直到视图出现时才会设置UIButton标题

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    yourButton.setTitle("按钮标题", for: .normal)
}

yourButton.addObserver(self, forKeyPath: "hidden", options: .new, context: nil)

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if keyPath == "hidden" {
        if let button = object as? UIButton, button == yourButton, let isHidden = change?[.newKey] as? Bool, !isHidden {
            yourButton.setTitle("按钮标题", for: .normal)
        }
    }
}

class YourViewController: UIViewController {
    var updateButtonTitle: (() -> Void)?
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        updateButtonTitle?()
    }
}

// 在使用该视图控制器的地方
let viewController = YourViewController()
viewController.updateButtonTitle = {
    yourButton.setTitle("按钮标题", for: .normal)
}