Swift - NSURL错误

Question

尝试使用NSURL下面的类时出错,下面的代码实际上是试图将我从Facebook拉入的图像存储到imageView.错误如下:

value of optional type 'NSURL?' not unwrapped, did you mean to use '!' or '?' 

不知道为什么会这样,帮忙!

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var myImage: UIImageView!

    override func viewDidLoad() {

        super.viewDidLoad()

        let myProfilePictureURL = NSURL(string: "http://graph.facebook.com/bobdylan/picture")
        let imageData = NSData(contentsOfURL: myProfilePictureURL)
        self.myImage.image = UIImage(data: imageData)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

Answer 1

你正在调用的NSURL构造函数有这个签名:

convenience init?(string URLString: String)

？表示构造函数可能不返回值,因此它被视为可选.

这同样适用于NSData的构造函数:

init?(contentsOfURL url: NSURL)

快速解决方法是:

let myProfilePictureURL = NSURL(string: "http://graph.facebook.com/bobdylan/picture")
let imageData = NSData(contentsOfURL: myProfilePictureURL!)
self.myImage.image = UIImage(data: imageData!)

最好的解决方案是检查(解包)这些选项,即使您确定它们包含值!

您可以在此处找到更多关于选项的信息:链接到官方Apple文档.