ios - 如何将(可选的)完成处理程序关闭传递给 Swift 中的 transitionFromViewController？

Question

在我的应用程序的 ViewController 中，我调用了 transitionFromViewController 但在将闭包传递给 completion: 参数时总是会出现以下错误。

Type '() -> Void' does not conform to protocol 'NilLiteralConvertible'

函数调用如下:

    self.transitionFromViewController(
        self.currentVC,
        toViewController: newController,
        duration: 0.2,
        options: UIViewAnimationOptions.TransitionCrossDissolve,
        nil,
        completion: { finished in
            fromViewController.removeFromParentViewController()
            toViewController.didMoveToParentViewController(containerViewController)
            toViewController.view.frame = containerViewController.view.bounds
    })

根据代码补全，方法签名如下:

transitionFromViewController(fromViewController: UIViewController, toViewController: UIViewController, duration: NSTimeInterval, options: UIViewAnimationOptions, animations: () -> Void(), completion: ((Bool) -> Void)?)

Answer 1

您不能将 nil 传递给 animations paramere () -> Void() 声明为非可选

如果需要，传递空的闭包

self.transitionFromViewController(
        self.currentVC,
        toViewController: newController,
        duration: 0.2,
        options: UIViewAnimationOptions.TransitionCrossDissolve,
        animations: { () -> Void in

        },
        completion: { finished in
            fromViewController.removeFromParentViewController()
            toViewController.didMoveToParentViewController(containerViewController)
            toViewController.view.frame = containerViewController.view.bounds
    })