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[英]Passing the data from one view to another SwiftUI via NavigationLink
[英]SwiftUI: Checkmarks disappear when changing from one view to another using NavigationLink
我正在尝试制作一个应用程序,该应用程序根据单击的 NavigationLink 显示带有选择/复选标记的列表。 我遇到的问题是,当我 go 返回主视图然后我再次在 NavigationLink 中 go 时,我的选择消失了。 我正在尝试在 UserDefaults 中保存切换值,但它没有按预期工作。 下面我将粘贴详细的主要内容视图。
第二种观点:
struct CheckView: View {
@State var isChecked:Bool = false
@EnvironmentObject var numofitems: NumOfItems
var title:String
var count: Int=0
var body: some View {
HStack{
ScrollView {
Toggle("\(title)", isOn: $isChecked)
.toggleStyle(CheckToggleStyle())
.tint(.mint)
.onChange(of: isChecked) { value in
if isChecked {
numofitems.num += 1
print(value)
} else{
numofitems.num -= 1
}
UserDefaults.standard.set(self.isChecked, forKey: "locationToggle")
}.onTapGesture {
}
.onAppear {
self.isChecked = UserDefaults.standard.bool(forKey: "locationToggle")
}
Spacer()
}.frame(maxWidth: .infinity,alignment: .topLeading)
}
}
}
主视图:
struct CheckListView: View {
@State private var menu = Bundle.main.decode([ItemsSection].self, from: "items.json")
var body: some View {
NavigationView{
List{
ForEach(menu){
section in
NavigationLink(section.name) {
VStack{
ScrollView{
ForEach(section.items) { item in
CheckView( title: item.name)
}
}
}
}
}
}
}.navigationBarHidden(true)
.navigationViewStyle(StackNavigationViewStyle())
.listStyle(GroupedListStyle())
.navigationViewStyle(StackNavigationViewStyle())
}
}
物品栏目:
[
{
"id": "9DC6D7CB-B8E6-4654-BAFE-E89ED7B0AF94",
"name": "Africa",
"items": [
{
"id": "59B88932-EBDD-4CFE-AE8B-D47358856B93",
"name": "Algeria"
},
{
"id": "E124AA01-B66F-42D0-B09C-B248624AD228",
"name": "Angola"
}
Model:
struct ItemsSection: Codable, Identifiable, Hashable {
var id: UUID = UUID()
var name: String
var items: [CountriesItem]
}
struct CountriesItem: Codable, Equatable, Identifiable,Hashable {
var id: UUID = UUID()
var name: String
}
正如评论中已经提到的,我看不到您从 UserDefaults 中读取的位置,因此无论存储在那里,您都不会阅读它。 但即便如此,每个 Toggle 都使用相同的键,因此您正在覆盖该值。
我不使用仅在本地使用的@State var isChecked ,而是创建另一个结构项,该结构项从 json 获取标题,并包含一个 boolean 初始化为 false。
据我了解,我认为解决方案可能类似于以下代码。 只是几件事:
视图的代码:
//
// CheckItem.swift
// CheckItem
//
// Created by Sebastian on 24.08.22.
//
import SwiftUI
struct ContentView: View {
var body: some View {
VStack() {
CheckItemView()
}
}
}
struct CheckItemView: View {
let testStringForTestData: String = "Check Item Title"
@AppStorage("itemSections") var itemSections: [ItemSection] = []
func addCheckItem(title: String, numberOfItems: Int) {
var itemArray: [Item] = []
for i in 0...numberOfItems {
itemArray.append(Item(title: "item \(i)"))
}
itemSections.append(ItemSection(title: title, items: itemArray))
}
func getSelectedItemsCount() -> Int{
var i: Int = 0
for itemSection in itemSections {
let filteredItems = itemSection.items.filter { item in
return item.isOn
}
i = i + filteredItems.count
}
return i
}
var body: some View {
NavigationView{
VStack() {
List(){
ForEach(itemSections.indices, id: \.self){ id in
NavigationLink(destination: ItemSectionDetailedView(items: $itemSections[id].items)) {
Text(itemSections[id].title)
}
.padding()
}
}
Text("Number of checked items: \(self.getSelectedItemsCount())")
.padding()
Button(action: {
self.addCheckItem(title: testStringForTestData, numberOfItems: Int.random(in: 0..<4))
}) {
Text("Add Item")
}
.padding()
}
}
}
}
struct ItemSectionDetailedView: View {
@Binding var items: [Item]
var body: some View {
ScrollView() {
ForEach(items.indices, id: \.self){ id in
Toggle(items[id].title, isOn: $items[id].isOn)
.padding()
}
}
}
}
struct ItemSection: Identifiable, Hashable, Codable {
var id: String = UUID().uuidString
var title: String
var items: [Item]
}
struct Item: Identifiable, Hashable, Codable {
var id: String = UUID().uuidString
var title: String
var isOn: Bool = false
}
这里是使用@AppStorage 的调整:
extension Array: RawRepresentable where Element: Codable {
public init?(rawValue: String) {
guard let data = rawValue.data(using: .utf8),
let result = try? JSONDecoder().decode([Element].self, from: data)
else {
return nil
}
self = result
}
public var rawValue: String {
guard let data = try? JSONEncoder().encode(self),
let result = String(data: data, encoding: .utf8)
else {
return "[]"
}
return result
}
}
正如评论中所述,您必须将isChecked
属性与CountryItem
本身相关联。 为了让它工作,我改变了 model 并添加了一个isChecked
属性。 如果 JSON allread 存在,您需要手动将其添加到 JSON 中。
struct CheckView: View {
@EnvironmentObject var numofitems: NumOfItems
//use a binding here as we are going to manipulate the data coming from the parent
//and pass the complete item not only the name
@Binding var item: CountriesItem
var body: some View {
HStack{
ScrollView {
//use the name and the binding to the item itself
Toggle("\(item.name)", isOn: $item.isChecked)
.toggleStyle(.button)
.tint(.mint)
// you now need the observe the isChecked inside of the item
.onChange(of: item.isChecked) { value in
if value {
numofitems.num += 1
print(value)
} else{
numofitems.num -= 1
}
}.onTapGesture {
}
Spacer()
}.frame(maxWidth: .infinity,alignment: .topLeading)
}
}
}
struct CheckListView: View {
@State private var menu = Bundle.main.decode([ItemsSection].self, from: "items.json")
var body: some View {
NavigationView{
List{
ForEach($menu){ // from here on you have to pass a binding on to the decendent views
// mark the $ sign in front of the property name
$section in
NavigationLink(section.name) {
VStack{
ScrollView{
ForEach($section.items) { $item in
//Pass the complete item to the CheckView not only the name
CheckView(item: $item)
}
}
}
}
}
}
}.navigationBarHidden(true)
.navigationViewStyle(StackNavigationViewStyle())
.listStyle(GroupedListStyle())
.navigationViewStyle(StackNavigationViewStyle())
}
}
示例 JSON:
[
{
"id": "9DC6D7CB-B8E6-4654-BAFE-E89ED7B0AF94",
"name": "Africa",
"items": [
{
"id": "59B88932-EBDD-4CFE-AE8B-D47358856B93",
"name": "Algeria",
"isChecked": false
},
{
"id": "E124AA01-B66F-42D0-B09C-B248624AD228",
"name": "Angola",
"isChecked": false
}
]
}
]
使用 JSON 并将其存储在包中的方法将阻止您在应用程序启动之间保留isChecked
属性。 因为您不能从您的应用程序中写入 Bundle。 只要应用程序处于活动状态,该选择就会一直存在,但一旦您重新安装或强制退出它就会恢复默认设置。
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