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，每当我按下向左或向右按​​钮时，选择器函数onLeftClick和onRightClick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

尝试使用内部范围

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
}

将操作处理为

func onRightLeftClick(_ sender: UIBarButtonItem){
    if sender.tag == 1{
        // rightButton action
    }else{
        // leftButton action
    }
}

Answer 2

您也可以只将lazy关键字添加到rightButton和leftButton类属性中。这样，UIBarButtonItem不会实例化（并且动作选择器也不会尝试解析），除非它们在类中使用。通过这种方式，您可以在类中的任何位置使用barButtonItems（不仅在声明它们的函数中）。

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))