swift - 在 Swift 中以编程方式更改导航栏项目

Question

所以我正在尝试更改 viewWillAppear 中的左侧导航栏按钮项目(该项目需要来回更改，因此 viewDidLoad 将不起作用)。我在 viewWillAppear 中有以下代码:

        // There is a diff 'left bar button item' defined in storyboard. I'm trying to replace it with this new one
        var refreshButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.Refresh, target: self, action: {})
        self.navigationController.navigationItem.leftBarButtonItem = refreshButton
        // title and color of nav bar can be successfully changed
        self.navigationController.navigationBar.barTintColor = UIColor.greenColor()
        self.title = "Search result"

我使用调试器来确保每一行都被执行。但是“leftBarButtonItem”没有更新。然而，导航栏的内容已成功更新。我现在没 Action 了。想法？谢谢!

Answer 1

下面的代码应该可以工作:

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let refreshButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.Refresh, target: self, action: "buttonMethod")
        navigationItem.leftBarButtonItem = refreshButton

        navigationController?.navigationBar.barTintColor = UIColor.greenColor()
        title = "Search result"
    }

    func buttonMethod() {
        print("Perform action")
    }

}

如果确实需要在viewWillAppear:中执行，代码如下:

import UIKit

class ViewController: UIViewController {

    var isLoaded = false

    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)

        if !isLoaded {
            let refreshButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.Refresh, target: self, action: "buttonMethod")
            navigationItem.leftBarButtonItem = refreshButton
            isLoaded = true

            navigationController?.navigationBar.barTintColor = UIColor.greenColor()
            title = "Search result"
        }
    }

    func buttonMethod() {
        print("Perform action")
    }

}

您可以通过 this previous question 了解有关 navigationItem 属性的更多信息.