swift - Xcode Beta 6 "Type of expression is ambiguous without more context"导航链接

Question

自从今天早些时候更新到 Xcode Beta 6 后，我的应用程序将不再构建，它在 Beta 5 和更早版本中运行良好。

这是带有错误消息的文件中的代码，尽管我目前知道这并不一定意味着错误实际出处。

import SwiftUI

struct JobView_Table : View {

    @ObservedObject var jobList: JobDetailViewModel = JobDetailViewModel()

    var body: some View {

        NavigationView {

            List {
                ForEach($jobList.jobDetails) { job in
                    NavigationLink(destination: JobDetailHost(jobDetails: job)) { // ERROR: "Type of expression is ambiguous without more context"
                        JobView_List(jobDetails: job)
                    }
                }
            }

            .navigationBarTitle(Text("My Jobs"))
            .onAppear(perform: fetchData)
            .onAppear(perform: {
                print("Hello!")
            })

        }
    }

    private func fetchData() {
        return(jobList.updateDetails())
    }
}

包含数据的结构正确地符合以下协议(protocol)。

struct JobDetails: Codable, Identifiable, Equatable, Hashable { 
    ...

    ...
}

这是向 JobView_Table 提供数据的类。

import Foundation
import UIKit
import Combine

class JobDetailViewModel: ObservableObject, Identifiable {

    @Published var jobDetails: [JobDetails] = []

    func updateDetails() {
        self.jobDetails = DataManager().fetchJobList()
    }

}

最后是通过 NavigationLink 链接到的目标 View 。

struct JobDetailHost: View {

    @Environment(\.editMode) var mode
    @Binding var jobDetails: JobDetails


    var body: some View {

        VStack {
            JobDetailView(jobDetails: jobDetails)
        }
        .navigationBarItems(trailing: EditButton())
    }

}

我注意到其他一些人似乎也有类似的问题，即在下面列出的两个问题中，但目前探索这些问题的答案对我没有帮助。 SwiftUI Xcode 11 beta 5 / 6: Type of expression is ambiguous without more context

SwiftUI: Why does ForEach($strings) (text: Binding) not build?

编辑:

我已经尝试实现 Fabian 的建议，这已经消除了错误，但是列表中没有填充任何内容。

这是调整后的 List 代码，它编译成功，但在运行应用程序时列表未填充。

List {
    ForEach(jobList.jobDetails.indexed(), id: \.1.id) { (index, job) in
            NavigationLink(destination: JobDetailHost(jobDetails: self.$jobList.jobDetails[index])) {
                        Text(job.jobName)
                    }
     }
}

下面没有使用ForEach，丢弃了NavigationLink，还是不行。

List(jobList.jobDetails.indexed(), id: \.1.id) { (index, job) in
                Text(job.jobName)
            }

Answer 1

我会引用 macOS Catalina 10.15 Beta 6 Release Notes :

The Binding structure’s conditional conformance to the Collection protocol is removed. (51624798)

If you have code such as the following:

struct LandmarkList: View {
    @Binding var landmark: [Landmark]

    var body: some View {
        List(landmarks) { landmark in
            Toggle(landmark.value.name, isOn: landmark[\.isFavorite])
        }
    }
}

Define the following collection type:

struct IndexedCollection<Base: RandomAccessCollection>: RandomAccessCollection {
    typealias Index = Base.Index
    typealias Element = (index: Index, element: Base.Element)

    let base: Base

    var startIndex: Index { base.startIndex }

    var endIndex: Index { base.endIndex }

    func index(after i: Index) -> Index {
        base.index(after: i)
    }

    func index(before i: Index) -> Index {
        base.index(before: i)
    }

    func index(_ i: Index, offsetBy distance: Int) -> Index {
        base.index(i, offsetBy: distance)
    }

    subscript(position: Index) -> Element {
        (index: position, element: base[position])
    }
}

extension RandomAccessCollection {
    func indexed() -> IndexedCollection<Self> {
        IndexedCollection(base: self)
    }
}

Then, update your code to:

struct LandmarkList: View {
    @Binding var landmarks: [Landmark]

    var body: some View { // Does often give error on id: \.1.id
        List(landmarks.indexed(), id: \.1.id) { (index, landmark) in
            Toggle(landmark.name, isOn: self.$landmarks[index].isFavorite)
        }
    }
}

您的代码还需要一个 Binding<[JobDetails]>与 $jobList.jobDetails ，但是Binding<[JobDetails]>不再符合 Collection 协议(protocol)。

但是请注意上面的解决方案，我遇到了 \.1.id 的情况未被识别，因为编译器不理解 \.1指的是元组中的第二个元素 IndexedCollection定义，但有可能我用错了。可以重写它，但它可以正常工作。

使用 IndexedCollection 的例子

struct AnotherIndexedView_NeedsEnv: View {
    @EnvironmentObject var modalManager: ModalManager

    var body: some View {
        ZStack {
            SwiftUI.ForEach(modalManager.modals.indexed()) { m in
                ModalView(currentModal: self.$modalManager.modals[m.index]).environmentObject(self.modalManager)
            }
        }.onAppear(perform: {self.modalManager.fetchContent()})
    }
}