如何在不在 ViewController 类中时以编程方式更改视图控制器

Question

我知道这个问题已经被问过无数次了，而且我看到了很多变化，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 类之外的视图控制器？例如，用户当前在ViewController_A 上，当蓝牙设备已断开连接（超出范围、信号弱等）时，CBCentral 的didDisconnectPeripheral 方法被触发。在同样的方法中，我想将当前视图更改为ViewController_B，但是这种方法不会出现在ViewController 类中，所以像performSegue 这样的方法将不起作用。

我在AppDelegate 中实施的一个建议似乎可行（用于获取适合 iphone 屏幕尺寸的故事板文件/我非常讨厌AutoLayout）

    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: unexpectedly found nil while unwrapping an Optional value大概来自window!

对我能做什么以及正确的设计模式有什么建议？

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 内部启动它并适当地响应委托方法。这应该是您正在寻找的设计模式。

Answer 2

我更喜欢 dvdblk 的解决方案，但我不确定如何实现 DispatchQueue.main.async（我还是 Swift 的新手）。所以这是我的迂回，低效的解决方案：

在我的didDisconnectPeripheral 中，我有一个singleton 和一个boolean attribute，它表示只要有断开连接。

在我的viewdidload 或ViewController 中，我将运行一个scheduledTimer 函数，该函数将定期检查boolean attribute 的状态。随后，在我的viewWillDisappear 中，我使计时器无效。