在 ZStack 中时 SwiftUI 不居中

Question

我正在尝试将一个 View 放在一起，该 View 由顶部标题 View 、底部内容 View 和位于顶部的 View 组成，该 View 以分割两个 View 的线为中心。我发现我需要 ZStack 中的对齐指南来定位中间 View ，但我无法让下方内容 View 中的项目无间隙地居中。

这段代码:

extension VerticalAlignment {
    struct ButtonMid: AlignmentID {
        static func defaultValue(in context: ViewDimensions) -> CGFloat {
            return context[.bottom]
        }
    }
    static let buttonMid = VerticalAlignment(ButtonMid.self)
}

struct ContentView: View {
    var body: some View {
        VStack {
            ZStack(alignment: Alignment(horizontal: .center, vertical: .buttonMid)) {
                HeaderView()
                    .frame(maxWidth: .infinity, minHeight: 200, idealHeight: 200, maxHeight: 200, alignment: .topLeading)
                
//                BodyView()
//                    .alignmentGuide(.buttonMid, computeValue: { dimension in
//                        return dimension[VerticalAlignment.top]
//                    })
                
                Color.red
                    .frame(width: 380, height: 50, alignment: /*@START_MENU_TOKEN@*/.center/*@END_MENU_TOKEN@*/)
                    .alignmentGuide(.buttonMid, computeValue: { dimension in
                        return dimension[VerticalAlignment.center]
                    })
            }
            
            BodyView()
        }
        .edgesIgnoringSafeArea(.top)
    }
}

struct HeaderView: View {
    var body: some View {
        Color.green
    }
}

struct BodyView: View {
    var body: some View {
        VStack {
            Spacer()
            HStack {
                Spacer()
                BodyContent()
                Spacer()
            }
            Spacer()
        }
        .background(Color.blue)
    }
}

struct BodyContent: View {
    var body: some View {
        VStack {
            Text("Line 1")
            Text("Line 2")
            Text("Line 3")
        }
    }
}

给你这个:

按照我想要的方式将较低的内容居中，但是它在上下 View 之间留下了间隙。如果我取消注释 ZStack 中的 BodyView 代码并在 VStack 中将其注释掉，如下所示:

struct ContentView: View {
    var body: some View {
        VStack {
            ZStack(alignment: Alignment(horizontal: .center, vertical: .buttonMid)) {
                HeaderView()
                    .frame(maxWidth: .infinity, minHeight: 200, idealHeight: 200, maxHeight: 200, alignment: .topLeading)
                
                BodyView()
                    .alignmentGuide(.buttonMid, computeValue: { dimension in
                        return dimension[VerticalAlignment.top]
                    })
                
                Color.red
                    .frame(width: 380, height: 50, alignment: /*@START_MENU_TOKEN@*/.center/*@END_MENU_TOKEN@*/)
                    .alignmentGuide(.buttonMid, computeValue: { dimension in
                        return dimension[VerticalAlignment.center]
                    })
            }
            
//            BodyView()
        }
        .edgesIgnoringSafeArea(.top)
    }
}

给你:

使内容不居中。我怎样才能让它居中？我尝试将其放入 GeometryReader 中，结果相同。

Answer 1

您不需要自定义 VerticalAlignment。相反，您可以将中间 View 作为叠加层并将其与底部 View 的顶部边框对齐:

struct ContentView: View {
    var body: some View {
        VStack(spacing: 0) {
            HeaderView()
                .frame(height: 200)
            BodyView()
                .overlay(
                    Color.red
                        .frame(width: 380, height: 50)
                        .alignmentGuide(.top) { $0[VerticalAlignment.center] },
                    alignment: .top
                )
        }
        .edgesIgnoringSafeArea(.top)
    }
}