Question

我无法获得以下代码进行编译，有人建议吗？

import UIKit

class ViewController: UIViewController, UIScrollViewDelegate {

    @IBOutlet weak var avatar: UIImageView!
    @IBOutlet weak var scrollView: UIScrollView!
    @IBOutlet weak var contentImageView: UIImageView!

    override func viewDidLoad() {
        super.viewDidLoad()
        avatar.layer.cornerRadius = 5.0
        avatar.layer.borderWidth = 4.0
        avatar.layer.borderColor = UIColor.whiteColor().CGColor
        avatar.clipsToBounds = true
        scrollView.delegate = self
        contentImageView.clipsToBounds = true
    }

    override func viewDidAppear(animated: Bool) {
        let vc = self.storyboard?.instantiateViewControllerWithIdentifier("LoginScreen") as! UIViewController
        self.presentViewController(vc, animated: true, completion: nil)
    }

    func scrollViewDidScroll(scrollView: UIScrollView) {
        let yOffset = self.scrollView.contentOffset.y * 0.2
        let availableOffset = min(yOffset, 60)
        let contentRectYOffset = availableOffset / contentImageView.frame.size.height
        contentImageView.layer.contentsRect = CGRectMake(0.0, contentRectYOffset, 1, 1);
    }
}

错误

'来自'UIViewController的'Downcast？' 'UIViewController'只能解开自选项目;你的意思是使用'！'

这发生在

行中

let vc = self.storyboard?.instantiateViewControllerWithIdentifier("LoginScreen") as! UIViewController

Answer 1

你强行抛弃一个已经是同一类型的对象。您只需删除as! UIViewController并假设标识为ViewController的{{1}}存在，您可以在需要时强制解包LoginScreen变量。

vc

Answer 2

感谢R P，您的解决方案很有效。

override func viewDidAppear(animated: Bool) {
let vc = self.storyboard?.instantiateViewControllerWithIdentifier("LoginScreen")
self.presentViewController(vc!, animated: true, completion: nil)

}

错误 - UIImageView UIScrollView播放背景视频

2 个答案: