如何在 SwiftUI 中实现触发 switch case 的左或右 DragGesture()？

Question

我在视图中创建了一个 DragGesture，无论用户向左滑动还是向右滑动，它都应该选择一个 @State(Bool)。

问题是只检测到向右滑动。

如何使用 .gesture() 来捕捉用户是在他的屏幕上向左还是向右滑动？

import SwiftUI

struct SwiftUIView: View {

  //MARK: Value to change on swipe gesture
  @State var swipeRight: Bool

  var body: some View {
    VStack {
      //MARK: Value displayed after user swiped
      Text($swipeRight ? "Right" : "Left")
    }
    .gesture(
      DragGesture()
        .onChanged { (value) in
          //MARK: What is it missing here?
          switch value.location.x {
          case ...(-0.5):
            self.swipeRight = false
            print("Swipe Left return false")
          case 0.5...:
            self.swipeRight = true
            print("Swipe Right return true")
          default: ()
          }
    })
}

Answer 1

斯威夫特 5，iOS 13

[Mojtaba Hosseini][1] 提出的改进版本在这里。

[1]： https : //stackoverflow.com/users/5623035/mojtaba-hosseini 。 将枚举和函数放在 ContentView 的主体之前。

enum SwipeHVDirection: String {
    case left, right, up, down, none
}

func detectDirection(value: DragGesture.Value) -> SwipeHVDirection {
if value.startLocation.x < value.location.x - 24 {
            return .left
          }
          if value.startLocation.x > value.location.x + 24 {
            return .right
          }
          if value.startLocation.y < value.location.y - 24 {
            return .down
          }
          if value.startLocation.y > value.location.y + 24 {
            return .up
          }
  return .none
  }

...

在 DragGesture 中调用它。 在 onEnded 上调用它以阻止它多次触发。

.gesture(DragGesture()
        .onEnded { value in
        print("value ",value.translation.width)
          let direction = self.detectDirection(value: value)
          if direction == .left {
            // your code here
          }  
        }
      )

显然你需要/可以根据需要添加其他方向......

Answer 2

您应该比较旧位置和新位置：

if value.startLocation.x > value.location.x {
    print("Swipe Left")
} else {
    print("Swipe Right")
}

因此，您的代码的重构版本将是：

struct ContentView: View {
    enum SwipeHorizontalDirection: String {
        case left, right, none
    }

    @State var swipeHorizontalDirection: SwipeHorizontalDirection = .none { didSet { print(swipeHorizontalDirection) } }

    var body: some View {
        VStack {
            Text(swipeHorizontalDirection.rawValue)
        }
        .gesture(
            DragGesture()
                .onChanged {
                    if $0.startLocation.x > $0.location.x {
                        self.swipeHorizontalDirection = .left
                    } else if $0.startLocation.x == $0.location.x {
                        self.swipeHorizontalDirection = .none
                    } else {
                        self.swipeHorizontalDirection = .right
                    }
        })
    }
}

Answer 3

我认为上面的方向是颠倒的？ 或者我误解了左右滑动。 无论如何，这是使用视图修饰符的进一步改进。 你可以在 .onSwipe { direction in ... } 到你的观点。

struct SwipeModifier: ViewModifier {
    let action: ((UISwipeGestureRecognizer.Direction) -> Void)?

    init(perform action: ((UISwipeGestureRecognizer.Direction) -> Void)? = nil) {
        self.action = action
    }
        
    func body(content: Content) -> some View {
        content
            .gesture(DragGesture(minimumDistance: 24.0, coordinateSpace: .local)
                        .onEnded { value in
                            guard let action = action else {
                                return
                            }
                            if value.startLocation.x > value.location.x {
                                action(.left)
                            } else if value.startLocation.x < value.location.x {
                                action(.right)
                            } else if value.startLocation.y > value.location.y {
                                action(.down)
                            } else if value.startLocation.y < value.location.y {
                                action(.up)
                            }
                        })
    }
}

extension View {
    public func onSwipe(perform action: ((UISwipeGestureRecognizer.Direction) -> Void)? = nil) -> some View {
        return self.modifier(SwipeModifier(perform: action))
    }
}