在视图中更新CoreData中的数据及其值 [英] Update data in CoreData and its value in a view

问题描述

我是不熟悉使用Swift和CoreData进行开发的人.我一直在努力与以下代码一起使用，该代码显示一个视图，其中包含有关与CoreData存储的学生的一些信息.视图中显示的问问题"按钮会更新student.questionAskedClass，但视图不会更新其值.

I am new to developing in Swift and CoreData. I've been struggling with the following code which displays a view with some information on a student which is stored with CoreData. The button "Ask question" which is displayed in the view updates student.questionAskedClass but the view does not updates its value.

该值显然在内部进行了更新，因为如果我重新启动该应用程序，则可以看到该值已被更新.但我希望看到它实时更新.

The value is clearly updated internally because if I relaunch the application, I can see that the value has been updated. But I would like to see it updated live.

感谢您的帮助，弗朗索瓦(Francois)

Thanks for your help, Francois

import SwiftUI

struct StudentView: View {
  @Environment(\.managedObjectContext) var managedObjectContext

  var student: Student

  var body: some View {
    VStack(alignment: .leading) {
      Text("\(student.firstName)").font(.headline).foregroundColor(Color.black)
      Text("\(student.lastName)").font(.headline).foregroundColor(Color.gray)
      Spacer().frame(height: 10)
      Text("\(student.email)").font(.headline).foregroundColor(Color.gray)
      Spacer().frame(height: 10)
      Text("Number of questions asked: \(student.questionAskedClass)").font(.headline).foregroundColor(Color.gray)
      Button(action: {
        self.askQuestion()
      }) {
        Text("Ask question")
      }
    }
  }

  func askQuestion() {
    self.managedObjectContext.performAndWait {
      self.student.questionAskedClass += 1
      try? self.managedObjectContext.save()
    }
  }
}

推荐答案

您需要的只是

struct StudentView: View {
  @Environment(\.managedObjectContext) var managedObjectContext

  @ObservedObject var student: Student     // << here !!

通过Xcode 11.4/iOS 13.4测试

Tested with Xcode 11.4 / iOS 13.4

这篇关于在视图中更新CoreData中的数据及其值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！