SwiftUI

Question

如何创建一个表单，其中的元素会根据其首字母自动分为多个部分，并在右侧添加字母表跳线以显示以所选字母开头的元素（就像“联系人”应用程序一样）？

我还注意到一个奇怪的事情，我不知道如何重新创建：并非所有字母都显示，其中一些显示为“•”。然而，当你点击它们时，它们无论如何都会带你到相应的字母。我尝试在 ZStack 中使用 ScrollView(.vertical) 并将 .scrollTo(selection) 添加到按钮的操作中，但是 1) 它没有滚动到我想要的选择 2) 当我点击“•”时，就好像我正在点击所有这些因为他们都做了点击动画 3) 我无法按照我的意愿划分列表。我有这个：

import SwiftUI

struct ContentView: View {

let alphabet = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W", "X","Y", "Z"]
let values = ["Avalue", "Bvalue", "Cvalue", "Dvalue"]

var body: some View {
           ScrollViewReader{ scrollviewr in
               ZStack {
                   ScrollView(.vertical) {
                       VStack {
                           ForEach(alphabet, id: \.self) { letters in
                               Button(letters){
                                   withAnimation {
                                    scrollviewr.scrollTo(letters)
                                   }
                               }
                           }
                       }
                   }.offset(x: 180, y: 120)

                VStack {
                    
                ForEach(values, id: \.self){ vals in
                               Text(vals).id(vals)
                   }
                }
               }
           }
   }
}

但我想要这样：

Answer 1

import SwiftUI

struct AlphabetSort2: View {
    let alphabet = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W", "X","Y", "Z"]
    let values = ["Avalue", "Bvalue", "Cvalue", "Dvalue", "Mvalue", "Zvalue"]
    var body: some View {
        ScrollView {
            ScrollViewReader { value in
                ZStack{
                    List{
                        ForEach(alphabet, id: \.self) { letter in
                            Section(header: Text(letter)) {
                                ForEach(values.filter { [=10=].hasPrefix(letter) }, id: \.self) { vals in
                                    Text(vals).id(vals)
                                }
                            }.id(letter)
                        }
                    }
                    HStack{
                        Spacer()
                        VStack {
                            ForEach(0..<alphabet.count, id: \.self) { idx in
                                Button(action: {
                                    withAnimation {
                                        value.scrollTo(alphabet[idx])
                                    }
                                }, label: {
                                    Text(idx % 2 == 0 ? alphabet[idx] : "\u{2022}")
                                })
                            }
                        }
                    }
                }
            }
        }
    }
}

struct AlphabetSort2_Previews: PreviewProvider {
    static var previews: some View {
        AlphabetSort2()
    }
}

Answer 2

为字母跳线添加一个上下滑动的动作，这样我们就可以得到一个类似 UILocalizedIndexCollation 的滑动效果，它适用于查看和添加模式，但是删除，我猜是由于 SwiftUI 的 UI 刷新机制。

extension String {
    static var alphabeta: [String] {
        var chars = [String]()
        for char in "abcdefghijklmnopqrstuvwxyz#".uppercased() {
            chars.append(String(char))
        }
        return chars
    }
}

struct Document: View {
    @State var items = ["Alpha", "Ash", "Aman", "Alisia", "Beta", "Baum", "Bob", "Bike", "Beeber", "Beff", "Calipha", "Cask", "Calf", "Deamon", "Deaf", "Dog", "Silk", "Seal", "Tiger", "Tom", "Tan", "Tint", "Urshinabi", "Verizon", "Viber", "Vein", "Wallet", "Warren", "Webber", "Waiter", "Xeon", "Young", "Yoda", "Yoga", "Yoger", "Yellow", "Zeta"]
    var body: some View {
        ScrollViewReader { scrollView in
            HStack {
                List {
                    ForEach(String.alphabeta, id: \.self){ alpha in
                        let subItems = items.filter({[=10=].starts(with: alpha)})
                        if !subItems.isEmpty {
                            Section(header: Text(alpha)) {
                                ForEach(subItems, id: \.self) { item in
                                    Text(item)
                                }.onDelete(perform: { offsets in
                                    items.remove(at: offsets.first!)
                                })
                            }.id(alpha)
                        }

                    }
                }
                
                VStack{
                    VStack {
                        SectionIndexTitles(proxy: scrollView, titles: retrieveSectionTitles()).font(.footnote)
                    }
                    .padding(.trailing, 10)
                }
            }
        }
//        .navigationBarTitleDisplayMode(.inline)
//        .navigationBarHidden(true)
    }
    
    func retrieveSectionTitles() ->[String] {
        var titles = [String]()
        titles.append("@")
        for item in self.items {
            if !item.starts(with: titles.last!){
                titles.append(String(item.first!))
            }
        }
        titles.remove(at: 0)
        if titles.count>1 && titles.first! == "#" {
            titles.append("#")
            titles.removeFirst(1)
        }
        return titles
    }
}

struct Document_Previews: PreviewProvider {
    static var previews: some View {
        Document()
    }
}

struct SectionIndexTitles: View {
    class IndexTitleState: ObservableObject {
        var currentTitleIndex = 0
        var titleSize: CGSize = .zero
    }
    
    let proxy: ScrollViewProxy
    let titles: [String]
    @GestureState private var dragLocation: CGPoint = .zero
    @StateObject var indexState = IndexTitleState()
    
    var body: some View {
        VStack {
            ForEach(titles, id: \.self) { title in
                Text(title)
                    .foregroundColor(.blue)
                    .modifier(SizeModifier())
                    .onPreferenceChange(SizePreferenceKey.self) {
                        self.indexState.titleSize = [=10=]
                    }
                    .onTapGesture {
                        proxy.scrollTo(title, anchor: .top)
                    }
            }
        }
        .gesture(
            DragGesture(minimumDistance: indexState.titleSize.height, coordinateSpace: .named(titles.first))
                .updating($dragLocation) { value, state, _ in
                    state = value.location
                    scrollTo(location: state)
                }
        )
    }
    
    private func scrollTo(location: CGPoint){
        if self.indexState.titleSize.height > 0{
            let index = Int(location.y / self.indexState.titleSize.height)
            if index >= 0 && index < titles.count {
                if indexState.currentTitleIndex != index {
                    indexState.currentTitleIndex = index
                    print(titles[index])
                    DispatchQueue.main.async {
                        let impactMed = UIImpactFeedbackGenerator(style: .medium)
                            impactMed.impactOccurred()
//                        withAnimation {
                            proxy.scrollTo(titles[indexState.currentTitleIndex], anchor: .top)
//                        }
                    }
                }
            }
        }
    }
    
}

struct SizePreferenceKey: PreferenceKey {
    static var defaultValue: CGSize = .zero

    static func reduce(value: inout CGSize, nextValue: () -> CGSize) {
        value = nextValue()
    }
}

struct SizeModifier: ViewModifier {
    private var sizeView: some View {
        GeometryReader { geometry in
            Color.clear.preference(key: SizePreferenceKey.self, value: geometry.size)
        }
    }

    func body(content: Content) -> some View {
        content.background(sizeView)
    }
}

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