Question

将我的项目转换为Swift 3语法时，我遇到了几个错误，并且能够解决除了一个之外的所有错误。

我收到的错误消息是：

"Initializer for conditional binding must have Optional type, not 'UIView'"

以下是代码（我使用Yalatis cocoapod ColorMatchTabs）：

  public func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
    self.transitionContext = transitionContext

    guard let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to),
    let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
        let containerView = transitionContext.containerView else {
        return
    }
    containerView.addSubview(toViewController.view)

    let needShow = mode == .show
    if !needShow {
        containerView.addSubview(fromViewController.view)
    }

    let animatedViewController = needShow ? toViewController : fromViewController
    let initialRect = CGRect(origin: startPoint, size: CGSize.zero)
    let initialCircleMaskPath = UIBezierPath(ovalIn: initialRect)
    let extremePoint = CGPoint(x: startPoint.x, y: animatedViewController.view.bounds.height)
    let radius = hypot(extremePoint.x, extremePoint.y)
    let finalCircleMaskPath = UIBezierPath(ovalIn: initialRect.insetBy(dx: -radius, dy: -radius))

    let maskLayer = CAShapeLayer()
    maskLayer.path = needShow ? finalCircleMaskPath.cgPath : initialCircleMaskPath.cgPath
    animatedViewController.view.layer.mask = maskLayer

    let maskLayerAnimation = CABasicAnimation(keyPath: "path")
    maskLayerAnimation.fromValue = initialCircleMaskPath.cgPath
    maskLayerAnimation.fromValue = needShow ? initialCircleMaskPath.cgPath : finalCircleMaskPath.cgPath
    maskLayerAnimation.toValue = needShow ? finalCircleMaskPath.cgPath : initialCircleMaskPath.cgPath

    maskLayerAnimation.duration = transitionDuration(using: transitionContext)
    maskLayer.add(maskLayerAnimation, forKey: "path")
}

这是失败的：

guard let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to),
    let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
        let containerView = transitionContext.containerView else {
        return
    }

此处显示错误消息：

let containerView = transitionContext.containerView else {
        return
    }

我还不太擅长快速，显然不足以解决这个错误。我很感激能得到的所有帮助！

Answer 1

transitionContext.containerView不是可选的，你不需要把它放在一个guard-let语句中，因为它总是有一个值

替换它：

guard let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to),
let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
    let containerView = transitionContext.containerView else {
    return
}

与

guard let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to),
let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from) else {
    return
}
let containerView = transitionContext.containerView

错误＆＃34;可选类型＆＃34;转换为Swift 3语法时

1 个答案: