SwiftUI返回主界面后“购物清单”列表未清空问题求助

开发的购物清单应用功能基本正常，但保存填写完成的新购物清单并返回主界面后，新建清单页面的所有字段均已清空，唯独“Shopping List”列表的内容仍保留。尝试过将item和itemPrice文本框设置为空字符串，但问题仍未解决。

应用代码 #

import Foundation

struct ItemToAdd: Identifiable {
    var id = UUID()
    var itemName: String
    var itemPrice: String
}

import Foundation

struct NewList: Identifiable {
    var id = UUID()
    var storeName: String
    var budget: Float
    var item: String
    var itemPrice: String
}

import Foundation

class HomePageItem: Observable, ObservableObject {
    @Published var items: [NewList] = []
    @Published var itemsToAdd: [ItemToAdd] = []
    
    var totalMoneySpent: Float {
        itemsToAdd.reduce(0) { $0 + $1.itemPrice.floatValue }
    }
}

extension String {
    var floatValue: Float {
        return (self as NSString).floatValue
    }
}

import SwiftUI

struct CreateNewListing: View {
    @EnvironmentObject var settings: HomePageItem
    @State var storeName: String
    @State var budget: Float
    @State var adjustedBudget: Float
    @State var itemName: String
    @State var itemPrice: String
    @State var newBudget: Float
    @State var boolValue = false
    
    var body: some View {
        NavigationStack {
            Form {
                Section(header: Text("Store Name")) {
                    TextField("e.g, Trader Joe's", text: $storeName)
                }
                Section(header: Text("Budget")) {
                    TextField("Enter your budget", value: $budget, format: .number)
                }
                
                Section(header: Text("Enter Item and Price")) {
                    List {
                        HStack {
                            TextField("Item", text: $itemName)
                            TextField("Price", text: $itemPrice)
                        }
                        Button {
                            self.addToList()
                            print(settings.totalMoneySpent)
                        }label: {
                            Text("Add Item")
                        }
                    }
                }
                
                Section(header: Text("Shopping List")) {
                    List {
                        ForEach(settings.itemsToAdd) { item in
                            HStack {
                                Text(item.itemName)
                                Text(item.itemPrice)
                            }
                        }
                        Text("Available Money Left: \(budget - self.settings.totalMoneySpent, specifier: "%.2f")")
                            .foregroundColor(budget - self.settings.totalMoneySpent >= 0 ? Color.green: Color.red)
                    }
                }
            }
            .navigationTitle("Create New List")
            .toolbar {
                Button {
                    settings.items.append(NewList(storeName: storeName, budget: budget, item: itemName, itemPrice: itemPrice))
                    print(settings.items)
                }label: {
                    Text("Save")
                }
            }
        }
        .environmentObject(settings)
    }

    func addToList() {
        guard !itemName.trimmingCharacters(in: .whitespaces).isEmpty else {
            return
        }
        guard !itemPrice.trimmingCharacters(in: .whitespaces).isEmpty else {
            return
        }
        
        boolValue = false
        let newItem = ItemToAdd(itemName: itemName, itemPrice: itemPrice)
        for item in settings.itemsToAdd{
            if (item.itemName.contains(itemName) && (item.itemPrice.contains(itemPrice))){
                boolValue = true
            }
        }
        if boolValue == false{
            settings.itemsToAdd.append(newItem)
            itemName = ""
            itemPrice = ""
        }
    }
}

extension String {
    var floatValue1: Float {
        return (self as NSString).floatValue
    }
}

#Preview {
    CreateNewListing(storeName: "", budget: 0.00, adjustedBudget: 0.00, itemName: "", itemPrice: "", newBudget: 0.00)
        .environmentObject(HomePageItem())
}

import SwiftUI

struct ContentView: View {
    @StateObject var settings: HomePageItem
    
    var body: some View {
        NavigationStack {
            VStack {
                List {
                    ForEach(settings.items) { item in
                        HStack {
                            Text(item.storeName)
                                .multilineTextAlignment(.leading)
                            Spacer()
                            HStack {
                                if(item.budget - settings.totalMoneySpent >= 0){
                                    Text("You saved \(item.budget - settings.totalMoneySpent, specifier: "%.2f")")
                                }
                            }
                        }
                    }
                }
            }
            .toolbar {
                NavigationLink {
                    CreateNewListing(storeName: "", budget: 0.00,adjustedBudget: 0.00, itemName: "", itemPrice: "", newBudget: 0.00)
                } label: {
                    Image(systemName: "plus")
                        .foregroundColor(.orange)
                        .font(.title3)
                }
            }
            .navigationTitle("My Shopping Lists")
        }
        .environmentObject(settings)
    }
}

#Preview {
    ContentView(settings: HomePageItem())
}

核心原因 #

HomePageItem中的itemsToAdd是全局共享的状态变量，保存清单后没有清空，且每次进入新建页面时也未重置，导致旧的购物项一直保留。

修改步骤 #

1. 修正HomePageItem协议冗余
   移除多余的Observable协议，只保留ObservableObject：

   class HomePageItem: ObservableObject {
       @Published var items: [NewList] = []
       @Published var itemsToAdd: [ItemToAdd] = []
       
       var totalMoneySpent: Float {
           itemsToAdd.reduce(0) { $0 + $1.itemPrice.floatValue }
       }
   }
   

2. 保存后清空购物项列表
   在CreateNewListing的保存按钮中添加清空逻辑：

   .toolbar {
       Button {
           settings.items.append(NewList(storeName: storeName, budget: budget, item: itemName, itemPrice: itemPrice))
           // 保存完成后清空购物项
           settings.itemsToAdd.removeAll()
           print(settings.items)
       }label: {
           Text("Save")
       }
   }
   

3. 进入页面时重置购物项列表
   给NavigationStack添加onAppear修饰符，确保每次进入新建页面都是干净状态：

   NavigationStack {
       // 原Form内容
   }
   .onAppear {
       settings.itemsToAdd.removeAll()
   }
   .environmentObject(settings)
   

4. 移除无用状态变量
   删除CreateNewListing中未使用的adjustedBudget、newBudget变量，简化代码：

   struct CreateNewListing: View {
       @EnvironmentObject var settings: HomePageItem
       @State var storeName: String
       @State var budget: Float
       @State var itemName: String
       @State var itemPrice: String
       @State var boolValue = false
       
       // 剩余代码不变
   }
   

5. 同步修改预览和跳转参数
   更新预览代码：

   #Preview {
       CreateNewListing(storeName: "", budget: 0.00, itemName: "", itemPrice: "")
           .environmentObject(HomePageItem())
   }
   

   更新ContentView中的跳转参数：

   NavigationLink {
       CreateNewListing(storeName: "", budget: 0.00, itemName: "", itemPrice: "")
   } label: {
       Image(systemName: "plus")
           .foregroundColor(.orange)
           .font(.title3)
   }
   

额外优化建议 #

• NewList结构体中的item和itemPrice字段无实际意义，建议修改为关联完整购物项列表：

  struct NewList: Identifiable {
      var id = UUID()
      var storeName: String
      var budget: Float
      var items: [ItemToAdd]
  }
  

  保存时同步传入购物项列表：

  settings.items.append(NewList(storeName: storeName, budget: budget, items: settings.itemsToAdd))
  

内容的提问来源于stack exchange，提问作者Dan Fitzgerald