onDelete：在删除之前从条目访问数据

问题描述

当用户滑动删除列表中的条目时，是不是有一个指针可以用来获取被删除条目的信息？在删除条目之前，我想知道类别总数。我遇到了函数 removeItems 的问题，它给出了错误：无法将“IndexSet”类型的值转换为预期的参数类型“Int”

struct CatItem:  Codable,Identifiable {
    var id = UUID()
    var catNum: Int       
    var catName: String
    var catTotal: Double
    var catPix: String
    var catShow: Bool 
}

class Categories: ObservableObject {
    
    @Published var catItem: [CatItem] {
    didSet {
         }
     }
 } 





struct manCatView: View {
    
    @EnvironmentObject var userData: UserData
    @EnvironmentObject var categories: Categories
    
    var pic: String = ""
    
    var body: some View {
        
        List {
            ForEach(0 ..< categories.catItem.count) { index in
                if index.catShow == true {
                HStack {
                    let pic = categories.catItem[index].catPix
                    Image(systemName: pic)
                        .resizable()
                        
                        .foregroundColor(Color(colors[index]))
                        .frame(width: 40,height: 40)
                    
                    Text(categories.catItem[index].catName)
                    }
                }
            }
            .onDelete(perform: removeItems) 
        }
        .navigationBarTitle(Text("Manage Categories"),displayMode: .inline)
        NavigationLink(destination: addCatView()) {Text("Add Categories")
            .fontWeight(.bold)}
            .font(.title2)
            .disabled(categories.catItem.count > 16)
            
            .padding([.leading,.trailing],10)
            .accentColor(Color(red: 60/255,green: 160/255,blue: 240/255))
        
        Text("")
        Text("")
        Text("Add Up to 5 Categories")
        Text("Swipe Left to Delete a Category")
        
        Rectangle()
            .frame(width: 50,height: 175)
            .foregroundColor(.white)
    }
    
    
    func removeItems(at offsets: IndexSet) {
        var catTotal: Double = 0.0
        
        //subtract entry amount from category total
        catTotal = categories.catItem[offsets].catTotal  // <-- need help with index here
        userData.totalArray[grandTotal] -= catTotal
        userData.totalArray[userTotal] -= catTotal
        
        
        categories.catItem.remove(atOffsets: offsets)
    }
}

解决方法

这里的IndexSet 是一个简单的Indexies 集合，在简单的情况下它只包含一个元素（用户滑动一个一个地删除条目）。因此，为简单起见，您可以为此使用 .first 元素。但更好 - 遍历完整集，它会让你有更多的控制。

因此您需要的代码可能类似于：

func removeItems(at offsets: IndexSet) {
    var catTotal: Double = 0.0
    
    offsets.forEach { singleOffset in
        //subtract entry amount from category total
        catTotal = categories.catItem[singleOffset].catTotal
        userData.totalArray[grandTotal] -= catTotal
        userData.totalArray[userTotal] -= catTotal
    }
    
    categories.catItem.remove(atOffsets: offsets)
}