UIBarButtonItem选择器不起作用

Question

我有一个嵌入导航控制器的MainViewController,如下所示:

在MainViewController.swift中,我以编程方式添加了两个UIBarButtonItem(左和右):

class MainViewController: UIViewController {

    let rightButton = UIBarButtonItem(title: "Right", style: .plain, target: self, action: #selector(onRightClick))
    let leftButton = UIBarButtonItem(title: "Left", style: .plain, target: self, action: #selector(onLeftClick))

    override func viewDidLoad() {
        super.viewDidLoad()
        navigationItem.rightBarButtonItem = rightButton
        navigationItem.leftBarButtonItem = leftButton
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    @objc func onRightClick() {
        print("[Main] Right Click")
    }

    @objc func onLeftClick() {
        print("[Main] Left Click")
    }
}

按钮确实显示在屏幕上,但有趣的是,选择器功能onLeftClick,onRightClick每当我按下向左或向右按​​钮时都不会被调用.我有什么办法让它有效吗？我正在使用Xcode 9.3.

Answer 1

您也可以只将lazy关键字添加到 rightButton 和 leftButton 类属性中。这样，UIBarButtonItem在类内部使用它们之前，它们不会被实例化（并且不会尝试解析动作选择器）。这样做允许您在类中的任何位置使用 barButtonItems（不仅仅是在它们声明的函数中）。

lazy var rightButton = UIBarButtonItem(title: "Right", style: .plain, target: self, action: #selector(onRightClick))
lazy var leftButton = UIBarButtonItem(title: "Left", style: .plain, target: self, action: #selector(onLeftClick))

Answer 2

尝试使用内部范围一次

override func viewDidLoad() {
    super.viewDidLoad()

    let rightButton = UIBarButtonItem(title: "Right", style: .plain, target: self, action: #selector(self.onRightLeftClick(_ :)))
    rightButton.tag = 1
    let leftButton = UIBarButtonItem(title: "Left", style: .plain, target: self, action: #selector(self.onRightLeftClick(_ :)))
    rightButton.tag = 2
    self.navigationItem.rightBarButtonItem = rightButton
    self.navigationItem.leftBarButtonItem = leftButton
}