ios - CollectionView 加载缓慢

Question

我的 collectionView 从 Firebase 获取数据。有一个 firebase 变量来设置单元格的数量并获取使用 SDWebImage 下载的单元格图像的下载链接。它为每个单元格下载的图像大约为 60 KB，但 collectionview 的加载时间约为 5 秒。此外，当它确实加载时，它会将所有细胞图像显示为第一个细胞图像，然后在一秒钟后更改为正确的图像。

我正在使用 swift 3

这是我的代码

    override func viewDidLoad() {
            super.viewDidLoad()

        //firebase 
        FIRDatabase.database().reference(withPath: "Radio").child("numCells").observeSingleEvent(of: .value, with: { (snapshot) in

            if let snapInt = snapshot.value as? Int {

                self.numCells = snapInt

                self.collectionView?.performBatchUpdates(
                    {
                        self.collectionView?.reloadSections(NSIndexSet(index: 0) as IndexSet)
                }, completion: { (finished:Bool) -> Void in
                })


            }

        }) { (error) in
            print(error.localizedDescription)
        }
    }





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




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

                let icon = cell.viewWithTag(3) as! UIImageView


        //Firebase
        FIRDatabase.database().reference(withPath: "Icons").child("img\(indexPath.row)").child("imgLink").observeSingleEvent(of: .value, with: { (snapshot) in

            if let snapString = snapshot.value as? String {

                icon.sd_setShowActivityIndicatorView(true)
                icon.sd_setIndicatorStyle(.gray)
                icon.sd_setImage(with: URL(string: snapString))
            }

        }) { (error) in
            print(error.localizedDescription)
        }//firebase end



        return cell
    }

Answer 1

不要将 cellForItemAtIndexPath 用于繁重的请求:

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    return collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath)
}

func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
    FIRDatabase.database().reference(withPath: "Icons").child("img\(indexPath.row)").child("imgLink").observeSingleEvent(of: .value, with: { [weak collectionView] (snapshot) in
        guard let collectionView = collectionView else { return }
        let cell = collectionView.cellForItem(at: indexPath)
        /* do whatever you need with cell */
    }) { (error) in
        /* handle error */
    }
}