ios - SwiftUI 预览不显示(无错误)

Question

我有以下 TransactionsListView.swift 的 PreviewProvider 代码:

struct TransactionsListView_Previews: PreviewProvider {

    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        let transaction = NPTransaction(context: context)
        transaction.date = Date()
        transaction.income = true
        transaction.type = "morning"
        transaction.value = 1200
        transaction.notes = "notes"
        return TransactionsListView(filter: true, startDate: Date()).environment(\.managedObjectContext, context)
    }

}

预览未显示。有提示Build Succeeded，没有错误信息，但是Canvas是空的。我做错了什么？

P.s.我正在使用 CoreData，并且有 1 个名为 NPTransaction 的实体，它有 5 个属性:日期、收入、注释、类型、值。

Answer 1

由于 Xcode 没有给我任何错误，所以不容易猜测。我需要在预览中将addingTimeInterval 添加到Date() 中。工作代码:

结构 TransactionsListView_Previews:PreviewProvider {

static var previews: some View {
    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    let transaction = NPTransaction(context: context)
    transaction.date = Date()
    transaction.income = true
    transaction.type = "morning"
    transaction.value = 1200
    transaction.notes = "notes"
    return TransactionsListView(filter: true, startDate: Date().addingTimeInterval(-86400 * 30)).environment(\.managedObjectContext, context)
}

}

感谢@CranialDev，他在这里帮助了我:https://stackoverflow.com/a/59970329/12315994