尝试遵循this iOS开发教程。
当我到了第7步，它的代码没有改变背景色，因为它应该。
引用“步骤7添加一个名为mainColor的Color属性，该属性使用枚举的rawValue创建一个颜色。该属性初始化来自资产目录的颜色。”
下面是主题文件中的代码：

import SwiftUI

enum Theme: String {
    case bubblegum
    case buttercup
    case indigo
    case lavender
    case magenta
    case navy
    case orange
    case oxblood
    case periwinkle
    case poppy
    case purple
    case seafoam
    case sky
    case tan
    case teal
    case yellow
    
    var accentColor: Color {
            switch self {
            case .bubblegum, .buttercup, .lavender, .orange, .periwinkle, .poppy, .seafoam, .sky, .tan, .teal, .yellow: return .black
            case .indigo, .magenta, .navy, .oxblood, .purple: return .white
            }
        }
    var mainColor: Color {
        Color(rawValue) // This line not working
    }
}

如果我将代码更改为：

var mainColor: Color {
        return .red
    }

正如我所料，背景变为红色。
视图文件中的代码为：

import SwiftUI

struct CardView: View {
    let scrum: DailyScrum
    var body: some View {
        VStack(alignment: .leading) {
            Text(scrum.title)
                .font(.headline)
                .accessibilityAddTraits(.isHeader)
            Spacer()
            HStack {
                Label("\(scrum.attendees.count)", systemImage: "person.3")
                    .accessibilityLabel("\(scrum.attendees.count) attendees")
                Spacer()
                Label("\(scrum.lengthInMinutes)", systemImage: "clock")
                    .accessibilityLabel("\(scrum.lengthInMinutes) minute meeting")
                    .labelStyle(.trailingIcon)
            }
            .font(.caption)            
        }
        .padding()
        .foregroundColor(scrum.theme.accentColor)

    }
}

struct CardView_Previews: PreviewProvider {
    static var scrum = DailyScrum.sampleData[0]
    static var previews: some View {
        CardView(scrum: scrum)
            .background(scrum.theme.mainColor) // Here is were theme is called
            .previewLayout(.fixed(width: 400, height: 60))
    }
}