谈谈StatusBar相关的东西

  class ViewController: UIViewController {
    var style: UIStatusBarStyle = .default
    override var preferredStatusBarStyle: UIStatusBarStyle
    {
        print("无导航栏就会进来了。")
        return self.style
    }
    
    var changeBtn: UIButton!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.backgroundColor = .purple
        let btn = UIButton.init(frame: CGRect(x: 100, y: 100, width: 100, height: 50))
        btn.backgroundColor = .gray
        self.changeBtn = btn
        btn.setTitle("hit me", for: .normal)
        btn.addTarget(self, action: #selector(click), for: .touchUpInside)
        self.view.addSubview(btn)
    }

    @objc func click() {
        // 1、没有导航栏的情况
        if self.style == .lightContent {
            self.style = .default
        }else {
            self.style = .lightContent
        }
        setNeedsStatusBarAppearanceUpdate() // 在需要更新的时候调用 setNeedsStatusBarAppearanceUpdate() 方法来触发它。
    }
}

@objc func click() {
    // 2、有导航栏的情况
    if let navigationBar = self.navigationController?.navigationBar {
        if navigationBar.barStyle == .default {
            navigationBar.barStyle = .black
        } else {
            navigationBar.barStyle = .default
        }
    }
}