swift - 自定义视图有效，但其预览无法编译

Question

对于这个问题，我在 Github准备了一个简单的测试项目：

它是一个带有自定义 View TopRow.swift的 SwiftUI 列表：

struct TopRow: View {
    let top:TopEntity
    
    var body: some View {
        HStack {
            Circle()
                .frame(width: 60, height: 60)
            Spacer()
            Text(top.given ?? "Unknown Person")
                .frame(minWidth: 60, maxWidth: .infinity, alignment: .leading)
            Spacer()
            VStack {
                Text("Elo rating: \(top.elo)")
                Text("Average time: \(top.avg_time ?? "")")
                Text("Average score: \(String(top.avg_score))")
            }.fixedSize(horizontal: true, vertical: false)
        }.font(.footnote)
    }
}

正如您在上面的屏幕截图中看到的那样，它工作正常。

但是它的预览不起作用：

struct TopRow_Previews: PreviewProvider {
    static var topEntity = TopEntity(context: PersistenceController.preview.container.viewContext)
    topEntity.uid = 19265
    topEntity.elo = 2659
    topEntity.given = "Alex"
    topEntity.motto = "TODO"
    topEntity.photo = "https://slova.de/words/images/female_happy.png"
    topEntity.avg_score = 18.8
    topEntity.avg_time = "03:06"

    static var previews: some View {
        TopRow(top: topEntity)
            .padding()
            .previewLayout(.sizeThatFits)
    }
}

Xcode 报告语法错误Consecutive declarations on a line must be separated by ';'

那里发生了什么，请帮助我（一个 Swift 新手）理解。

我试图在那里放一个分号，但它并没有真正起作用。

Answer 1

您不能将这样的命令式代码放在 a 的顶层struct或class- 顶层保留用于函数和属性的声明。

您可以topEntity改为使用计算属性 - 这样您的命令式分配可以进入内部{ }并且不存在于顶层：

struct TopRow_Previews: PreviewProvider {
    static var topEntity : TopEntity {
        var topEntity = TopEntity(context: PersistenceController.preview.container.viewContext)
        topEntity.uid = 19265
        topEntity.elo = 2659
        topEntity.given = "Alex"
        topEntity.motto = "TODO"
        topEntity.photo = "https://slova.de/words/images/female_happy.png"
        topEntity.avg_score = 18.8
        topEntity.avg_time = "03:06"
        return topEntity
    }

    static var previews: some View {
        TopRow(top: topEntity)
            .padding()
            .previewLayout(.sizeThatFits)
    }
}