为啥未显示集合可重用视图？

Posted 2023-03-14

【中文标题】为啥未显示集合可重用视图？

【英文标题】：Why Collection Reusable View not shown?为什么未显示集合可重用视图？

【发布时间】：2017-05-16 15:13:49

【问题描述】：

我想创建带有标题的 UICollectionView。我在 mainStoryBoard 上设置了 Collection Reusable View，但设备上没有显示任何内容。我试图搜索但找不到它为什么没有出现。我

主要故事板

在设备上

导入 UIKit

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate 


    @IBOutlet weak var collectionView: UICollectionView!

    var images = ["medal1","medal2","medal3","medal4","medal5","medal6","medal7","medal8","medal9","medal10","medal1","medal2","medal3","medal14"]

    var texts = ["hi","yes","hoo","such","hi","yes","hoo","such","hi","yes","hoo","such","hi","yes"]

    override func viewDidLoad() 
        super.viewDidLoad()



        collectionView.delegate = self
        collectionView.dataSource = self

    

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

        return images.count
    

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

        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CustomCell", for: indexPath) as! CustomCell

        cell.myImage.image = UIImage(named: images[indexPath.row])

        cell.achievementLabel.text = texts[indexPath.row]

        return cell

    

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









import UIKit

集合视图类 类 CustomCell: UICollectionViewCell

    @IBOutlet weak var myImage: UIImageView!

    @IBOutlet weak var achievementLabel: UILabel!

集合可重用视图的类 导入 UIKit

class CollectionReusableView: UICollectionReusableView 

    @IBOutlet weak var reuseableVimage: UIImageView!



> import UIKit

class ViewController: UIViewController, UICollectionViewDelegate 


    @IBOutlet weak var collectionView: UICollectionView!

    var images = ["medal1","medal2","medal3","medal4","medal5","medal6","medal7","medal8","medal9","medal10","medal1","medal2","medal3","medal14"]

    var texts = ["hi","yes","hoo","such","hi","yes","hoo","such","hi","yes","hoo","such","hi","yes"]

    override func viewDidLoad() 
        super.viewDidLoad()



        collectionView.delegate = self


    

    func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView 
        if kind == UICollectionElementKindSectionHeader 
            let view = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: "HeaderView", for: indexPath)
            // do any programmatic customization, if any, here
            return view
        
        fatalError("Unexpected kind")

【参考方案1】：

你必须实现viewForSupplementaryElementOfKind:

针对UICollectionElementKindSectionHeader 或UICollectionElementKindSectionFooter 酌情实施collectionView(_:viewForSupplementaryElementOfKind:at:)。

func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView 
    if kind == UICollectionElementKindSectionHeader 
        let view = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: "CollectionReusableView", for: indexPath) as! CollectionReusableView
        // do any programmatic customization, if any, here
        return view
    
    fatalError("Unexpected kind")

确保 IB 中的标题可重用视图具有

适当的基类；和 适当的“重用标识符”

在 IB 中，确保集合视图的“附件”在“Section Header”和“Section Footer”旁边有复选标记。

【讨论】：

谢谢。我更新了代码，但现在屏幕什么也没显示。我检查了 IB 和附件，一切都很好。

假设没有警告，我可能会检查视图调试器，看看集合视图中是否有视图以及它们的框架是什么。如果真的没有视图，那么我会在 UICollectionViewDataSource 方法中设置断点并查看它们是否被调用以及它们返回的值。

当我设置 collectionView.dataSource = self 时，它会迷恋。

这是断点 ""let view = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: "CollectionReusableView", for: indexPath) as！ CollectionReusableView""

听起来像是标题视图没有匹配的“重用标识符”或标题的基类尚未设置。

【参考方案2】：

尝试实现这一点。 RayWenderlich 中有一个可能对您有用的示例：https://www.raywenderlich.com/136161/uicollectionview-tutorial-reusable-views-selection-reordering

override func collectionView(_ collectionView: UICollectionView,
                             viewForSupplementaryElementOfKind kind: String,
                             at indexPath: IndexPath) -> UICollectionReusableView 
switch kind 
case UICollectionElementKindSectionHeader:
    let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: kind,
                                                                           withReuseIdentifier: "CollectionReusableView",
                                                                           for: indexPath) as! CollectionReusableView
    headerView.reuseableVimage ....
    return headerView
default:
    assert(false, "Unexpected element kind")

【讨论】：

看来swift 3有一些变化：/