Question

我创建了一个函数，该函数将从url中获取图像并将其分配给变量，并将该变量作为图像返回。虽然它不返回任何东西并崩溃。

func downloadImage(imageUrl:String) -> UIImage {
        var imageDownloaded : UIImage?
        let configuration = URLSessionConfiguration.default
        let session = URLSession(configuration: configuration)
        let task = session.dataTask(with: URL(string: imageUrl)!) { (data, response, error) in
            if error != nil {
                return
            }
            do {
                imageDownloaded = try UIImage(data: data!)
            } catch {
                print("Fail")
            }
        }
        task.resume()
        return imageDownloaded! //Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value
    }

Answer 1

您试图在变量'imageDownloaded'没有任何值（即nil）时强行解开该变量。发生这种情况是因为下载图像数据需要花费时间。

要解决此问题，您应该使用完成处理程序

func downloadImage(imageUrl:String, @escaping completionHandler: (UIImage?)->()) {
    var imageDownloaded : UIImage?
    let configuration = URLSessionConfiguration.default
    let session = URLSession(configuration: configuration)
    let task = session.dataTask(with: URL(string: imageUrl)!) { (data, response, error) in
        if error != nil {
            return
        }
        do {
            imageDownloaded = try UIImage(data: data!)
            completionHandler(imageDownloaded!)
        } catch {
            print("Fail")
            completionHandler(nil)
        }
    }
    task.resume()
}

尝试使用URLsession从DataTask创建图像不起作用

1 个答案: