将对象与返回False的自身进行比较

Question

我有一个实现平等协议的类，它使用一个UUID字段进行比较：

class MemberViewModel {
    private static var entities: [MemberViewModel] = []
    private var entity: Member

    let id = UUID()

    init(_ entity: Member) {
        self.entity = entity
    }

    static func members() -> [MemberViewModel] {
        entities.removeAll()

        try? fetch().forEach { member in
            entities.append(MemberViewModel(member))
        }

        return entities
    }
}

extension MemberViewModel: Equatable {
    static func == (lhs: MemberViewModel, rhs: MemberViewModel) -> Bool {
        return lhs.id == rhs.id
    }
}

然后，我有一个视图，创建图标，当点击这些图标时，应该显示一个笔画来表示它是“被选中的”：

struct MyView: View {
    @State var selectedMember: MemberViewModel? = nil

    var body: some View {
        let members = MemberViewModel.members()

        ScrollView(.horizontal, showsIndicators: true) {
            HStack(alignment: .top, spacing: 4) {
                ForEach (members, id: \.id) { member in
                    var isSelected: Bool = selectedMember == member

                    Circle()
                        .fill(Color(.red))
                        .frame(width: 48, height: 48)
                        .overlay() {
                            if isSelected {
                                Circle()
                                    .stroke(Color(.black), lineWidth: 2)
                            }
                        }
                        .onTapGesture { selectedMember = member }
                }
            }
        }
    }
}

我尝试过多种方法设置isSelected，包括another SO question中的以下内容

let isSelected = Binding<Bool>(get: { self.selectedMember == member }, set: { _ in })

使用断点进行调试时，isSelected的值总是为false。

我使用的是XCode版本14.0.1 (14A400)和SWIFT5.7。

Answer 1

将let members = MemberViewModel.members()放在var body: some View {...}前面，而不是放在里面，如下所示：

let members = MemberViewModel.members()  // <-- here 

var body: some View {
  ...
} 

由于您奇怪的代码结构，每次刷新let members = MemberViewModel.members()时，body都会被重做。既然UUID是重新生成的..。您可以猜到，ids现在到处都是，不等于selectedMember。

换句话说，对象比较是有效的，但您并不是在比较您的想法。

Answer 2

使用下面的示例，希望您能得到这个想法。

模型

struct Member {
    
    let id = UUID()
    
}

extension Member: Equatable {
    static func == (lhs: Member, rhs: Member) -> Bool {
        return lhs.id == rhs.id
    }
}

class MemberViewModel: ObservableObject {
    // each time you update the entities, view vill be updated
    @Published var entities: [Member] = []
    
    func fetchMembers() {
        entities.removeAll()

        // your code to fetch members
        try? fetch().forEach { member in
           entities.append(member)
        }
        
    }
}

MyView

struct MyView: View {
    
    @StateObject private var modelData = MemberViewModel()
    @State private var selectedMember: Member? = nil

    var body: some View {
        
        ScrollView(.horizontal, showsIndicators: true) {
            HStack(alignment: .top, spacing: 4) {
                ForEach (modelData.entities, id: \.id) { member in

                    Circle()
                        .fill(Color(.red))
                        .frame(width: 48, height: 48)
                        .overlay() {
                            if selectedMember == member {
                                Circle()
                                    .stroke(Color(.black), lineWidth: 2)
                            }
                        }
                        .onTapGesture { selectedMember = member }
                }
            }
        }.onAppear {
            modelData.fetchMembers()
        }
    }
}