无法从 SwiftUI 中的自定义结构体数据更改预览的背景颜色

Question

我正在按照 本教程学习 Swift 和 SwiftUI。预览的背景颜色未按预期更改。

我的代码

Theme.swift

：

import SwiftUI

enum Theme: String {
    // ...others
    case yellow

    var accentColor: Color {
        switch self {
        case /* ...others */ .yellow: return .black // <-- Declare the yellow key for accent color
        case .indigo, .magenta, .navy, .oxblood, .purple: return .white
        }
    }
    var mainColor: Color {
        Color(rawValue)
    }
}

DailyScrum.swift

：

import Foundation

struct DailyScrum {
    var title: String
    var attendees: [String]
    var lengthInMinutes: Int
    var theme: Theme
}

extension DailyScrum {
    static let sampleData: [DailyScrum] =
    [
        DailyScrum(title: "Design",
                   attendees: ["Cathy", "Daisy", "Simon", "Jonathan"],
                   lengthInMinutes: 10,
                   theme: .yellow), // <-- assign yellow to the first item's theme which referred to the `Theme.swift`
        // others
    ]
}

CardView.swift

：

import SwiftUI


struct CardView: View {
    let scrum: DailyScrum
    var body: some View {
        Text("Hello, World!")
    }
}


struct CardView_Previews: PreviewProvider {
    static var scrum = DailyScrum.sampleData[0] // <-- get first item
    static var previews: some View {
        CardView(scrum: scrum)
            .background(scrum.theme.mainColor) // <-- get the mainColor of the first item
    }
}

我在预览中收到的内容： ，背景黄色应该会出现，但没有。

我尝试将

scrum.theme.mainColor

更改为

.yellow

或

scrum.theme.accentColor

，它有效。我不确定这里出了什么问题。

我的Xcode版本是15，Swift是5.9.2。

Answer 1

您可以这样调试视图：

struct CardView: View {
    let scrum: DailyScrum
    var body: some View {
      Self._printChanges()
      return Text("Hello, World!")
          .background(scrum.theme.mainColor)
    }
}

我在控制台中得到的是：

在主捆绑包的资产目录中找不到名为“黄色”的颜色 （/Users/______/Library/Developer/Xcode/UserData/Previews/Simulator 设备/id/数据/容器/捆绑/应用程序/id/Test.app）

Answer 2

代码似乎没有问题，所以请尝试重新启动 Xcode，或使用 ⌘+⌥+p 重新加载预览。

此外，下面的代码应该产生与 ExpectedPreview 相同的结果。复制这个并继续教程怎么样？

import SwiftUI

struct CardView: View {
    let scrum: DailyScrum
    var body: some View {
        Text("Hello, World!")
    }
}


struct CardView_Previews: PreviewProvider {
    static var scrum = DailyScrum.sampleData[0] // <-- get first item
    static var previews: some View {
        CardView(scrum: scrum)
            .background(scrum.theme.mainColor) // <-- get the mainColor of the first item
    }
}

import Foundation

struct DailyScrum {
    var title: String
    var attendees: [String]
    var lengthInMinutes: Int
    var theme: Theme
}

extension DailyScrum {
    static let sampleData: [DailyScrum] =
    [
        DailyScrum(title: "Design",
                   attendees: ["Cathy", "Daisy", "Simon", "Jonathan"],
                   lengthInMinutes: 10,
                   theme: .yellow), // <-- assign yellow to the first item's theme which referred to the `Theme.swift`
        // others
    ]
}

import SwiftUI

enum Theme: String {
    case indigo
    case magenta
    case navy
    case oxblood
    case purple
    case yellow
    
    var accentColor: Color {
        switch self {
        case /* ...others */ .yellow: return .black // <-- Declare the yellow key for accent color
        case .indigo, .magenta, .navy, .oxblood, .purple: return .white
        }
    }
    var mainColor: Color {
        Color(rawValue)
    }
}