错误：“某些视图”类型的值没有成员“中风”

Question

我关注Stanfords' CS193p Developing Apps for iOS online course。 我正在使用 Xcode 11.5。 （我没有更新，因为这是课程讲师（Paul Heagarty）正在使用的版本。）

我正在尝试执行Assignment 3 (Set Game)。目前（为了避免重复代码）我正在尝试替换这个片段：

            VStack {
                ForEach(0..<numberOfShapes) { index in
                    if self.card.shape == .diamond {
                        ZStack {
                            Diamond().fill()
                                .opacity(self.opacity)
                            Diamond().stroke(lineWidth: self.shapeEdgeLineWidth)
                        }
                    }
                    if self.card.shape == .squiggle {
                        ZStack {
                            Rectangle().fill()
                            Rectangle().stroke(lineWidth: self.shapeEdgeLineWidth)
                        }
                    }
                    if self.card.shape == .oval {
                        ZStack {
                            Ellipse().fill()
                            Ellipse().stroke(lineWidth: self.shapeEdgeLineWidth)
                        }
                    }
                }
            }

有了这个片段：

            VStack {
                ForEach(0..<numberOfShapes) { index in
                    ZStack {
                        shape(self.card.shape).opacity(self.opacity)
                        shape(self.card.shape).stroke(lineWidth: 2.5) // ERROR here: Value of type 'some View' has no member 'stroke'
                    }
                }
            }

还有这个@ViewBuilder 函数：

@ViewBuilder
func shape(_ shape: SetGameModel.Card.Shape) -> some View {
    if shape == .diamond {
        Diamond()
    } else if shape == .squiggle {
        Rectangle()
    } else {
        Ellipse()
    }
}

这里是完整的查看代码：

import SwiftUI

struct SetGameView: View {
    @ObservedObject var viewModel: SetGameViewModel
    
    var body: some View {
        Grid(viewModel.cards) { card in
                CardView(card: card).onTapGesture {
                    self.viewModel.choose(card: card)
                }
                .padding(5)
            }
        .padding()
        .foregroundColor(Color.orange)
    }
}

struct CardView: View {
    var card: SetGameModel.Card

    var numberOfShapes: Int {
        switch card.numberOfShapes {
        case .one:
            return 1
        case .two:
            return 2
        case .three:
            return 3
        }
    }
        
    var opacity: Double {
        switch card.shading {
        case .open:
            return 0.0
        case .solid: // filled
            return 1.0
        case .striped: // you can use a semi-transparent color to represent the “striped” shading.
            return 0.33
        }
    }
    
    var color: Color {
        switch card.color {
        case .green:
            return Color.green
        case .purple:
            return Color.purple
        case .red:
            return Color.red
        }
    }
    
    var body: some View {
        ZStack {
            RoundedRectangle(cornerRadius: cornerRadius).fill(Color.white)
            RoundedRectangle(cornerRadius: cornerRadius)
                .stroke(lineWidth: card.isChosen ? chosenCardEdgeLineWidth : normalCardEdgeLineWidth)
                .foregroundColor(card.isChosen ? Color.red : Color.orange)
            VStack {
                ForEach(0..<numberOfShapes) { index in
                    ZStack {
                        shape(self.card.shape).opacity(self.opacity)
                        shape(self.card.shape).stroke(lineWidth: 2.5) // ERROR here: Value of type 'some View' has no member 'stroke'
                    }
                }
            }
            .foregroundColor(self.color)
            .padding()
        }
        .aspectRatio(cardAspectRatio, contentMode: .fit)
    }
    
    // MARK: - Drawing Constants
    let cornerRadius: CGFloat = 10.0
    let chosenCardEdgeLineWidth: CGFloat = 6
    let normalCardEdgeLineWidth: CGFloat = 3
    let shapeEdgeLineWidth: CGFloat = 2.5
    let cardAspectRatio: CGSize = CGSize(width: 2, height: 3) // 2/3 aspectRatio
}

@ViewBuilder
func shape(_ shape: SetGameModel.Card.Shape) -> some View {
    if shape == .diamond {
        Diamond()
    } else if shape == .squiggle {
        Rectangle()
    } else {
        Ellipse()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        SetGameView(viewModel: SetGameViewModel())
    }
}

我有这个错误：

Value of type 'some View' has no member 'stroke'

我想不通，怎么了？我该如何解决？

请尝试以某种方式帮助我修复它，我作为初学者会理解 ????

顺便说一下，Diamond() 是我的自定义形状（如 Rectangle()）。 如果您还需要 ViewModel、Model 或其他一些文件来帮助我修复它，请告诉我:-)

Answer 1

stroke 是在 Shape 上定义的，而不是在 View 上定义的，您返回的是 Shapes，而不仅仅是 Views。需要将shape的返回类型改为some Shape。

遗憾的是@ViewBuilder 需要返回类型为some View，而不是some Shape，因此您需要删除@ViewBuilder 属性并确保您的函数从每个分支返回相同的Shape。为此，您可以实现一个类型擦除的Shape，称为AnyShape，类似于AnyView for View，并返回每个Shape 的类型擦除版本。

struct AnyShape: Shape {
    init<S: Shape>(_ wrapped: S) {
        _path = { rect in
            let path = wrapped.path(in: rect)
            return path
        }
    }

    func path(in rect: CGRect) -> Path {
        return _path(rect)
    }

    private let _path: (CGRect) -> Path
}

func shape(_ shape: SetGameModel.Card.Shape) -> some Shape {
    if shape == .diamond {
        return AnyShape(Diamond())
    } else if shape == .squiggle {
        return AnyShape(Rectangle())
    } else {
        return AnyShape(Ellipse())
    }
}