获取 UINavigationController 的进度向后滑动

Question

我有两个viewControllers，它们都是UINavigationController 的一部分。 从View1 我可以点击UITableViewCell 并转到View2，从View2 我可以滑动回到View1。

我想知道如何才能获得此过渡的进度，但我未能成功：

override func viewDidAppear(_ animated: Bool) {
    navigationController?.interactivePopGestureRecognizer?.addTarget(self, action: #selector(going))
}
@objc func going(){
        print(self.transitionCoordinator?.percentComplete)
}

going 函数在转换过程中被多次调用，但 print 语句只打印 nil。我尝试使用其他视图控制器（View1 和父导航控制器）无济于事。

提前致谢

Answer 1

这似乎可行：

    private var currentTransitionCoordinator: UIViewControllerTransitionCoordinator?

    @objc private func onGesture(sender: UIGestureRecognizer) {
        switch sender.state {
        case .began, .changed:
            if let ct = navigationController?.transitionCoordinator {
                currentTransitionCoordinator = ct
            }
        case .cancelled, .ended:
            currentTransitionCoordinator = nil
        case .possible, .failed:
            break
        }

        if let currentTransitionCoordinator = currentTransitionCoordinator {
            print(currentTransitionCoordinator.percentComplete)
        }

    }

放手之后就没有任何进展了。我尝试将协调器保留更长时间并在计时器上打印值，但我什至崩溃了。

无论如何，我认为这就是您所需要的。

测试场景：

创建一个新项目并导航到主情节提要。添加导航控制器并将其根视图控制器设置为故事板中的ViewController（删除自动生成的根）。

然后转到 ViewController.swift 并用以下内容覆盖它：

import UIKit

class ViewController: UIViewController {

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        if let controller = navigationController, controller.viewControllers.count <= 1 { // Present it first time only
            view.backgroundColor = UIColor.green
            let newController = ViewController()
            newController.view.backgroundColor = UIColor.red
            navigationController?.interactivePopGestureRecognizer?.addTarget(newController, action: #selector(onGesture))
            navigationController?.pushViewController(newController, animated: true)
        }
    }

    private var currentTransitionCoordinator: UIViewControllerTransitionCoordinator?

    @objc private func onGesture(sender: UIGestureRecognizer) {
        switch sender.state {
        case .began, .changed:
            if let ct = navigationController?.transitionCoordinator {
                currentTransitionCoordinator = ct
            }
        case .cancelled, .ended:
            currentTransitionCoordinator = nil
        case .possible, .failed:
            break
        }

        if let currentTransitionCoordinator = currentTransitionCoordinator {
            print(currentTransitionCoordinator.percentComplete)
        }

    }

}

当您拖动手指，关闭当前推送的视图控制器时，您应该能够看到打印出来的百分比。