Swift 自定义视图可以工作，但其预览不会编译

对于我在Github准备的问题：

它是一个具有自定义视图的快捷界面列表：

正如您在上面的屏幕截图中看到的，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

行上的连续声明必须用“；”分隔


这里发生了什么，请帮助我（一个敏捷的新手）理解

我试着在那里放一个分号，但它没有真正起作用。
你不能在
结构或
类的顶层放这样的命令式代码，顶层是为函数和属性声明保留的

您可以将
topEntity
改为一个计算属性，这样您的命令式赋值就可以进入
{}
中，而不存在于顶层：

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)
    }
}

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)
    }
}