UIGestureRecognizer subclass-- touchesMoved自動更改狀態.changed

Question

我想創建一個UIGestureRecognizer子類，並在touchesMoved我沒有代碼，但state被設置爲.changed。

有誰知道爲什麼會發生這種情況？當我們處於.changed狀態時，我需要能夠自己決定。

如果我刪除我的touchesBegan功能並且從不移動到.began，則不會發生這種情況。

import UIKit.UIGestureRecognizerSubclass 

class MyRecognizer: UIGestureRecognizer { 

    private var refView: UIView? { 
     return self.view?.window 
    } 


    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) { 
     super.touchesBegan(touches, with: event) 

     if touches.count != 1 { 
      state = .failed 
      return 
     } 

     guard let location = touches.first?.location(in: refView) else { 
      self.state = .failed 
      return 
     } 

     state = .began 

    } 

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) { 
     // there is no code here! 
    } 

    //This is how I'm debugging state 
    override var state: UIGestureRecognizerState { 
     get { return super.state } 
     set { 
      super.state = newValue 
      print("state = \(newValue.debugDescription)") 
     } 
    } 

} 

extension UIGestureRecognizerState: CustomDebugStringConvertible { 
    public var debugDescription: String { 
     switch self { 
     case .began: return "began" 
     case .possible: return "possible" 
     case .changed: return "changed" 
     case .ended: return "ended" 
     case .cancelled: return "cancelled" 
     case .failed: return "failed" 
     } 
    } 
} 

Answer 1

您的測試方法有缺陷。我想這（這是我的測試應用程序的完整代碼）：

import UIKit 
import UIKit.UIGestureRecognizerSubclass 

class MyRecognizer: UIGestureRecognizer { 
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) { 
     super.touchesBegan(touches, with: event) 
     print(self.state.rawValue) 
    } 
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) { 
     super.touchesMoved(touches, with: event) 
     print(self.state.rawValue) 
    } 
} 

class ViewController: UIViewController { 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     let g = MyRecognizer(target: self, action: #selector(grFired)) 
     self.view.addGestureRecognizer(g) 
     // Do any additional setup after loading the view, typically from a nib. 
    } 

    @objc func grFired(_ g:UIGestureRecognizer) { 
     print("here", g.state.rawValue) 
    } 

} 

然後我一拖再拖的背景來看，到手勢識別連接。我的手勢識別器從未從possible狀態移動。

另請注意，您的期望可能不正確（「我需要能夠在我們處於.changed狀態時自行決定」）。正常和正確的行爲是，在宣佈狀態爲.began,touchesBegan後，您的touchesMoved將被調用一次，狀態爲.began，手勢識別器將自動立即前進到.changed。那就是正確;如果這是連續的手勢，那麼在moved事件應該進入而我們處於.began狀態時不會出現這種情況，而我們不會進入.changed。再次，這裏是一個測試：

import UIKit 
import UIKit.UIGestureRecognizerSubclass 

class MyRecognizer: UIGestureRecognizer { 
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) { 
     super.touchesBegan(touches, with: event) 
     if touches.count != 1 { 
      state = .failed 
      return 
     } 
     print(self.state.rawValue) 
     self.state = .began 
    } 
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) { 
     super.touchesMoved(touches, with: event) 
     print("moved", self.state.rawValue) 
    } 
} 

class ViewController: UIViewController { 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     let g = MyRecognizer(target: self, action: #selector(grFired)) 
     self.view.addGestureRecognizer(g) 
     // Do any additional setup after loading the view, typically from a nib. 
    } 

    @objc func grFired(_ g:UIGestureRecognizer) { 
     print("here", g.state.rawValue) 
    } 

}