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我使用 ObservableObject 作为数据源在 SwiftUI 中实现了一个分组表。嵌套的 ForEach 用于生成每个部分。EditMode() 按钮切换该 Environment 属性。在编辑模式下，当删除操作完成时，被删除的行（意外地）保留在屏幕上。（即使该对象已从数据源数组中删除。）当用户返回正常查看模式时，该对象迟迟会从表中删除。

在此处输入图像描述

为了尝试追踪错误：

  • 数据源对象符合 Hashable、Identifiable 和 Equatable。

  • 实现了一个简单的删除操作（即删除@Published 属性中的第一个对象）

  • 数据源/视图模型存储在@EnvironmentData 对象中

所以简单的问题是我做错了什么会导致 SwiftUI 不会立即在一个非常简单的（我认为）分组（按部分）列表上反映 EditMode 中的删除操作？

struct ContentView: View {

    @EnvironmentObject var vm: AppData

    var body: some View {

        NavigationView {

            List {
                ForEach(vm.folderSource) { (folder: Folder)   in
                    return Section(header: Text(folder.title)) {
                        //this is where problem originates. When I drop in a new full-fledged View struct, UI updates stop working properly when .onDelete is called from this nested View
                        FolderView(folder: folder)
                    }
                }
            }.listStyle(GroupedListStyle())
                .navigationBarItems(trailing: EditButton())
        }
    }
}

struct FolderView: View {

    var folder: Folder

    @EnvironmentObject var vm: AppData


    var body: some View {
        //I'm using a dedicated View inside an outer ForEach loop to be able to access a data-source for each dynamic view.

        let associatedProjects = vm.projects.filter{$0.folder == folder}

        return ForEach(associatedProjects) { (project: Project) in
            Text(project.title.uppercased())
            // dumbed-down delete, to eliminate other possible issues preventing accurate Dynamic View updates
        }.onDelete{index in self.vm.delete()}
    }
}


//view model
class AppData: ObservableObject {



    let folderSource: [Folder]
    @Published var projects: [Project]

    func delete() {
        //dumbed-down static delete call to try to find ui bug
        self.projects.remove(at: 0)
        //
    }


    init() {
        let folders = [Folder(title: "folder1", displayOrder: 0), Folder(title: "folder2", displayOrder: 1), Folder(title: "folder3", displayOrder: 2)  ]

        self.folderSource = folders


        self.projects = {

            var tempArray = [Project]()
            tempArray.append(Project(title: "project 0", displayOrder: 0, folder: folders[0]  ))
            tempArray.append(Project(title: "project 1", displayOrder: 1, folder: folders[0]  ))
            tempArray.append(Project(title: "project 2", displayOrder: 2, folder: folders[0]  ))


            tempArray.append(Project(title: "project 3", displayOrder: 0, folder: folders[1]  ))
            tempArray.append(Project(title: "project 4", displayOrder: 1, folder: folders[1]  ))
            tempArray.append(Project(title: "project 5", displayOrder: 2, folder: folders[1]  ))


            tempArray.append(Project(title: "project 6", displayOrder: 0, folder: folders[2]  ))
            tempArray.append(Project(title: "project 7", displayOrder: 1, folder: folders[2]  ))
            tempArray.append(Project(title: "project 8", displayOrder: 2, folder: folders[2]  ))

            return tempArray
        }()

    }

}


//child entity many-to-one (Folder)
class Project: Hashable, Equatable, Identifiable {

    let id = UUID()
    let title: String
    let displayOrder: Int
    let folder: Folder

    init(title: String, displayOrder: Int, folder: Folder) {
        self.title = title
        self.displayOrder = displayOrder
        self.folder = folder
    }

    static func == (lhs: Project, rhs: Project) -> Bool {
        lhs.id == rhs.id

    }

    func hash(into hasher: inout Hasher) {
        hasher.combine(id)
    }
}

//parent entity: Many Projects have one Folder
class Folder: Hashable, Equatable, Identifiable {

    let id = UUID()
    let title: String
    let displayOrder: Int


    init(title: String, displayOrder: Int) {
        self.title = title
        self.displayOrder = displayOrder
    }

    //make Equatable
    static func == (lhs: Folder, rhs: Folder) -> Bool {
        lhs.id == rhs.id
    }

    //make Hashable
    func hash(into hasher: inout Hasher) {
        hasher.combine(id)
    }
}

在 SceneDelegate.swift

 // Create the SwiftUI view that provides the window contents.
        let contentView = ContentView().environmentObject(AppData())
4

2 回答 2

3

我删除了我之前的答案，因为正如你所指出的，虽然它有效，但这纯粹是巧合。

在这里，您还有另一项工作。它基本上通过不封装第二个ForEach来工作。到目前为止，我发现封装是规避某些错误的好工具。在这种情况下，情况正好相反！

struct ContentView: View {

    @EnvironmentObject var vm: AppData

    var body: some View {

        NavigationView {

            List {
                ForEach(vm.folderSource) { (folder: Folder)   in
                    Section(header: Text(folder.title)) {
//                        FolderView(folder: folder)
                        ForEach(self.vm.projects.filter{$0.folder == folder}) { (project: Project) in
                            Text(project.title.uppercased())
                        }.onDelete{index in
                            self.vm.delete()
                        }
                    }
                }
            }
            .listStyle(GroupedListStyle())
            .navigationBarItems(trailing: EditButton())
        }
    }
}
于 2019-08-24T06:10:21.503 回答
0

因此，奇怪的是，@kontiki 的（有用的）解决方案纯属巧合。事实证明，只需将（未使用的）函数类型变量添加到 FolderView 作为 View 属性参数，并使用该函数参数在 init 方法中设置状态/环境类型的包装变量即可解决问题。这是莫名其妙的。

WORKS（添加设置包装状态属性的函数参数['vm'是AppData视图模型的变量名，符合ObservableObject]。见上文。）

FolderView(folder: folder, onDelete: {self.vm.hello = "ui update bug goes away, even though this function not called"}) //function sets EnvironmentObject-type property

DOESN'T WORK（添加不设置包装状态属性的函数参数

FolderView(folder: folder, onDelete: {print("ui update bug still here")})

DOESN'T WORK（添加非函数参数）

FolderView(folder: folder, unusedString: "ui update bug still here")

我提交了一份错误报告，因为（在我看来）这是出乎意料的行为。

于 2019-08-24T15:50:52.957 回答