Question

当editMode为.inactive时，如何使列表显示一组选定项；而当editMode为.active时，如何使所有可选选项均如此，以便用户可以更改一组选定项？这是我尝试过的：

import SwiftUI

struct SelectionView: View {
    @Environment(\.editMode) var editMode
    @State var selectedItems = Set<String>(["1-item", "2-item", "3-item", "4-item"])
    let allItems = ["1-item", "2-item", "3-item", "4-item"]
    var items: [String] {
        if editMode?.wrappedValue == .inactive {
            return Array(selectedItems)
        }
        else {
            return allItems
        }
    }

    var body: some View {
        NavigationView {
            List(items, id: \.self, selection: $selectedItems) { item in
                Text(item)
            }
            .navigationBarItems(trailing: EditButton())
            .navigationBarTitle("Items")
        }
    }
}

所选数组现在是无序的，因为它是从集合生成的，我最终希望以正确的顺序进行排列。但是我首先尝试使列表按原样工作。

Answer 1

这里是对我有用的方法。不幸的是，由于List内部细节（或错误）的原因，它并不完全好。

这个想法是切换List的容器以根据所选项目过滤其中的一个，而切换本身取决于手动跟踪EditMode

无论如何，它都能正常工作（在Xcode 11.2 / iOS 13.2上以及在预览版中都经过测试）

struct SelectionView: View {
    @State var editMode: EditMode = .inactive // ! Needed manual to track states

    @State var selectedItems = Set<String>(["1-item", "2-item", "3-item", "4-item"])
    let allItems = ["1-item", "2-item", "3-item", "4-item"]
    var items: [String] {
        allItems.filter { self.selectedItems.contains($0) }
    }

    @State var applyFilter = false
    var body: some View {
        NavigationView {
            VStack {
                List(applyFilter ? items : allItems, id: \.self,
                     selection: $selectedItems) { item in
                        Text(item)
                }
                .navigationBarItems(trailing: EditButton())
                .navigationBarTitle("Items")
            }
//            .environment(\.editMode, $editMode) // << this is how it should be, but crash
            .environment(\.editMode, Binding<EditMode>(get: { self.editMode },
               set: {
                    self.editMode = $0

                    // !!! below is needed workaround, because applying filter directly
                    // on close EditMode result in crash due to cached List internals
                    // until switch EditMode animation is finished completely
                    if $0 == .inactive {
                        DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) {
                            self.applyFilter = true
                        }
                    } else {
                        self.applyFilter = false
                    }
            }))
        }
    }
}

如何仅显示SwiftUI列表中的选定项目？

1 个答案: