如何从AppDelegate获取当前可见的viewController

Question

So, I'm using the method bellow from UIApplication extension to get the top view controller:

    class func topViewController(controller: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
    if let navigationController = controller as? UINavigationController {
        return topViewController(controller: navigationController.visibleViewController)
    }
    if let tabController = controller as? UITabBarController {
        if let selected = tabController.selectedViewController {
            return topViewController(controller: selected)
        }
    }
    if let presented = controller?.presentedViewController {
        return topViewController(controller: presented)
    }
    return controller
}

But the problem is: It always returns UIViewController . But I need to check if it is MyViewController for example. How do I achieve that?

Answer 1

To use the UIViewController as MyViewController :

if let myViewController = UIApplication.topViewController() as? MyViewController { ... }

or if you just want to check that the UIViewController is of type MyViewController :

if UIApplication.topViewController() is MyViewController { ... }

Answer 2

You can do a conditional check with an if-let statement like this:

if let presented = controller?.presentedViewController as? MyViewController {
    // it is a MyViewController
}

You can also just directly check if the UIViewController is that type of class like this:

if controller?.presentedViewController is MyViewController {
    // it is a MyViewController
}

Answer 3

Try this:

if let presented = controller?.presentedViewController as? MyViewController {
    ...

Answer 4

Do conditional casting on the return value to safely check its type.

if let currentVC = UIApplication.topViewController() as? MyViewController {
   //the type of currentVC is MyViewController inside the if statement, use it as you want to
}

Your whole function implementation is flawed, if it actually worked, it would lead to infinite recursion. Once you find out the type of your current top view controller in your if statements, you are calling the same function again with the current root controller as its input value. Your function only ever exists, if it reaches either a call from a view controller, whose class is none of the ones specified in your optional bindings.

Moreover, your whole implementation doesn't do anything at the moment. You find out the type of your root view controller, but than you upcast it by returning a value of type UIViewController .

Answer 5

You can check it in following ways

class func topViewController(controller: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
        if let navigationController = controller as? UINavigationController {
            return topViewController(controller: navigationController.visibleViewController)
        }
        else if let tabController = controller as? UITabBarController {
            if let selected = tabController.selectedViewController {
                return topViewController(controller: selected)
            }
        }
        else if let presented = controller?.presentedViewController {
            return topViewController(controller: presented)
        }
        return controller
}


        // Answer 
        if let topVC = AppDelegate.topViewController() as? MyViewController {
            // Here your topVC is MyViewController
        }


        // or 
        if let topVC = AppDelegate.topViewController() {

            if topVC is MyViewController {
                // Here your topVC is MyViewController
            }
        }