我为TransactionsListView.swift的PreviewProvider提供以下代码:
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。出现一条消息,表示“构建成功”,没有错误消息,但是Canvas为空。我究竟做错了什么?
附言:我正在使用CoreData,并且有1个名为NPTransaction的实体,该实体具有5个属性:日期,收入,注释,类型,值。
由于Xcode没有给我任何错误,所以不容易猜到。我需要在Previews中将addingTimeInterval添加到Date()。工作代码:
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().addingTimeInterval(-86400 * 30)).environment(\.managedObjectContext, context)
}
}
@CranialDev在这里帮助过我的人表示敬意:https : //stackoverflow.com/a/59970329/12315994
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