使用缓存中的图像创建图像数组 (Swift)

Question

我对 iOS 比较陌生，如果在使用扩展程序来帮助管理下载和缓存时，我希望能帮助我弄清楚如何创建图像数组。我已经在这个圈子里转了几个小时，所以认为是时候利用智囊团了。

我创建了 UIImageView 的扩展，以便像这样下载和缓存图像：

let imageCache = NSCache()

extension UIImageView {

func loadImageUsingCacheWithURLString(url: NSURL) {

    self.image = nil

    // First check if there is an image in the cache
    if let cachedImage = imageCache.objectForKey(url) as? UIImage {

        self.image = cachedImage

        return
    }

    else {
    // Otherwise download image using the url location in Google Firebase
    NSURLSession.sharedSession().dataTaskWithURL(url, completionHandler: { (data, response, error) in

        if error != nil {
            print(error)
        }
        else {
            dispatch_async(dispatch_get_main_queue(), {

                // Cache to image so it doesn't need to be reloaded every time the user scrolls and table cells are re-used.
                if let downloadedImage = UIImage(data: data!) {

                    imageCache.setObject(downloadedImage, forKey: url)
                    self.image = downloadedImage

                }
            })
        }
    }).resume()
    }
}

...所以它非常适合加载集合视图图像。但是，我还想捕获一组图像，这样我就可以将它传递给另一个视图控制器，而无需再次下载所有内容（浪费数据）。我创建了另一个函数来执行此操作，但 imageholder.image 始终为零。我不认为这是一个异步问题，因为此时所有图像都被缓存了，当我调试时，我永远无法让它不为零。

var imageHolder: UIImageView!
var imagesArray:[UIImage] = [UIImage]()

// Function to create images array to use on the photo view.
func createImagesArray() {

    for url in imagesURLArray {

        imageHolder.loadImageUsingCacheWithURLString(url)

        if imageHolder.image != nil {

        imagesArray.append(imageHolder.image!)
        }

    }
}

感觉好像我错过了一些简单的东西，但我被卡住了。谢谢！

Answer 1

我最终为返回 UIImage 的扩展创建了另一个函数。这样做之后，附加到 imagesArray 没有问题。

let imageCache = NSCache()
var returnImage:UIImage = UIImage()

func returnImageUsingCacheWithURLString(url: NSURL) -> (UIImage) {

    // First check if there is an image in the cache
    if let cachedImage = imageCache.objectForKey(url) as? UIImage {

        return cachedImage
    }

    else {
        // Otherwise download image using the url location in Google Firebase
        NSURLSession.sharedSession().dataTaskWithURL(url, completionHandler: { (data, response, error) in

            if error != nil {
                print(error)
            }
            else {
                dispatch_async(dispatch_get_main_queue(), {

                    // Cache to image so it doesn't need to be reloaded everytime the user scrolls and table cells are re-used.
                    if let downloadedImage = UIImage(data: data!) {

                        imageCache.setObject(downloadedImage, forKey: url)
                        returnImage = downloadedImage

                    }
                })
            }
        }).resume()
        return returnImage
    }
}

Answer 2

let imageCache = NSCache()
let images:[UIImages] = []

extension UIImageView {

func loadImageUsingCacheWithURLString(url: NSURL) {

    self.image = nil

    // First check if there is an image in the cache
    if let cachedImage = imageCache.objectForKey(url) as? UIImage {

        self.image = cachedImage

        return
    }

    else {
    // Otherwise download image using the url location in Google Firebase
    NSURLSession.sharedSession().dataTaskWithURL(url, completionHandler: { (data, response, error) in

        if error != nil {
            print(error)
        }
        else {
            dispatch_async(dispatch_get_main_queue(), {

                // Cache to image so it doesn't need to be reloaded every time the user scrolls and table cells are re-used.
                if let downloadedImage = UIImage(data: data!) {

                    imageCache.setObject(downloadedImage, forKey: url)
                    self.image = downloadedImage

                }
            })
        }
        }).resume()
    }
    //Creat array and append the last image to it. 
    self.images.append(self.image)
}