swift - 在 SwiftUI 中设置添加项目的限制？

Question

您好，我刚刚开始学习 Swift，我一直想知道如何对可以添加到列表中的项目数量添加限制，例如最多 3 个。

我希望有人能帮助我。

我遵循了本教程系列https://youtu.be/SMt4_WUdKag?list=PLwvDm4VfkdpheGqemblOIA7v3oq0MS30i

这是 ItemStore 文件:

class ItemStore: ObservableObject {
    
    static var shared = ItemStore()
    static var preview = ItemStore()

    @Published var items: [ItemModel] = []{
        
        didSet {
            
            saveItems()
            
        }
        
    }
 
    let itemsKey: String = "items_list"
    
    init() {
        
        getItems()
        
    }
    
    func getItems() {
        guard
            let data = UserDefaults.standard.data(forKey: itemsKey),
            let savedItems = try? JSONDecoder().decode([ItemModel].self, from: data)
        else {return}
        
        self.items  = savedItems
        
    }
    
    func deleteItem (indexSet: IndexSet){
        items.remove(atOffsets: indexSet)
    }
    
    func moveItem (from: IndexSet, to: Int) {
        items.move(fromOffsets: from, toOffset: to)
        
    }
    
    func addItem (title: String) {
        
        let newItem = ItemModel(title: title, isCompleted: false)
        items.append(newItem)
        
    }
    
    func updateItem( item: ItemModel) {
        
        if let index = items.firstIndex(where: { $0.id == item.id}) {
            items [index] = item.updateCompletion()
 
        }
 
    }

    func saveItems() {
        if let encodedData = try? JSONEncoder().encode(items) {
            UserDefaults.standard.set(encodedData, forKey: itemsKey)
 
        }     
    }      
}

这是AddView代码:

struct AddView: View {
    @Environment(\.presentationMode) var presentationMode
    @EnvironmentObject var store: ItemStore
    @State var textFieldText: String = ""
    
    
    @State var alerTitle: String = ""
    @State var showAlert: Bool = false
    
    
    var body: some View {
        ScrollView {
            VStack {
                TextField("Type Here", text: $textFieldText)
                    
                    .padding(.horizontal)
                    .frame(height: 55)
                    .background(Color(UIColor.secondarySystemBackground))
                    .cornerRadius(10)
                    .font(.body.weight(.medium))
                
                Button(action: saveButtonPressed, label: {
                    Text("Save".uppercased())
                        .foregroundColor(.white)
                        .font(.headline)
                        .fontWeight(.bold)
                        .frame(height: 66.0)
                        .frame(maxWidth: .infinity)
                        .background(Color("AccentColor"))
                        .cornerRadius(10)
                    
                })
        }
        .padding(14)
    }
        .navigationTitle("Add an Item ✍️ ")
        .alert(isPresented: $showAlert, content: getAlert)
        
    }
        
        func saveButtonPressed() {
            if textIsAppropriate() {
            
            
            listViewModel.addItem(title: textFieldText)
            presentationMode.wrappedValue.dismiss()
            
            }
        }
    
    func textIsAppropriate() -> Bool {
        if textFieldText.count < 1 {
            alerTitle = "You can't leave the task empty! 🌚"
            showAlert.toggle()
            return false
        }
        return true
    }
    func getAlert() -> Alert {
        return Alert(title: Text(alerTitle))
    }
}




struct AddView_Previews: PreviewProvider {
    static var previews: some View {
        NavigationView {
            AddView()
        }
        .environmentObject(ItemStore.preview)   
    }
}

Answer 1

我查看了您正在遵循的教程。设置限制的最简单方法是将 .disabled(items.count > 3) 添加到用于导航到添加屏幕的 NavigationLink 的末尾。像这样的事情:

NavigationLink(destination: AddView()) {
  Text("Add")
}
.disabled(items.count > 3)