Question

我试图在Collectionview加载时选择CollectionView中的第一个项目。我找到了许多Swift 3的解决方案，但在Swift4中没有任何对我有用的东西。我尝试了什么（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......我希望有人知道我做错了什么......

提前致谢

更新由于Razib的回答，这对我现在很有用：

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

Answer 1

要在加载Collectionview时以编程方式选择CollectionViewCell中的第一个项目，应在viewDidAppear中进行编码：

True

Answer 2

你的代码对我来说似乎没问题。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 3

尝试一下（快速5）：

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

在CollectionView Swift4中选择第一个项目

3 个答案: