swift - 转换为 Swift 3 语法时出现错误 "Optional type"

Question

在将我的项目转换为 Swift 3 语法时，我遇到了几个错误，但除了一个错误之外，我能够解决所有错误。

我得到的错误信息是:

“条件绑定(bind)的初始化器必须具有可选类型，而不是‘UIView’”

这是代码(我使用的是 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")
}

如果失败了:

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

错误信息出现在这里:

let containerView = transitionContext.containerView else {
        return
    }

我还不是很擅长 swift，显然还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，您不需要将它放在 guard-let 语句中，因为它总是有一个值

替换这个:

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