UIPageViewControllers UIPageControl在转换过程中出现故障

Question

我有三个控制器，它们将通过UIPageViewController显示。它工作得很好，但UIPageControl在转换过程中确实会闪烁。我在这里错过/没看到什么？

我将向您展示我的UIPageViewController实现、ViewController实现以及我用来推送它的代码。谢谢您的时间！

我创建UIPageViewController的代码及其包含的控制器：

let blueVC = EmptyViewController()
blueVC.view.backgroundColor = UIColor.blue
blueVC.title = "blauer Controller"
let greenVC = EmptyViewController()
greenVC.view.backgroundColor = UIColor.green
greenVC.title = "grüner Controller"
let redVC = EmptyViewController()
redVC.view.backgroundColor = UIColor.red
redVC.title = "roter Controller"
let subViewControllers = [blueVC, greenVC, redVC]
let pageViewController = DemoPageViewController(withControllers: subViewControllers)
self.navigationController?.pushViewController(pageViewController, animated: true)

PageViewController:

import UIKit
class DemoPageViewController: UIPageViewController {
private var myViewControllers = [UIViewController]()
public init(withControllers controllers: [UIViewController]) {
self.myViewControllers = controllers
super.init(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
self.setViewControllers([controllers.first!], direction: .forward, animated: true, completion: nil)
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.view.backgroundColor = UIColor.clear
}
override func viewDidLoad() {
super.viewDidLoad()
self.dataSource = self
// Do any additional setup after loading the view.
}
}
extension DemoPageViewController: UIPageViewControllerDataSource {
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
guard let viewControllerIndex = self.myViewControllers.index(of: viewController) else {
return nil
}
let previousIndex = viewControllerIndex - 1
guard previousIndex >= 0 else {
return self.myViewControllers.last
}
guard self.myViewControllers.count > previousIndex else {
return nil
}
return self.myViewControllers[previousIndex]
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
guard let viewControllerIndex = self.myViewControllers.index(of: viewController) else {
return nil
}
let nextIndex = viewControllerIndex + 1
guard nextIndex < self.myViewControllers.count else {
return self.myViewControllers.first
}
guard self.myViewControllers.count > nextIndex else {
return nil
}
return self.myViewControllers[nextIndex]
}
func presentationCount(for pageViewController: UIPageViewController) -> Int {
return self.myViewControllers.count
}
func presentationIndex(for pageViewController: UIPageViewController) -> Int {
return 0
}
}

EmptyViewControllers:的附加实现

import Foundation
import PureLayout
import UIKit
class EmptyViewController: UIViewController {
var didSetupConstraints = false
override func loadView() {
self.view = UIView()
self.view.backgroundColor = UIColor.white
self.view.setNeedsUpdateConstraints() // bootstrap Auto Layout
}
override func viewDidLoad() {
super.viewDidLoad()
print("(#function) in (#file)")
// Do any additional setup after loading the view, typically from a nib.
}
override func updateViewConstraints() {
// Check a flag didSetupConstraints before creating constraints, because this method may be called multiple times, and we
// only want to create these constraints once. Without this check, the same constraints could be added multiple times,
// which can hurt performance and cause other issues. See Demo 7 (Animation) for an example of code that runs every time.
if !self.didSetupConstraints {
// set Constraints here
self.didSetupConstraints = true
}
super.updateViewConstraints()
}
}

Answer 1

我刚刚找到原因。这种闪烁是由背景中的ViewController引起的，因为背景是清晰的。将背景设置为黑色确实有所帮助。