我目前在 Storyboard中有 3 个 UIViewController,我将它们连接到一个带有 ScrollView 的 UIPageViewController 中。但是,由于没有预加载 PageViewController 中的所有 UIViewController,我在中心 UIViewController 上初始化应用程序时遇到了一些问题。当用户首次打开应用 viewDidLoad
时,我使用 ScrollView contentOffset
显示中心 ViewController。
我已附上我在这里使用的代码:
var currentIndex = 0
var mainScrollView = UIScrollView()
lazy var ViewControllerArray: [UIViewController] = {
return [self.ViewControllerInstance(name: "RightVC"),
self.ViewControllerInstance(name: "CenterVC"),
self.ViewControllerInstance(name: "LeftVC")]
}()
private func ViewControllerInstance(name: String) -> UIViewController{
return UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: name)
}
override func viewDidLoad() {
super.viewDidLoad()
self.dataSource = self
self.delegate = self
if let CenterViewController = ViewControllerArray.first {
setViewControllers([CenterViewController] , direction: .reverse, animated: false, completion: nil)
}
}
override func viewDidAppear(_ animated: Bool) {
mainScrollView = view.subviews.filter { $0 is UIScrollView }.first as! UIScrollView
mainScrollView.delegate = self
mainScrollView.contentOffset.x = self.view.bounds.size.width * 2
}
public func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
guard let ViewControllerIndex = ViewControllerArray.index(of: viewController) else {
return nil
}
let PreviousIndex = ViewControllerIndex - 1
currentIndex = ViewControllerIndex
guard PreviousIndex >= 0 else {
return nil
}
guard ViewControllerArray.count > PreviousIndex else {
return nil
}
return ViewControllerArray[PreviousIndex]
}
public func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
guard let ViewControllerIndex = ViewControllerArray.index(of: viewController) else {
return nil
}
let NextIndex = ViewControllerIndex + 1
currentIndex = ViewControllerIndex
guard NextIndex < ViewControllerArray.count else {
return nil
}
guard ViewControllerArray.count > NextIndex else {
return nil
}
return ViewControllerArray[NextIndex]
}
// Control bounce @ DidScroll & EndDragging
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let lastPosition = scrollView.contentOffset.x
if (currentIndex == ViewControllerArray.count - 1) && (lastPosition > scrollView.frame.width) {
scrollView.contentOffset = CGPoint(x: scrollView.bounds.size.width, y: 0)
} else if currentIndex == 0 && lastPosition < scrollView.frame.width {
scrollView.contentOffset = CGPoint(x: scrollView.bounds.size.width, y: 0)
}
}
// ^^
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let lastPosition = scrollView.contentOffset.x
if (currentIndex == ViewControllerArray.count - 1) && (lastPosition > scrollView.frame.width) {
scrollView.contentOffset = CGPoint(x: scrollView.bounds.size.width, y: 0)
} else if currentIndex == 0 && lastPosition < scrollView.frame.width {
scrollView.contentOffset = CGPoint(x: scrollView.bounds.size.width, y: 0)
}
}
最佳答案
更新: 我使用变量 IntialOpen 作为系统的 bool 值来了解应用程序之前是否打开过,并且我还在公共(public)函数中添加了 If/else 语句。
public func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
guard let ViewControllerIndex = ViewControllerArray.index(of: viewController) else {
return nil
}
let PreviousIndex = ViewControllerIndex - 1
if !initialOpen {
currentIndex = ViewControllerIndex
}else{
currentIndex = ViewControllerIndex + 1
initialOpen = false
}
guard PreviousIndex >= 0 else {
return nil
}
guard ViewControllerArray.count > PreviousIndex else {
return nil
}
return ViewControllerArray[PreviousIndex]
}
public func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
guard let ViewControllerIndex = ViewControllerArray.index(of: viewController) else {
return nil
}
let NextIndex = ViewControllerIndex + 1
if !initialOpen {
currentIndex = ViewControllerIndex
}else{
currentIndex = ViewControllerIndex + 1
initialOpen = false
}
guard NextIndex < ViewControllerArray.count else {
return nil
}
guard ViewControllerArray.count > NextIndex else {
return nil
}
return ViewControllerArray[NextIndex]
}
如果这是应用程序第一次启动,则几乎可以强制它在第二页上打开。
关于ios - 在 UIPageViewControllers 中预加载所有 UIViewControllers (Swift),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/44171230/