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navigationController?.setViewControllers工作延迟override func viewDidAppear(，在其他情况下，它工作正常。

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    print(self.navigationController?.children)
    print(self.navigationController?.viewControllers)
    var array = self.navigationController?.children
    array!.insert(ViewController(), at: array!.count - 1)
    navigationController?.setViewControllers(array!, animated: false)
    print(self.navigationController?.viewControllers)
}

它打印：

Optional([<One.ViewController: 0x7f9a1b4021e0>, <One.TwoViewController: 0x7f9a1b40e320>])
Optional([<One.ViewController: 0x7f9a1b4021e0>, <One.TwoViewController: 0x7f9a1b40e320>])
Optional([<One.ViewController: 0x7f9a1b4021e0>, <One.TwoViewController: 0x7f9a1b40e320>])

在其他情况下，它工作正常。就像一个按钮点击。

@IBAction func back(_ sender: Any) {
    print(self.navigationController?.children)
    print(self.navigationController?.viewControllers)
    var array = self.navigationController?.children
    array!.insert(ViewController(), at: array!.count - 1)
    navigationController?.setViewControllers(array!, animated: false)
    print(self.navigationController?.viewControllers)
}


Optional([<One.ViewController: 0x7f9a1b4021e0>, <One.ViewController: 0x7f9a1b520dc0>, <One.TwoViewController: 0x7f9a1b40e320>])
Optional([<One.ViewController: 0x7f9a1b4021e0>, <One.ViewController: 0x7f9a1b520dc0>, <One.TwoViewController: 0x7f9a1b40e320>])
Optional([<One.ViewController: 0x7f9a1b4021e0>, <One.ViewController: 0x7f9a1b520dc0>, <One.ViewController: 0x7f9a1b40cd10>, <One.TwoViewController: 0x7f9a1b40e320>])

它按预期工作。

这两种方法一个接一个地起作用。

我认为navigationController?.setViewControllers可以工作override func viewDidAppear(，有点延迟。

机制是什么？

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