Question

我有一系列链接到图像文件的URL，如何将它们存储到UIImages数组中？

var imagesArray = [UIImage]()

let links = ["http://example.com/image1.jpg","http://example.com/image2.jpg"] as [String]

必须有一个简单的解决方案。如果是一张图片，我可以做如下的事情：

let url = URL(string: link2image!)!
let imageData = try? Data(contentsOf: url)
let image = UIImage(data: imageData!)!
self.image.append(image)

Answer 1

最简单的解决方案是迭代数组并使用Data(contentsOf:)同步下载图像，但是，由于同步执行，这将是非常不充分的。

let images = links.flatMap{ link->UIImage? in
    guard let url = URL(string: link) else {return nil}
    guard let imageData = try? Data(contentsOf: url) else {return nil}
    return UIImage(data: imageData)
}

更好的解决方案是并行异步下载图像，我使用PromiseKit为此编写了UIImage扩展名：

extension UIImage {
    class func downloadedAsync(fromUrl url: URL)->Promise<UIImage> {
        return Promise{ fulfill, reject in
            URLSession.shared.dataTask(with: url, completionHandler: { data, response, error in
                guard let data = data, error == nil else {
                    reject(error!); return
                }
                guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
                    reject(NSError(domain: "Wrong HTTP response code when downloading image asynchronously",code: (response as? HTTPURLResponse)?.statusCode ?? 1000));return
                }
                guard let mimeType = response?.mimeType, mimeType.hasPrefix("image"), let image = UIImage(data: data) else {
                    reject(NSError(domain: "No image in response", code: 700)); return
                }
                fulfill(image)
            }).resume()
        }
    }
}

你可以通过这样的链接来调用它：

var imageDownloadTasks = links.flatMap{ link in
    guard let url = URL(string: link) else {return nil}
    return UIImage.downloadedAsync(fromUrl: url)
}

然后执行承诺：

when(fulfilled: imageDownloadTasks).then{ images in
    //use the images, images is of type [UIImage]
}

Answer 2

也许你可以尝试使用函数式编程：map closure ...

links.map({
    if let imageData = try? Data(contentsOf: URL(string: $0)!) {
        UIImage(data: imageData)
    }
})

但你必须知道你的链接是否错误，它会崩溃。所以，我建议你做一些防范以防止这些崩溃。像这样...

guard let url = URL(string: $0) else { return nil }

将URL数组转换为UIImage数组

2 个答案: