[英]Why is my @AppStorage not working on SwiftUI?
我正在尝试在我的项目中设置 @AppStorage 包装器。
我正在从 JSON API(请参阅 DataModel)中提取文本,并希望将结果存储在 UserDefautls 中。 我希望获取数据。OnAppear 并将其存储到@AppStorage 中。 当用户点击“获取下一个文本”时,我想要获取一首新诗,并使用最新的文本数据更新@AppStorage,(这将删除过去存储的诗)。
目前,下面的代码构建但不在Text(currentPoemTitle)
中显示任何内容。
数据 Model
import Foundation
struct Poem: Codable, Hashable {
let title, author: String
let lines: [String]
let linecount: String
}
public class FetchPoem: ObservableObject {
// 1.
@Published var poems = [Poem]()
init() {
getPoem()
}
func getPoem() {
let url = URL(string: "https://poetrydb.org/random/1")!
// 2.
URLSession.shared.dataTask(with: url) {(data, response, error) in
do {
if let poemData = data {
// 3.
let decodedData = try JSONDecoder().decode([Poem].self, from: poemData)
DispatchQueue.main.async {
self.poems = decodedData
}
} else {
print("No data")
}
} catch {
print("Error")
}
}.resume()
}
}
测试视图
import SwiftUI
struct Test: View {
@ObservedObject var fetch = FetchPoem()
@AppStorage("currentPoemtTitle") var currentPoemTitle = ""
@AppStorage("currentPoemAuthor") var currentPoemAuthor = ""
var body: some View {
VStack{
Text(currentPoemTitle)
Button("Fetch next text") {
fetch.getPoem()
}
}.onAppear{
if let poem = fetch.poems.first {
currentPoemTitle = "\(poem.title)"
currentPoemAuthor = "\(poem.author)"
}
}
}
}
struct Test_Previews: PreviewProvider {
static var previews: some View {
Test()
}
}
我错过了什么? 谢谢。
这里有一些代码编辑可以帮助您前进。
我添加了 AppStorageKeys 来管理 @AppStorage 键,以避免重新键入键字符串时出错(即“currentPoemtTitle”)
您的问题询问如何使用数据更新@AppStorage,简单的解决方案是在 FetchPoem class 中添加 @AppStorage 变量,并在下载数据后在 FetchPoem class 中设置它们。 这也避免了需要.onAppear function。
使用@ObservedObject 的目的是能够使您的View 与数据保持同步。 通过添加额外的@AppStorage 层,您使@ObservedObject 变得毫无意义。 在视图中,我添加了一个 Text() 来直接使用 @ObservedObject 值显示标题,而不是依赖于 @AppStorage。 我不确定你是否想要这个,但它会完全消除对 @AppStorage 变量的需要。
我还使用 Combine 添加了一个 getPoems2() function,这是 Apple 用于下载异步数据的新框架。 它使代码更简单/更高效...... getPoems() 和 getPoems2() 都工作并做同样的事情:)
代码:
import Foundation
import SwiftUI
import Combine
struct AppStorageKeys {
static let poemTitle = "current_poem_title"
static let poemAuthor = "current_poem_author"
}
struct Poem: Codable, Hashable {
let title, author: String
let lines: [String]
let linecount: String
}
public class FetchPoem: ObservableObject {
@Published var poems = [Poem]()
@AppStorage(AppStorageKeys.poemTitle) var poemTitle = ""
@AppStorage(AppStorageKeys.poemAuthor) var poemAuthor = ""
init() {
getPoem2()
}
func getPoem() {
let url = URL(string: "https://poetrydb.org/random/1")!
URLSession.shared.dataTask(with: url) {(data, response, error) in
do {
guard let poemData = data else {
print("No data")
return
}
let decodedData = try JSONDecoder().decode([Poem].self, from: poemData)
DispatchQueue.main.async {
self.poems = decodedData
self.updateFirstPoem()
}
} catch {
print("Error")
}
}
.resume()
}
func getPoem2() {
let url = URL(string: "https://poetrydb.org/random/1")!
URLSession.shared.dataTaskPublisher(for: url)
// fetch on background thread
.subscribe(on: DispatchQueue.global(qos: .background))
// recieve response on main thread
.receive(on: DispatchQueue.main)
// ensure there is data
.tryMap { (data, response) in
guard
let httpResponse = response as? HTTPURLResponse,
httpResponse.statusCode == 200 else {
throw URLError(.badServerResponse)
}
return data
}
// decode JSON data to [Poem]
.decode(type: [Poem].self, decoder: JSONDecoder())
// Handle results
.sink { (result) in
// will return success or failure
print("poetry fetch completion: \(result)")
} receiveValue: { (value) in
// if success, will return [Poem]
// here you can update your view
self.poems = value
self.updateFirstPoem()
}
// After recieving response, the URLSession is no longer needed & we can cancel the publisher
.cancel()
}
func updateFirstPoem() {
if let firstPoem = self.poems.first {
self.poemTitle = firstPoem.title
self.poemAuthor = firstPoem.author
}
}
}
struct Test: View {
@ObservedObject var fetch = FetchPoem()
@AppStorage(AppStorageKeys.poemTitle) var currentPoemTitle = ""
@AppStorage(AppStorageKeys.poemAuthor) var currentPoemAuthor = ""
var body: some View {
VStack(spacing: 10){
Text("App Storage:")
Text(currentPoemTitle)
Text(currentPoemAuthor)
Divider()
Text("Observed Object:")
Text(fetch.poems.first?.title ?? "")
Text(fetch.poems.first?.author ?? "")
Button("Fetch next text") {
fetch.getPoem()
}
}
}
}
struct Test_Previews: PreviewProvider {
static var previews: some View {
Test()
}
}
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