UINavigationControllerDelegate的didShowViewController方法被调用了两次

Question

class ViewController: UIViewController, UINavigationControllerDelegate {

      override func viewDidLoad() {
         super.viewDidLoad()
         navigationController!.delegate = self
      }

      func navigationController(navigationController: UINavigationController, didShowViewController viewController: UIViewController, animated: Bool) {
         print("showViewController")
      }

      func navigationController(navigationController: UINavigationController, willShowViewController viewController: UIViewController, animated: Bool) {
         print("sss")
      }

      func update() {
         let vc = SecondViewController()
         navigationController!.pushViewController(vc, animated: true)
      }
}

这是我演示的第一个控制器,在控制台中:

sss
showViewController
showViewController

两次调用"didShowViewController".我不确定发生了什么

-----------------一些测试----------------------

我在控制器的这些方法中添加了一些日志:loadView,viewDidLoad,viewWillAppear,viewDidAppear,这些日志的顺序是:

loadView
viewDidLoad
viewWillAppear
will:<NaviDemo.ViewController: 0x7fe8c9533050>
<NaviDemo.ViewController: 0x7fe8c9533050>
viewDidAppear
<NaviDemo.ViewController: 0x7fe8c9533050>

Answer 1

显示UINavigationController了 a 的两个实例UIViewController

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从UINavigationControllerDelegate文档中

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在导航控制器显示视图\n控制器\xe2\x80\x99s视图和导航项属性后调用。

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不要记录“showViewController”，而是记录UIViewController实例以查看发生了什么

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func navigationController(navigationController: UINavigationController, didShowViewController viewController: UIViewController, animated: Bool) {\n     print(viewController)\n}\n

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