有 SwiftUI "drag enter" 手势吗？

Question

我正在尝试处理进入 SwiftUI 视图的拖动手势。但是，DragGesture 仅当事件源自视图本身时才会触发（更新、更改）。

我当然可以想到各种解决方法，但我想仔细检查是否有 easy/intended 方法来做到这一点。

我正在寻找类似于 UIKit 的东西 touchDragEnter, or JavaScript ondragenter。

Answer 1

我最终在叠加视图中拦截触摸，然后在触摸位置包含在其边界内时突出显示项目。我尝试了 onDrop 和 UIKit gestures/actions，但其中 none 没有缺点。所以我选择实施代替。

I incorporated a model object where I store the frames on every update, so highlight effect can adopt dynamically. It makes the solution animation proof, while picker also can be displayed anywhere on the screen.

import SwiftUI


class Model: ObservableObject {
    
    let coordinateSpace = "CoordinateSpace"
    
    @Published var isDragged = false
    @Published var highlightedNumber: Int? = nil
    @Published var selectedNumber: Int? = nil
    
    /// Frames for individual picker items (from their respective `GeometryReader`).
    private var framesForNumbers: [Int: CGRect] = [:]
    
    func update(frame: CGRect, for number: Int) {
        framesForNumbers[number] = frame
    }
    
    /// Updates `highlightedNumber` according drag location.
    func update(dragLocation: CGPoint) {
        
        // Lookup if any frame contains drag location.
        for (eachNumber, eachFrame) in framesForNumbers {
            if eachFrame.contains(dragLocation) {
                
                // Publish.
                self.highlightedNumber = eachNumber
                return
            }
        }
        
        // Reset otherwise.
        self.highlightedNumber = nil
    }
    
    /// Updates `highlightedNumber` and `selectedNumber` according drop location.
    func update(isDragged: Bool) {
        
        // Publish.
        self.isDragged = isDragged
        
        if isDragged == false,
           let highlightedNumber = self.highlightedNumber {
            
            // Publish.
            self.selectedNumber = highlightedNumber
            self.highlightedNumber = nil
        }
    }
}

struct ContentView: View {
    
    @StateObject var model = Model()
    
    var body: some View {
        ZStack {
            TouchesView(model: model, isDragged: $model.isDragged)
            CanvasView(number: $model.selectedNumber)
                .allowsHitTesting(false)
            PickerView(model: model, highlightedNumber: $model.highlightedNumber)
                .allowsHitTesting(false)
        }
        .ignoresSafeArea()
    }
}

/// Handles drag interactions and updates model accordingly.
struct TouchesView: View {
    
    var model: Model
    @Binding var isDragged: Bool
    
    var body: some View {
        Rectangle()
            .foregroundColor(isDragged ? .orange : .yellow)
            .coordinateSpace(name: model.coordinateSpace)
            .gesture(
                DragGesture(minimumDistance: 0)
                    .onChanged { value in
                        model.update(dragLocation: value.location)
                        model.update(isDragged: true)
                    }
                    .onEnded { state in
                        model.update(dragLocation: state.location)
                        model.update(isDragged: false)
                    }
                )
    }
}

/// Shows the selected number.
struct CanvasView: View {
    
    @Binding var number: Int?
    
    var body: some View {
        VStack {
            Text(number.string)
                .font(.system(size: 100, weight: .bold))
                .foregroundColor(.white)
                .offset(y: -50)
        }
    }
}

/// Displays a picker to select number items from.
struct PickerView: View {
    
    var model: Model
    @Binding var highlightedNumber: Int?
    
    var body: some View {
        HStack(spacing: 5) {
            PickerItemView(number: 1, model: model, highlightedNumber: $highlightedNumber)
            PickerItemView(number: 2, model: model, highlightedNumber: $highlightedNumber)
            PickerItemView(number: 3, model: model, highlightedNumber: $highlightedNumber)
        }
        .opacity(model.isDragged ? 1 : 0)
        .scaleEffect(model.isDragged ? 1 : 0.5, anchor: .top)
        .blur(radius: model.isDragged ? 0 : 10)
        .animation(.spring(response: 0.15, dampingFraction: 0.4, blendDuration: 0.5))
    }
}

/// Shows a number item (also highlights it when `highlightedNumber` matches).
struct PickerItemView: View {
    
    let number: Int
    var model: Model
    @Binding var highlightedNumber: Int?
    
    var body: some View {
        Text(String(number))
            .font(.system(size: 25, weight: .bold))
            .foregroundColor(isHighlighted ? .orange : .white)
            .frame(width: 50, height: 50)
            .background(isHighlighted ? Color.white : Color.orange)
            .cornerRadius(25)
            .overlay(
                RoundedRectangle(cornerRadius: 25)
                    .stroke(Color.white, lineWidth: 2)
            )
            .overlay(GeometryReader { geometry -> Color  in
                self.model.update(
                    frame: geometry.frame(in: .named(self.model.coordinateSpace)),
                    for: self.number
                )
                return Color.clear
            })
            .animation(.none)
    }
}

extension PickerItemView {
    
    var isHighlighted: Bool {
        self.highlightedNumber == self.number
    }
}

fileprivate extension Optional where Wrapped == Int {
    
    var string: String {
        if let number = self {
            return String(number)
        } else {
            return ""
        }
    }
}

struct PrototypeView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Only thing I dislike about this is that this method is esentially the same I did 15 years ago in a Flash app. I was hoping to something less "manual".

有 SwiftUI "drag enter" 手势吗？

Is there a SwiftUI "drag enter" gesture?

gesture

drag

swift

swiftui