我正在学习 SwiftUI。我从做 Apple SwiftUI 教程开始。在其中一个中，他们提供了@EnviromentalObjects 来更改他们的模型，他们正在改变isFavorite bool 状态。但是他们没有将@ObservedObject 与 UserDefaults 一起使用，当我重新加载我的应用程序时，所有更改都令人失望。我已经学会了如何将UserDefaults用于视图中的值，现在如果我只想显示isFavorive对象或所有对象，并且当我重新加载我的应用程序时，这个切换按钮正在保存我的更改，我可以在我的对象列表中进行设置。
但我想对编辑我的模型做同样的事情。
有我的模型：
import SwiftUI
import CoreLocation
struct City: Hashable, Codable, Identifiable {
var id: Int
var country: String
var name: String
var description: String
fileprivate var imageName: String
fileprivate var coordinates: Coordinates
var state: String
var people: Int
var area: Int
var continent: Continent
var isFavorite: Bool
var isFeatured: Bool
var locationCoordinate: CLLocationCoordinate2D {
CLLocationCoordinate2D(
latitude: coordinates.latitude,
longitude: coordinates.longitude)
}
enum Continent: String, CaseIterable, Codable, Hashable {
case europe = "Europe"
case asia = "Asia"
case america = "America"
}
}
还有一个文件，我从 JSON 文件中加载数据（从苹果教程复制）
import UIKit
import SwiftUI
import CoreLocation
var CityData: [City] = load("CityData.json")
func load<T: Decodable>(_ filename: String) -> T {
let data: Data
guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
else {
fatalError("Couldn't find \(filename) in main bundle.")
}
do {
data = try Data(contentsOf: file)
} catch {
fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
}
do {
let decoder = JSONDecoder()
return try decoder.decode(T.self, from: data)
} catch {
fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
}
}
final class ImageStore {
typealias _ImageDictionary = [String: CGImage]
fileprivate var images: _ImageDictionary = [:]
fileprivate static var scale = 2
static var shared = ImageStore()
func image(name: String) -> Image {
let index = _guaranteeImage(name: name)
return Image(images.values[index], scale: CGFloat(ImageStore.scale), label: Text(verbatim: name))
}
static func loadImage(name: String) -> CGImage {
guard
let url = Bundle.main.url(forResource: name, withExtension: "jpg"),
let imageSource = CGImageSourceCreateWithURL(url as NSURL, nil),
let image = CGImageSourceCreateImageAtIndex(imageSource, 0, nil)
else {
fatalError("Couldn't load image \(name).jpg from main bundle.")
}
return image
}
fileprivate func _guaranteeImage(name: String) -> _ImageDictionary.Index {
if let index = images.index(forKey: name) { return index }
images[name] = ImageStore.loadImage(name: name)
return images.index(forKey: name)!
}
}
在这里你可以看到 CityData 是如何使用的：
**%% in UserData.swift file %%**
final class UserData: ObservableObject {
@Published var city = CityData
}
**%And in my view %%**
struct CityList: View {
@EnvironmentObject private var userData: UserData
@ObservedObject var SettingsVM = SettingsViewModel()
var body: some View {
NavigationView {
List {
Toggle(isOn: $SettingsVM.showFavoritesOnly) {
Text("Show Favorites Only")
}
ForEach(userData.city) { City in
if !self.SettingsVM.showFavoritesOnly || City.isFavorite {
NavigationLink(
destination: ContentView(city: City)
.environmentObject(self.userData)
)
{
CityRow(city: City)
}
}
}
}
.navigationBarTitle(Text("Capitals"))
}
}
}
%% 以及我如何更改“isFavorite”值
Button(action: {
self.userData.city[self.cityIndex].isFavorite.toggle();
print(String(self.city.isFavorite));
}) {
if self.userData.city[self.cityIndex].isFavorite {
Image(systemName: "star.fill")
.foregroundColor(Color.yellow)
} else {
Image(systemName: "star")
.foregroundColor(Color.gray)
}
}
我试图在 UserDefault.standard.object 中嵌入 CityData，但它没有用。我肯定做错了什么。你能帮助我吗？
