SwiftUI CoreData 崩溃预览

Question

我有以下代码来绘制汽车列表，数据存储在 coredata 中。

但是，当我添加从数据库获取数据的代码行时，swiftui 预览似乎会中断。

错误日志显示以下内容:

PotentialCrashError: test app.app may have crashed

mileage app.app may have crashed. Check ~/Library/Logs/DiagnosticReports for any crash logs from your application.

==================================

| Error Domain=com.apple.dt.ultraviolet.service Code=12 "Rendering service was interrupted" UserInfo={NSLocalizedDescription=Rendering service was interrupted}

这是 foreach 开始和结束部分导致错误的代码:

import SwiftUI

struct CarListView: View {

    @Environment(\.managedObjectContext) var managedObjectContext
    @FetchRequest(fetchRequest: Car.all()) var cars: FetchedResults<Car>

    var body: some View {

        NavigationView {
            ZStack {
                List {
                    Section(header: Text("Cars")) {
                        ForEach(self.cars, id: \.numberPlate) { car in
                            HStack {
                                VStack(alignment: .leading) {
                                    Text(car.name)
                                    Text(car.numberPlate)
                                }
                            }
                        }
                    }
                }
            }
        }
    }

}

struct CarListView_Previews: PreviewProvider {
    static var previews: some View {
        CarListView()
    }
}

Answer 1

该问题似乎与它无法以某种方式获取允许在预览模式下获取数据的上下文有关。通过在预览模式下手动执行此操作，可以解决该问题。

struct CarListView_Previews: PreviewProvider {
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        return CarListView().environment(\.managedObjectContext, context)

    }
}