遇到此断言的直接方法是为UIPageController 使用滚动转换样式定义的循环源。
当源包含两页时，每一页是前一页，后一页是另一页。如果您滑动包含两页的UIPageController，然后尝试将源设置为三页，您将得到上述断言，并保证假设UIPageControllerDataSource before/after 方法允许在两页的情况下循环转换。
使用UIPageController带滚动过渡的无崩溃主要规则：
1) 在调用setViewControllers 方法之前设置dataSource
2) 使用不带动画的setViewControllers 方法(animated: false)
3) 将 dataSource 设置为 nil 用于单页模式
4) 两页模式不允许循环
所有这些建议一起使UIPageController 绝对稳定。
import UIKit
/// Convenient subclass of UIPageViewController
@objc class AMPageViewController: UIPageViewController {
/// Turn on/off PageControl at the bottom
@objc var showPageControl: Bool = true
/// Array of all viewControllers
@objc var source: [UIViewController]? {
didSet {
let count = source?.count ?? 0
if count > 0 {
dataSource = count > 1 ? self : nil
}
else {
dataSource = nil
delegate = nil
}
}
}
/// Index of the current viewController from source
@objc var pageIndex: Int {
get {
var currentPageIndex: Int = 0
if let vc = viewControllers?.first, let source = source, let pageIndex = source.index(of: vc) {
currentPageIndex = pageIndex
}
return currentPageIndex
}
set {
guard newValue >= 0, let source = source, newValue < source.count else { return }
let vc = source[newValue]
let direction: UIPageViewControllerNavigationDirection = newValue < pageIndex ? .reverse : .forward
setViewController(vc, direction: direction)
}
}
override weak var delegate: UIPageViewControllerDelegate? {
get { return super.delegate }
set {
if source?.count ?? 0 > 0 {
super.delegate = newValue
}
else {
super.delegate = nil
}
}
}
/// Initializer in scroll-mode with interPageSpacing
@objc init(navigationOrientation: UIPageViewControllerNavigationOrientation = .horizontal, interPageSpacing: Int = 0) {
let options = (interPageSpacing > 0) ? [UIPageViewControllerOptionInterPageSpacingKey : 5] : nil
super.init(transitionStyle: .scroll, navigationOrientation: navigationOrientation, options: options)
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
/// Set viewcontroller by index from source
@objc func setPageIndex(_ index: Int, completion: ((Bool) -> Void)? = nil) {
guard index > 0, let source = source, index < source.count else { return }
let vc = source[index]
let direction: UIPageViewControllerNavigationDirection = index < pageIndex ? .reverse : .forward
setViewController(vc, direction: direction, completion: completion)
}
private func setViewController(_ viewController: UIViewController, direction: UIPageViewControllerNavigationDirection = .forward, completion: ((Bool) -> Void)? = nil) {
super.setViewControllers([viewController], direction: direction, animated: false, completion: completion)
}
}
extension FFPageViewController: UIPageViewControllerDataSource {
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
guard let source = source, let index = source.index(of: viewController) else { return nil }
let count = source.count
if count == 2, index == 0 {
return nil
}
let prevIndex = (index - 1) < 0 ? count - 1 : index - 1
let pageContentViewController: UIViewController = source[prevIndex]
return pageContentViewController
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
guard let source = source, let index = source.index(of: viewController) else { return nil }
let count = source.count
if count == 2, index == 1 {
return nil
}
let nextIndex = (index + 1) >= count ? 0 : index + 1
let pageContentViewController = source[nextIndex]
return pageContentViewController
}
func presentationCount(for pageViewController: UIPageViewController) -> Int {
return showPageControl ? (source?.count ?? 0) : 0
}
func presentationIndex(for pageViewController: UIPageViewController) -> Int {
guard showPageControl else { return 0 }
return pageIndex
}
}
可以在GitHub project找到整体实现和使用示例。