条件绑定的初始化器必须具有可选类型，而不是'UIView'。

Question

从 StackOverflow 的研究中，我了解到这个错误是由于尝试绑定一个不是可选项的类型引起的，但在这种情况下使用 guard ，它并没有意义。以下是我的代码：

func animateTransition(_ transitionContext: UIViewControllerContextTransitioning) {
        // Here, we perform the animations necessary for the transition

        guard let fromVC = transitionContext.viewController(forKey: UITransitionContextFromViewControllerKey) else { return }
        let fromView = fromVC.view
        guard let toVC = transitionContext.viewController(forKey: UITransitionContextToViewControllerKey) else { return }
        let toView = toVC.view
        guard let containerView = transitionContext.containerView() else { return }

        if self.presenting {
            containerView.addSubview(toView)
        }

        let animatingVC = self.presenting ? toVC : fromVC
        let animatingView = animatingVC.view
        let appearedFrame = transitionContext.finalFrame(for: animatingVC)

        var alpha: CGFloat = 1
        if self.options.contains([.AlphaChange]) {
            alpha = 0;
        }

        let initialAlpha = self.presenting ? alpha : 1
        let finalAlpha = self.presenting ? 1: alpha

        var dismissedFrame = appearedFrame
        let startRect = CGRect(origin: appearedFrame.origin, size: containerView.bounds.size)
        let offset = self.calculateStartPointOffset(startRect, options: self.options)

        if options.contains([.Dissolve]) && !self.presenting {
            dismissedFrame.size = containerView.bounds.size
            dismissedFrame.origin = CGPointZero
        } else {
            dismissedFrame = CGRect(x: offset.x, y: offset.y, width: appearedFrame.width, height: appearedFrame.height)
        }

        let initialFrame = self.presenting ? dismissedFrame : appearedFrame
        let finalFrame = self.presenting ? appearedFrame : dismissedFrame
        animatingView?.frame = initialFrame
        animatingView?.alpha = initialAlpha
        let dumpingValue = CGFloat(self.options.contains([.Interactive]) ? 1 : 0.8)

        UIView.animate(withDuration: self.transitionDuration(transitionContext), delay: 0, usingSpringWithDamping: dumpingValue, initialSpringVelocity: 0.2, options: [UIViewAnimationOptions.allowUserInteraction, UIViewAnimationOptions.beginFromCurrentState],
                                   animations:
            { () -> Void in
                animatingView?.frame = finalFrame
                animatingView?.alpha = finalAlpha
            })
        { (completed) -> Void in
                if !self.presenting {
                    fromView?.removeFromSuperview()
                    self.tDelegate?.didDissmisedPresentedViewController()
                }
                let cancelled = transitionContext.transitionWasCancelled()
                transitionContext.completeTransition(!cancelled)
        }
    }

Xcode在这一行显示了一个错误：

guard let containerView = transitionContext.containerView() else { return }

- Laurence Wingo

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显示了哪个错误？ - Ulli H

Answer 1

transitionContext.containerView()已更改为返回一个非可选类型，所以您不能将其用于像guard或if let这样的条件绑定中来初始化变量。

您应该从该行中删除guard：

let containerView = transitionContext.containerView()

- dan

---

谢谢。在从守卫条件中删除此代码后，现在它正在工作。 - Farrakh Javed

使用上面建议的代码行后，我得到了另一个错误：“无法调用非函数类型UIView; 修复：删除（）”。有什么想法吗？ - tylerSF

Answer 2

容器视图，用于呈现内容。它是呈现视图控制器和被呈现视图控制器视图的祖先视图。

这个containerView将被传递给动画控制器并返回一个非可选值。

注意：

如果let/var可选绑定只适用于右侧表达式的结果为可选项时，如果右侧表达式的结果不是可选项，则无法使用此可选绑定。这个可选绑定的重点是检查nil，仅在它非nil时使用变量。

- Ashish