Swift - 运算符后的预期表达式（错误）

Question

我在下面的代码中有 2 个错误，原因相同。我该如何解决这个问题？

错误在最后两个函数的两行 return viewControllerAtIndex(index) 上都显示“运算符后的预期表达式”。

func viewControllerAtIndex(index: Int) -> WalkthroughContentViewController? {

    if index == NSNotFound || index < 0 || index >= pageHeadings.count {
        return nil
    }

    // Creating a new view controller and passing the data
    if let pageContentViewController = storyboard?.instantiateViewControllerWithIdentifier("WalkthroughContentViewController") as? WalkthroughContentViewController {

        pageContentViewController.imageFile = pageImages[index]
        pageContentViewController.heading = pageHeadings[index]
        pageContentViewController.content = pageContent[index]
        pageContentViewController.index = index

        return pageContentViewController
    }

    return nil
}


func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {

    var index = (viewController as! WalkthroughContentViewController).index
    index ++

    return viewControllerAtIndex(index)
}

func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {

    var index = (viewController as! WalkthroughContentViewController).index
    index --

    return viewControllerAtIndex(index)
}

这是来自 Simon Ng 的 Swift Book。

Answer 1

问题在于目标和后缀递增/递减运算符之间的空间。应该是index++ 和index--。