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我是 SwiftUI 的新手，我尝试创建一个应用程序，它有一个目标列表，在列表上方，有一个添加按钮可以添加目标并将其显示在列表中。目前，我无法将目标实例添加到目标（目标数组）中，在创建视图中，我尝试将新的目标实例附加到我在另一个视图中创建的目标中。它给了我一条错误消息：Cannot use mutating member on immutable value: 'self' is immutable 在行 goals.append(Goal(...)) 上谁知道怎么修它？这是我的代码！非常感谢！
struct ContentVIEw: VIEw {
var goals: [Goal] = []
var body: some VIEw {
TabVIEw{
vstack{
Text("You have")
Text("0")
Text("tasks to do")
}.tabItem { Text("Home")}
MyScroll(1..<100).tabItem { Text("My Goals") }
}
}
}
struct MyScroll: VIEw {
var numRange: Range<Int>
var goals: [Goal]
init (_ r:Range<Int>) {
numRange = r
goals = []
}
var body: some VIEw {
NavigationVIEw{
vstack{
Navigationlink(destination: AddVIEw(goals:self.goals)){
Image(systemname: "folder.badge.plus")
}
List(goals) { goal in
HStack(alignment: .center){
Text(goal.name)
}
}
}
}.navigationTitle(Text("1111"))
}
}
struct AddVIEw: VIEw {
var goals:[Goal]
@State var types = ["study","workout","hobby","habbit"]
@State private var selected = false
@State var selection = Set<String>()
@State var goalname: String = ""
@State var goalType: String = ""
@State var isLongTerm: Bool = false
@State var progress: [Progress] = []
var body: some VIEw {
vstack{
Text("Create your goal")
// type in name
HStack{
TextFIEld("name",text: $goalname)
}.padding()
// choose type: a selection List
HStack{
List(types,ID: \.self,selection: $selection) {
Text($0)
}
.navigationbarItems(trailing: Editbutton())
}.padding()
// toggle if it is a logn term goal
HStack{
Toggle(isOn: $selected) {
Text("Is your goal Long Term (no end date)")
}.padding()
}.padding()
button(action: {
addGoal(goalname,goalType,isLongTerm,progress)
},label: {
/*@START_MENU_TOKEN@*/Text("button")/*@END_MENU_TOKEN@*/
})
}
}
// function that add the goal instance to the goals
mutating func addGoal( _ t:String,_ n:String,_ iLT: Bool,_ p: [Progress]){
let item: Goal = Goal(t,n,iLT,[])
goals.append(item)
}
}
目标只是我为存储信息而创建的结构：
import Foundation
// This is the structure for each goal when it is created
struct Goal: IDentifiable {
var ID: UUID
var type: String // type of goals
var name: String // the custom name of the goal
var isLongTerm: Bool // if goal is a long term goal (no deadline)
var progress: [Progress] // an array of progress for each day
init(_ t:String,_ p: [Progress]) {
ID = UUID()
type = t
name = n
isLongTerm = iLT
progress = p
}
}
实现此目的的一种方法是使用 @Binding 将 @State 保存在父视图中，并将其向下传递到视图层次结构，让子视图向上发送数据。
（一个警告是，在当前版本的 SwiftUI 中，通过多个视图发送 Binding 看起来可能会产生意想不到的结果，但一两个级别似乎没问题。另一种选择是使用带有 @Published 属性的 ObservableObject在视图之间传递）
注意 ContentView 如何拥有 [Goal]，然后后续子视图将其作为 @Binding 获取——$ 符号用于通过参数：
struct Goal: Identifiable {
var id: UUID
var type: String // type of goals
var name: String // the custom name of the goal
var isLongTerm: Bool // if goal is a long term goal (no deadline)
var progress: [Progress] // an array of progress for each day
init(_ t:String,_ n:String,_ iLT: Bool,_ p: [Progress]) {
id = UUID()
type = t
name = n
isLongTerm = iLT
progress = p
}
}
struct ContentView: View {
@State var goals: [Goal] = []
var body: some View {
TabView{
VStack{
Text("You have")
Text("\(goals.count)")
Text("tasks to do")
}.tabItem { Text("Home")}
MyScroll(numRange: 1..<100,goals: $goals).tabItem { Text("My Goals") }
}
}
}
struct MyScroll: View {
var numRange: Range<Int>
@Binding var goals: [Goal]
var body: some View {
NavigationView{
VStack{
NavigationLink(destination: AddView(goals:$goals)){
Image(systemName: "folder.badge.plus")
}
List(goals) { goal in
HStack(alignment: .center){
Text(goal.name)
}
}
}
}.navigationTitle(Text("1111"))
}
}
struct AddView: View {
@Binding var goals:[Goal]
@State var types = ["study","workout","hobby","habbit"]
@State private var selected = false
@State var selection = Set<String>()
@State var goalName: String = ""
@State var goalType: String = ""
@State var isLongTerm: Bool = false
@State var progress: [Progress] = []
var body: some View {
VStack{
Text("Create your goal")
// type in name
HStack{
TextField("Name",text: $goalName)
}.padding()
// choose type: a selection list
HStack{
List(types,id: \.self,selection: $selection) {
Text($0)
}
.navigationBarItems(trailing: EditButton())
}.padding()
// toggle if it is a logn term goal
HStack{
Toggle(isOn: $selected) {
Text("Is your goal Long Term (no end date)")
}.padding()
}.padding()
Button(action: {
addGoal(goalType,goalName,isLongTerm,progress)
},label: {
/*@START_MENU_TOKEN@*/Text("Button")/*@END_MENU_TOKEN@*/
})
}
}
// function that add the goal instance to the goals
func addGoal( _ t:String,_ p: [Progress]){
let item: Goal = Goal(t,n,iLT,[])
goals.append(item)
}
}
您的 addGoal 函数不再需要改变，因为它实际上不再改变自己的状态（无论如何这在 SwiftUI 中不起作用）。
作为旁注，我会谨慎地编写您的初始化程序和函数，就像您对 _ 未命名参数所做的那样——我在您的原始代码中找到了一个您打算传递名称的地方目标，而是传递该参数的类型，并且由于所有参数都未命名，因此没有警告。
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