ios - 从循环中的 URL 下载图像以获取 Collection View

Question

我正在尝试创建图像的 Collection View 。我已经尝试了这些解决方案来下载图像:
one
two
three
还有
four

var tempObject = json["photos"]
                for var i = 0; i < tempObject.count; i++
                {
                    var tempImage = UIImage()

                    dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {

                        tempImage =  UIImage(data: NSData(contentsOfURL: NSURL(string:"https://developer.apple.com/swift/images/swift-og.png")!)!)!
                    })

                    swiftImages.insert(tempImage, atIndex: i)
                }

                dispatch_async(dispatch_get_main_queue()) {

                    self.collectionView?.reloadData()
                }

但我无法让它显示图像。我是 swift 网络的新手。

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell", forIndexPath: indexPath) as! ImageCollectionViewCell
        cell.imageView.image = swiftImages[indexPath.row]
        return cell
    }

Answer 1

您正在将 UIImage()(在 dispatch_async block 之前创建的)对象添加到 swiftImages 数组。请注意 dispatch_async block 会在未来某个时间执行，它不会在 var tempImage = UIImage() 行之后立即执行。从 dispatch block 中获取图像，这也是您应该将 dispatch 发送到主队列以重新加载集合的地方。像这样更改您的代码:

            var tempObject = json["photos"]
            for var i = 0; i < tempObject.count; i++
            {
                dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {

                    var tempImage =  UIImage(data: NSData(contentsOfURL: NSURL(string:"https://developer.apple.com/swift/images/swift-og.png")!)!)!
                    swiftImages.insert(tempImage, atIndex: i)
                    dispatch_async(dispatch_get_main_queue()) {

                       self.collectionView?.reloadData()
                    }
                })
            }

顺便说一句，为 Collection View 或表格 View 单元格加载图像不仅仅是阅读图像，有时您可能会使用类似 AlamofireImage 的东西。 .