Swift 如果用户单击“后退”按钮，则快速添加操作

我使用以下代码成功检测到用户是否单击了后退按钮：

override func viewWillDisappear(animated: Bool) {
    let viewControllers: NSArray = self.navigationController?.viewControllers as! NSArray
    if viewControllers.indexOfObject(self) == NSNotFound {
        self.navigationController?.setNavigationBarHidden(true, animated: true)
    }

    super.viewWillDisappear(animated)
}

let viewControllers: [UIViewController] = self.navigationController?.viewControllers as! [UIViewController]

override func viewWillDisappear(animated: Bool) {
    if let viewControllers = navigationController?.viewControllers as? [UIViewController] {
        if let index = find(viewControllers, self) {
            navigationController?.setNavigationBarHidden(true, animated: true)
        }
    }

    viewWillDisappear(animated)
}

但我得到以下警告：

从“[AnyObject]”强制转换到不相关类型“NSArray”总是失败

---

是否有一种“更整洁”的方法来实现这一点？

基本上，问题是您试图强制转换为objective-c数组类型NSArray。Swift使用数组而不是NSArray/NSMutableArray。如果要在Swift中强制转换数组，必须指定数组中对象的类型。因此，以下代码：

override func viewWillDisappear(animated: Bool) {
    let viewControllers: NSArray = self.navigationController?.viewControllers as! NSArray
    if viewControllers.indexOfObject(self) == NSNotFound {
        self.navigationController?.setNavigationBarHidden(true, animated: true)
    }

    super.viewWillDisappear(animated)
}

let viewControllers: [UIViewController] = self.navigationController?.viewControllers as! [UIViewController]

override func viewWillDisappear(animated: Bool) {
    if let viewControllers = navigationController?.viewControllers as? [UIViewController] {
        if let index = find(viewControllers, self) {
            navigationController?.setNavigationBarHidden(true, animated: true)
        }
    }

    viewWillDisappear(animated)
}

将其强制转换为UIViewController的数组（Swift数组）。实际上，你可以把它写得更短，只需要这样：

let viewControllers = self.navigationController?.viewControllers as! [UIViewController]

---

您应该使用Swift数组-

[UIViewController]

固定问题：

override func viewWillDisappear(animated: Bool) {
        let viewControllers: [UIViewController] = self.navigationController?.viewControllers as [UIViewController]

        if let index = find(viewControllers, self)
        {
            //your object exists in that is at index

        }
        else
        {
           //your object is not in the navigation controller
           self.navigationController?.setNavigationBarHidden(true, animated: true)
        }

    super.viewWillDisappear(animated)
}

if find(viewControllers, self) == nil
{
    //your object isnt in the viewControllers array

}

如果让else，则可以使用：

override func viewWillDisappear(animated: Bool) {
        let viewControllers: [UIViewController] = self.navigationController?.viewControllers as [UIViewController]

        if let index = find(viewControllers, self)
        {
            //your object exists in that is at index

        }
        else
        {
           //your object is not in the navigation controller
           self.navigationController?.setNavigationBarHidden(true, animated: true)
        }

    super.viewWillDisappear(animated)
}

if find(viewControllers, self) == nil
{
    //your object isnt in the viewControllers array

}

---

请尝试以下代码：

override func viewWillDisappear(animated: Bool) {
    let viewControllers: NSArray = self.navigationController?.viewControllers as! NSArray
    if viewControllers.indexOfObject(self) == NSNotFound {
        self.navigationController?.setNavigationBarHidden(true, animated: true)
    }

    super.viewWillDisappear(animated)
}

let viewControllers: [UIViewController] = self.navigationController?.viewControllers as! [UIViewController]

override func viewWillDisappear(animated: Bool) {
    if let viewControllers = navigationController?.viewControllers as? [UIViewController] {
        if let index = find(viewControllers, self) {
            navigationController?.setNavigationBarHidden(true, animated: true)
        }
    }

    viewWillDisappear(animated)
}

---

在我看来，使用find（）更符合Swift。如果找到，find（）将返回元素的索引，否则返回nil。

I get

无法使用类型为“（[AnyObject]？，…”的参数列表调用“find”。

I get

[UIViewController]没有名为“indexOfObject”的成员

这将不起作用。在Swift中，navigationController.ViewController将始终包含self。有一种比查看视图中的视图控制器更简单的方法

视图将消失

。调用

IsbeingDismised

内部

视图将消失

。