
    collectionView?.selectItem(at: indexPath, animated: false, scrollPosition: .top)