SwiftUI:多点触控手势/多个手势

Question

在SwiftUI中有没有一种方法可以一次跟踪多个手势？我希望我的一个主视图能够同时跟踪多个手指的拖动。

ZStack {
    Color.black
      .edgesIgnoringSafeArea(.all)
      .gesture(DragGesture(minimumDistance: 0)
               .onChanged { (value) in
                 //some logic
               }.onEnded { (value) in
                  //more logic         
               })
       //other code
}

我有这个代码，但是我一次只能处理一个拖动手势。如果一个手指正在拖动，然后我尝试添加另一个手指，则第一个手指停止。

我正在尝试实现多个手指同时出现在屏幕上的效果。每个手指同时拖动一个圆(每个手指后面跟着一个圆)。

我在苹果的文档中看到了simultaneous gestures，但这指的是让一个手势触发多个块。

Answer 1

使用UIViewRepresentable的解决方案(How to detect a tap gesture location in SwiftUI?)可以工作。尽管它不是纯粹的swiftUI解决方案(我一直在寻找纯粹的swiftUI解决方案，但是找不到一个，并且很有兴趣看到一个)。我已经将代码更新为下面的代码，您需要更改numberOfTouchPoints = 5。然后使用回调将值放入视图中。

struct TapView: UIViewRepresentable {
    var tappedCallback: (() -> Void)

    func makeUIView(context: UIViewRepresentableContext<TapView>) -> TapView.UIViewType {
        let v = UIView(frame: .zero)
        let gesture = NFingerGestureRecognizer(target: context.coordinator,
                                                       action: #selector(Coordinator.tapped))
        v.addGestureRecognizer(gesture)
        return v
    }

    class Coordinator: NSObject {
        var tappedCallback: (() -> Void)

        init(tappedCallback: @escaping (() -> Void)) {
            self.tappedCallback = tappedCallback
        }

        @objc func tapped(gesture:NFingerGestureRecognizer) {
            for i in 0..<gesture.numberOfTouches{
                print(gesture.location(ofTouch: i, in: gesture.view))
            }
            self.tappedCallback()
        }
    }

    func makeCoordinator() -> TapView.Coordinator {
        return Coordinator(tappedCallback:self.tappedCallback)
    }

    func updateUIView(_ uiView: UIView,
                      context: UIViewRepresentableContext<TapView>) {
    }
}

class NFingerGestureRecognizer: UIGestureRecognizer {
    var numberOfTouchPoints: Int = 2
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        if self.state == .possible {
            if (self.numberOfTouches == numberOfTouchPoints){ // we have a two finger interaction starting
                self.state = .began
                print("two finger drag - Start")
            }
        } else {        // check to see if there are more touchs
            if (self.numberOfTouches > numberOfTouchPoints){ // we have a two finger interaction starting
                self.state = .failed
                print("two finger drag - failed")
            }
        }
        //printInternalTouches()
    }
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        if (self.state != .possible){
            self.state = .changed        // we are looking for two finger interaction
            //printInternalTouches()
            print("changed")
        }
    }
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        self.state = .failed
        //printInternalTouches()
        print("ended")
    }

    private func printInternalTouches(){
        // now print the internal touchUI elements - should be the better solution
        print("Internal Locations")
        for i in 0..<self.numberOfTouches{
            print(self.location(ofTouch: i, in: self.view))
        }
    }
}

Answer 2

我将Paul的答案与苹果的过时示例相结合，创建了一种检测任意数量触摸的方法。

import Foundation
import UIKit

class NFingerGestureRecognizer: UIGestureRecognizer {

    var tappedCallback: (UITouch, CGPoint?) -> Void

    var touchViews = [UITouch:CGPoint]()

    init(target: Any?, tappedCallback: @escaping (UITouch, CGPoint?) -> ()) {
        self.tappedCallback = tappedCallback
        super.init(target: target, action: nil)
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        for touch in touches {
            let location = touch.location(in: touch.view)
            print("Start: (\(location.x)/\(location.y))")
            touchViews[touch] = location
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        for touch in touches {
            let oldLocation = touchViews[touch]!
            let newLocation = touch.location(in: touch.view)
            touchViews[touch] = newLocation
            print("Move: (\(oldLocation.x)/\(oldLocation.y)) -> (\(newLocation.x)/\(newLocation.y))")
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        for touch in touches {
            let oldLocation = touchViews[touch]!
            touchViews.removeValue(forKey: touch)
            print("End: (\(oldLocation.x)/\(oldLocation.y))")
        }
    }

}

更新：

您需要将其包装到UIViewRepresentable中以将其用作SwiftUI组件：

import Foundation
import SwiftUI

struct TapView: UIViewRepresentable {

    var tappedCallback: (UITouch, CGPoint?) -> Void

    func makeUIView(context: UIViewRepresentableContext<TapView>) -> TapView.UIViewType {
        let v = UIView(frame: .zero)
        let gesture = NFingerGestureRecognizer(target: context.coordinator, tappedCallback: tappedCallback)
        v.addGestureRecognizer(gesture)
        return v
    }
    
    func updateUIView(_ uiView: UIView, context: UIViewRepresentableContext<TapView>) {
        // empty
    }

}

更新2：

下面是一个如何在SwiftUI中使用TapView的小示例：

var body: some View {
    guard let img = UIImage(named: "background.png") else {
        fatalError("Unable to load image")
    }
    return GeometryReader { geometry in
        ZStack {
            Image(uiImage: img)
                    .resizable()
                    .aspectRatio(geometry.size, contentMode: .fill)
                    .edgesIgnoringSafeArea(.all)


            TapView { touch, optLocation in
                // touch can be used as a dictionary key.
                // optLocation is nil when the touch ends.
            }
        }
    }
}