状态栏

1. 配置项(info.plist)

    <key>UIViewControllerBasedStatusBarAppearance</key>
    <true/>

Apps default to using the new view controller-based status bar >management system. To opt out of this, add a value of NO for the UIViewControllerBasedStatusBarAppearance key to your Info.plist.

UIViewControllerBasedStatusBarAppearance默认是true
当UIViewControllerBasedStatusBarAppearance == true的时候，ViewController和NavigationController才能对StatueBar的前景样式进行更改。
当UIViewControllerBasedStatusBarAppearance == false的时候，需要Application级别对其进行修改才能生效。

Applicaiton级别的两种修改方式

• info.plist（当然这里可以直接在xcode->target->deployinfo->statue bar style中直接设置）

    <key>UIStatusBarStyle</key>
    <string>UIStatusBarStyleLightContent</string>

• UIAplication

//9以后被遗弃了
application.setStatusBarStyle(.default, animated: false)

2. ViewController中对StatueBar进行修改
   在ViewController中重写相应的方法并调用需要更新

    override var preferredStatusBarStyle: UIStatusBarStyle{
        return .lightContent
    }
    
    override var prefersStatusBarHidden: Bool{
        return true
    }
    override func viewDidLoad() {
        super.viewDidLoad()
        //通知系统咱需要更新状态栏
        self.setNeedsStatusBarAppearanceUpdate()
    }

完成了上一步后，重写的两个方法没有导航的情况下是可以的。可是一但加了导航NavigationController，self.setNeedsStatusBarAppearanceUpdate()之后，系统会调用导航控制器中的preferredStatusBarStyle和prefersStatusBarHidden。所以，还需要继承导航控制器并重写相应的方法：

class BearNavigationViewController: UINavigationController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    //就是这两个方法
    override var childViewControllerForStatusBarStyle: UIViewController?{
        return self.topViewController
    }
    override var childViewControllerForStatusBarHidden: UIViewController?{
        return self.topViewController
    }
}