ios - 如何在不在 ViewController 类中时以编程方式更改 View Controller

Question

我知道这个问题已经被问过无数次了，而且我已经看到了很多变体，包括

func performSegue(withIdentifier identifier: String, 
       sender: Any?)

以及此处提到的所有其他变体:How to call a View Controller programmatically

但是您将如何更改 ViewController 类之外的 View Controller ？例如，用户当前在 ViewController_A 上，当蓝牙设备断开连接(超出范围、信号弱等)时，CBCentral< 的 didDisconnectPeripheral 方法 被触发。在同一个方法中，我想将当前 View 更改为 ViewController_B，但是此方法不会出现在 ViewController 类中，所以方法如 performSegue 不会工作。

我在我的 AppDelegate 中实现的一个建议似乎有效(用于获取适合 iphone 屏幕尺寸的 Storyboard文件/我讨厌太多的 AutoLayout热情)

    var storyboard: UIStoryboard = self.grabStoryboard()
    display storyboard
    self.window!.rootViewController = storyboard.instantiateInitialViewController()
    self.window!.makeKeyAndVisible()

然后我尝试在我的非ViewController 类中做同样的事情

    var window: UIWindow?
    var storyboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil) //assume this is the same storyboard pulled in `AppDelegate`
    self.window!.rootViewController = storyboard.instantiateViewController(withIdentifier: "ViewController_B")
    self.window!.makeKeyAndVisible()

但是我得到一个异常抛出说 fatal error: unwrappedly found nil while unwrapping an Optional value 大概来自 window!

关于我可以做什么以及正确的设计模式是什么有什么建议吗？

Answer 1

试试这个:

protocol BTDeviceDelegate {
    func deviceDidDisconnect()
    func deviceDidConnect()
}

class YourClassWhichIsNotAViewController {

    weak var deviceDelegate: BTDeviceDelegate?


    func yourMethod() {
        deviceDelegate?.deviceDidDisconnect()
    }
}


class ViewController_A {

    var deviceManager: YourClassWhichIsNotAViewController?

    override func viewDidLoad() {

        deviceManager = YourClassWhichIsNotAViewController()
        deviceManager.delegate = self
    }
}

extension ViewController_A: BTDeviceDelegate {
    func deviceDidDisconnect() {
        DispatchQueue.main.async {
             // change the VC however you want here :)

             // updated answer with 2 examples.
             // The DispatchQueue.main.async is used here because you always want to do UI related stuff on the main queue 
             // and I am fairly certain that yourMethod is going to get called from a background queue because it is handling 
             // the status of your BT device which is usually done in the background...

             // There are numerous ways to change your current VC so the decision is up to your liking / use-case.
             // 1. If you are using a storyboard - create a segue from VC_A to VC_B with an identifier and use it in your code like this
             performSegue(withIdentifier: "YourSegueIdentifierWhichYouveSpecifiedInYourSeguesAttibutesInspector", sender: nil)

             // 2. Instantiate your VC_B from a XIB file which you've created in your project. You could think of a XIB file as a 
             // mini-storyboard made for one controller only. The nibName argument is the file's name.
             let viewControllerB = ViewControllerB(nibName: "VC_B", bundle: nil)
             // This presents the VC_B modally 
             present(viewControllerB, animated: true, completion: nil)

        }
    }

    func deviceDidConnect() {}

}

YourClassWhichIsNotAViewController 是处理蓝牙设备状态的类。在 VC_A 内部启动它并适本地响应委托(delegate)方法。这应该是您正在寻找的设计模式。