使用Swift 4 App（Xcode 9.X）在iOS 11中缺少第一响应者吗？

Question

I have a stripped down, code based test app (no Storyboard ), that has:

• UIWindow object
• ViewController, with its main View
• Single UIView object on top. -

To test which object is the first responder, i evaluate in tochesBegan , inside the topView as follows, but all items respond false . The Responder Chain is working because the touch is detected (both in the topView and in the main controller's view.

This is the stripped down version of the app. Given that this is not a simple view-subview hierarchy, I don't use a recursive function.

import UIKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        window = UIWindow()
        window?.rootViewController = ViewController()
        window?.makeKeyAndVisible()
        return true
    }
}
class ViewController: UIViewController {
    override func viewDidLoad() {
        let topView = View()
        self.view.addSubview(topView)
    }
}
class View: UIView {
    convenience init() {
        self.init(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        self.backgroundColor = UIColor.yellow
    }
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        let window = (UIApplication.shared).delegate?.window as? UIWindow
        let viewController = window?.rootViewController
        let mainView = viewController?.view
        print("Window?: \(window!.isFirstResponder)")
        print("View Controller?: \(viewController!.isFirstResponder)")
        print("Main View?: \(mainView!.isFirstResponder)")
        for view in (mainView?.subviews)! {
            print("Any View?: \(view.isFirstResponder)")
        }
    }
}

All evaluations return false. Am I doing something wrong here?

Regards... e

Answer 1

I believe without subclassing there are few view objects (UITextField, UITextView) that can become first responder, its better you check if UIView canBecomeFirstResponder .

If you want to achieve this functionality, such as highlighting, selecting of a UIView, you have to subclass the UIView and override the becomeFirstResponder , as following:

class CustomView: UIView {

    override var isFirstResponder: Bool {
        return true
    }

}

To test above, add following in your ViewController:

override func loadView() {
    self.view = CustomView()
}

Now check to see if our CustomView isFirstResponder:

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    print("View: \(self.view.isFirstResponder)")
}

Answer 2

I think there is no first responder from start. You can still receive events to your views.

Responder object
Mouse events and multitouch events first go to the view that is under the mouse pointer or finger; that view might or might not be the first responder.

More on responders

nextResponder
The UIResponder class does not store or set the next responder automatically, so this method returns nil by default.

More on nextResponder