ios - Collection View 加载不稳定

Question

我有一个从 API 加载数据的 Collection View 。 Collection View 工作正常，除了它只在滚动时加载图像。我试过异步加载图像，但差别很小。我想要加载所有图像或在图像加载之前预加载图像？我正在使用 Haneke 从 URL 加载图像。这是我在 Collection View 中使用的代码:

  func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return self.tableData.count
}

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
    let cell: ProductsViewCell = collectionView.dequeueReusableCellWithReuseIdentifier("productViewCell", forIndexPath: indexPath) as! ProductsViewCell

    let rowData = tableData[indexPath.row]

    cell.backgroundColor = UIColor.whiteColor()

    for (key,value) in rowData {
        cell.productPrice.text = value["merged"][0]["variants"][0]["price"].string
        cell.productName.text = value["merged"][0]["title"].string


        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
            if let imageString = value["merged"][0]["images"][0]["src"].string {
                let url = NSURL(string: imageString)

                dispatch_async(dispatch_get_main_queue(), {
                    cell.productImage.contentMode = .ScaleAspectFill
                    cell.productImage.hnk_setImageFromURL(url!)
                })
            }
        })


        if let variantData =  value["merged"][0]["variants"].array {
            var sum = 0

            for variant in variantData {
                sum += variant["inventory_quantity"].int!
            }

            if sum <= 0 {
                cell.soldOut.hidden = false

            } else {
                cell.soldOut.hidden = true
            }
        }


    }

    return cell
}

func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
    print("Cell \(indexPath.row) selected")
}

Answer 1

您想要完成主线程的所有下载，然后在图像或图像数据可用时分派(dispatch)到主队列以更新 UI。在这里，您的方向是正确的，但您是在主线程上下载。改变这个:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
            if let imageString = value["merged"][0]["images"][0]["src"].string {
                let url = NSURL(string: imageString)

                dispatch_async(dispatch_get_main_queue(), {
                    cell.productImage.contentMode = .ScaleAspectFill
                    cell.productImage.hnk_setImageFromURL(url!)
                })
            }
        })

收件人:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
            if let imageString = value["merged"][0]["images"][0]["src"].string {
                let url = NSURL(string: imageString)
                let imageData = NSData(contentsOfURL: imageString)
                let image = UIImage(data: imageData)

                dispatch_async(dispatch_get_main_queue(), {
                    cell.productImage.contentMode = .ScaleAspectFill
                    cell.productImage.image = image
                })
            }
        })