ios - uicollectionview 不快速显示单元格

Question

我从 url 中获取数据作为 json 字符串。在我的代码中，titles 变量是我的url 图片的数组。

private let reuseIdentifier = "cell_supporters"

class SupportersCollectionViewController: UICollectionViewController {
    var ids             = [String]()
    var titles          = [String]()

    @IBOutlet var collection_supporters: UICollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()

        collection_supporters.delegate = self

        // Register cell classes
        self.collectionView!.register(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)

        getSupporters()
    }

    // MARK: UICollectionViewDataSource

//    override func numberOfSections(in collectionView: UICollectionView) -> Int {
//        // #warning Incomplete implementation, return the number of sections
//        return 1
//    }


    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        // #warning Incomplete implementation, return the number of items
        return self.titles.count
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath as IndexPath) as! SupportersCollectionViewCell

        print("Hello collectionView")

        let url_img = URL(string: self.titles[indexPath.row])!

        print(url_img)
        cell.img_logo.af_setImage(
            withURL: url_img
        )

        return cell
    }

    func getSupporters() {
        RestApiManager.sharedInstance.getSupporters { (json: JSON) in
            if let results = json.array {
                for entry in results {
                    // print(entry["title"])
                    //self.ids.append(entry["id"].string!)
                    self.titles.append(entry["title"].string!)
                }

                print(self.titles.count)

                DispatchQueue.main.async{
                    self.collection_supporters.reloadData()
                }
            }
        }
    }
}

---

在我的代码中:

print(self.titles.count) // it shows 5

但是:

print("Hello collectionView") // not show anything !

Answer 1

如果您为布局使用默认的 UICollectionViewFlowLayout 类，您可以尝试实现返回 collectionView 中每个项目大小的委托(delegate)方法。如果 UICollectionView 没有大小信息或它们为零，则它根本不会调用 cellForItemAt dataSource 方法。

尝试添加这个:

extension SupportersCollectionViewController: UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: 40, height: 40) // Return any non-zero size here
    }
}