SwiftUI从视图中操作结构中的项

Question

我希望能够编辑用户添加的"费用"并将其放入新视图中。在添加了新费用后，我在访问数据时遇到了问题。我可以删除项目并添加它们，但我想点击"费用"并查看和编辑其中的内容视图的图像

//内容视图

import SwiftUI
struct ExpenseItem: Identifiable, Codable {
let id = UUID()
let name: String
let type: String
let amount: Int
}
class Expenses: ObservableObject {
@Published var items = [ExpenseItem]() {
didSet {
let encoder = JSONEncoder()

if let encoded = try?
encoder.encode(items) {
UserDefaults.standard.set(encoded, forKey: "Items")
}
}
}
init() {
if let items = UserDefaults.standard.data(forKey: "Items") {
let decoder = JSONDecoder()

if let decoded = try?
decoder.decode([ExpenseItem].self, from: items) {
self.items = decoded
return
}
}
}
// Computed property that calculates the total amount
var total: Int {
self.items.reduce(0) { result, item -> Int in
result + item.amount
}
}
}
struct ContentView: View {
@ObservedObject var expenses = Expenses()
@State private var showingAddExpense = false
var body: some View {
NavigationView {
List {
ForEach(expenses.items) { item in
HStack {
VStack {
Text(item.name)
.font(.headline)
Text(item.type)
}

Spacer()
Text("$(item.amount)")
}
}
.onDelete(perform: removeItems)

// View that shows the total amount of the expenses
HStack {
Text("Total")
Spacer()
Text("(expenses.total)")
}
}
.navigationBarTitle("iExpense")
.navigationBarItems(trailing: Button(action: {
self.showingAddExpense = true
}) {
Image(systemName: "plus")
}
)
.sheet(isPresented: $showingAddExpense) {
AddView(expenses: self.expenses)
}
}
}
func removeItems(at offsets: IndexSet) {
expenses.items.remove(atOffsets: offsets)
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}

//AddExpense

import SwiftUI
struct AddView: View {
@Environment(.presentationMode) var presentationMode
@ObservedObject var expenses: Expenses
@State private var name = ""
@State private var type = "Personal"
@State private var amount = ""
static let types = ["Business", "Personal"]
var body: some View {
NavigationView {
Form {
TextField("Name", text: $name)

Picker("Type", selection: $type) {
ForEach(Self.types, id: .self) {
Text($0)
}
}

TextField("Amount", text: $amount)
.keyboardType(.numberPad)
}
.navigationBarTitle("Add new expense")
.navigationBarItems(trailing: Button("Save") {
if let actualAmount = Int(self.amount) {
let item = ExpenseItem(name: self.name, type: self.type, amount: actualAmount)
self.expenses.items.append(item)
self.presentationMode
.wrappedValue.dismiss()
}
})
}
}
}
struct AddView_Previews: PreviewProvider {
static var previews: some View {
AddView(expenses: Expenses())
}
}

Answer 1

删除AddView中的@observedObject。

视图无法更改ObservableObject。ObservableObject用于在值更改时得到通知。当您将开支类传递给AddView时，您就是在给它一个引用。因此，AddView可以更改开支，从而更新ContentView。