//切换为default
override func viewWillAppear(_ animated: Bool)
{
    super.viewWillAppear(animated)
    UIApplication.shared.statusBarStyle = .default
}

//切换为白色
override func viewWillDisappear(_ animated: Bool)
{
    super.viewWillDisappear(animated)
    UIApplication.shared.statusBarStyle = .lightContent
}