ios - 如何防止 UIPageViewController 的 setViewControllers 方法崩溃？

Question

我第一次尝试让 UIPageViewController 工作，但每当我尝试设置它的 View Controller 时，我似乎都遇到了麻烦。

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.
    let leftViewController = storyboard?.instantiateViewControllerWithIdentifier("LeftViewController")
    let rightViewController = storyboard?.instantiateViewControllerWithIdentifier("RightViewController")

    let viewControllerArray: [UIViewController] = [leftViewController!, rightViewController!]

    self.setViewControllers(viewControllerArray, direction: .Forward, animated: true, completion: nil)
}

每次我到达 setViewControllers() 方法时，应用程序都会在 AppDelegate 文件中崩溃，并显示以下错误日志:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', 
reason: 'The number of view controllers provided (2) doesn't match the number 
required (1) for the requested transition

23  UIKit                               0x0000000103a06610 UIApplicationMain + 171
24  PageViewTesting                     0x000000010300649d main + 109
25  libdyld.dylib                       0x0000000105a3292d start + 1
26  ???                                 0x0000000000000001 0x0 + 1)
libc++abi.dylib: terminating with uncaught exception of type NSException

目前我的 Storyboard中有一个 UIPageViewController 和两个 UIViewControllers。我已经仔细检查过它们的 ID 对于 instantiateViewControllerWithIdentifier() 方法也是正确的。

关于我收到此错误的原因有什么想法吗？

Answer 1

来自 UIPageViewController 的类引用:

// setViewControllers:direction:animated:completion:
func setViewControllers(_ viewControllers: [UIViewController]?,
          direction direction: UIPageViewControllerNavigationDirection,
           animated animated: Bool,
         completion completion: ((Bool) -> Void)?)

The view controllers passed to this method are those that will be visible after the animation has completed. Use a data source to provide additional view controllers to which users navigate.

对于单 View Controller View 模式，代码中使用的方法.setViewControllers 只需要一个 View Controller (但是，在数组形式上)。参数采用数组 [UIViewController] 有点令人困惑，但这是为了在使用 spine(中间) View 时使用 PageViewController 的 doubleSided 属性。

When defining a page view controller interface, you can provide the content view controllers one at a time (or two at a time, depending upon the spine position and double-sided state)

...

UIPageViewControllerSpineLocationMid

Spine in the middle or the screen.

Two view controllers are displayed at a time.

您打算使用书脊中 View 吗？在这种情况下，您可以发送两个 View Controller ，否则，您应该只发送一个并使用数据源添加其他 View Controller 。