如何在 SwiftUI 中实现文本字段列表而不破坏删除

When I

1. 在 XCode 中创建主从应用程序
2. 使用核心数据
3. 向事件模型添加一个新字段（例如title as String)
4. 改变MasterView对此实施

struct MasterView: View {
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Event.timestamp, ascending: true)], 
        animation: .default)
    var events: FetchedResults<Event>

    @Environment(\.managedObjectContext)
    var viewContext

    var body: some View {
        List {
            ForEach(events, id: \.self) { event in
                NavigationLink(
                    destination: DetailView(event: event)
                ) {
                    TextField("Title", text: Binding(ObservedObject<Event>(wrappedValue: event).projectedValue.title)!)
                }
            }.onDelete { indices in
                self.events.delete(at: indices, from: self.viewContext)
            }
        }
    }
}

，即交换出Text for TextField与适当的绑定title的属性event对象，XCode 会愉快地编译，并且只要我不尝试从列表中删除，应用程序就会以预期的行为运行。

当我尝试删除一个Event，它因这个堆栈跟踪而崩溃

* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
    #0: [33m`SwiftUI.BindingOperations.ForceUnwrapping.get(base: Swift.Optional<A>) -> A[0m
    #1: [33m`protocol witness for SwiftUI.Projection.get(base: A.Base) -> A.Projected in conformance SwiftUI.BindingOperations.ForceUnwrapping<A> : SwiftUI.Projection in SwiftUI[0m
    #2: [33m`SwiftUI.(ProjectedLocation in _5A9440699EF65619D724050F1A6941EE).update(context: AttributeGraph.AttributeContext<SwiftUI.VoidAttribute>, state: inout Swift.Optional<Any>) -> (B.Projected, Swift.Bool)[0m
    #3: [33m`SwiftUI.LocationBox.update(context: AttributeGraph.AttributeContext<SwiftUI.VoidAttribute>, state: inout Swift.Optional<Any>) -> (A.Value, Swift.Bool)[0m
    #4: [33m`SwiftUI.Binding.(ScopedLocation in _5436F2B399369BE3B016147A5F8FE9F2).update(context: AttributeGraph.AttributeContext<SwiftUI.VoidAttribute>, state: inout Swift.Optional<Any>) -> (A, Swift.Bool)[0m
    #5: [33m`protocol witness for SwiftUI.Location.update(context: AttributeGraph.AttributeContext<SwiftUI.VoidAttribute>, state: inout Swift.Optional<Any>) -> (A.Value, Swift.Bool) in conformance SwiftUI.Binding<A>.(ScopedLocation in _5436F2B399369BE3B016147A5F8FE9F2) : SwiftUI.Location in SwiftUI[0m
    #6: [33m`SwiftUI.LocationBox.update(context: AttributeGraph.AttributeContext<SwiftUI.VoidAttribute>, state: inout Swift.Optional<Any>) -> (A.Value, Swift.Bool)[0m
    #7: [33m`SwiftUI.Binding.(Box in _5436F2B399369BE3B016147A5F8FE9F2).update(property: inout SwiftUI.Binding<A>, context: AttributeGraph.AttributeContext<SwiftUI.VoidAttribute>) -> Swift.Bool[0m
    #8: [33m`static SwiftUI.(BoxVTable in _68550FF604D39F05971FE35A26EE75B0).update(ptr: Swift.UnsafeMutableRawPointer, property: Swift.UnsafeMutableRawPointer, context: AttributeGraph.AttributeContext<SwiftUI.VoidAttribute>) -> Swift.Bool[0m
    #9: [33m`SwiftUI._DynamicPropertyBuffer.update(container: Swift.UnsafeMutableRawPointer, context: AttributeGraph.AttributeContext<SwiftUI.VoidAttribute>) -> Swift.Bool[0m
    #10: [33m`SwiftUI.(DynamicPropertyBody in _9F92ACD17B554E8AB7D29ABB1E796415).update(context: inout AttributeGraph.AttributeContext<SwiftUI.(DynamicPropertyBody in _9F92ACD17B554E8AB7D29ABB1E796415)<A>>) -> ()[0m
    #11: [33m`protocol witness for static AttributeGraph.UntypedAttribute._update(_: Swift.UnsafeMutableRawPointer, graph: __C.AGGraphRef, attribute: __C.AGAttribute) -> () in conformance SwiftUI.(DynamicPropertyBody in _9F92ACD17B554E8AB7D29ABB1E796415)<A> : AttributeGraph.UntypedAttribute in SwiftUI[0m
    #12: [33m`partial apply forwarder[0m
    #13: [33m`AG::Graph::UpdateStack::update[0m
    #14: [33m`AG::Graph::update_attribute[0m
    #15: [33m`AG::Subgraph::update[0m
    #16: [33m`SwiftUI.ViewGraph.(runTransaction in _D63C4EB7F2B205694B6515509E76E98B)(in: __C.AGGraphRef) -> ()[0m
    #17: [33m`closure #1 (__C.AGGraphRef) -> (prefs: Swift.Bool, idealSize: Swift.Bool, outputs: SwiftUI.ViewGraph.Outputs) in SwiftUI.ViewGraph.updateOutputs(at: SwiftUI.Time) -> ()[0m
    #18: [33m`SwiftUI.ViewGraph.updateOutputs(at: SwiftUI.Time) -> ()[0m
    #19: [33m`closure #1 () -> () in closure #1 () -> () in (extension in SwiftUI):SwiftUI.ViewRendererHost.render(interval: Swift.Double, updateDisplayList: Swift.Bool) -> ()[0m
    #20: [33m`closure #1 () -> () in (extension in SwiftUI):SwiftUI.ViewRendererHost.render(interval: Swift.Double, updateDisplayList: Swift.Bool) -> ()[0m
    #21: [33m`(extension in SwiftUI):SwiftUI.ViewRendererHost.render(interval: Swift.Double, updateDisplayList: Swift.Bool) -> ()[0m
    #22: [33m`closure #1 () -> () in SwiftUI._UIHostingView.requestImmediateUpdate() -> ()[0m
    #23: [33m`reabstraction thunk helper from @escaping @callee_guaranteed () -> () to @escaping @callee_unowned @convention(block) () -> ()[0m
    #24: [33m`_dispatch_call_block_and_release[0m
    #25: [33m`_dispatch_client_callout[0m
    #26: [33m`_dispatch_main_queue_callback_4CF[0m
    #27: [33m`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__[0m
    #28: [33m`__CFRunLoopRun[0m
    #29: [33m`CFRunLoopRunSpecific[0m
    #30: [33m`GSEventRunModal[0m
    #31: [33m`UIApplicationMain[0m
  * #32: [33m`main[0m at AppDelegate.swift:13
    #33: [33m`start[0m

我已经尝试过这个：SwiftUI 持有对已删除核心数据对象的引用导致崩溃但无济于事。我还尝试将文本字段提取到单独的视图类中并使用适当的属性包装器。

我想我在某种程度上滥用了基础设施（绑定、可观察对象等）。我应该如何使用它们来实现列表中的文本字段？

代替

TextField("标题", 文本: Binding(ObservedObject(wrappedValue: 事件）.projectedValue.title）！）

Use

TextField("Title", text: Binding<String>(
                   get: {event.title ?? "<none>"}, set: {event.title = $0}))

已测试并适用于 Xcode 11.2、iOS 13.2