Why doesn't this SwiftUI View update when changing a #State variable? - swiftui

I've got a SwiftUI View that takes a Hacker News API submission ID, and then fetches the details for that item in fetchStory().
When fetchStory() completed its HTTP call, it updates the #State private var url on the View, however the View never re-renders to show the new value -- it always shows the initial empty value.
Why?
import Foundation
import SwiftUI
struct StoryItem: Decodable {
let title: String
let url: String?
}
struct StoryView: View {
public var _storyId: Int
#State private var url: String = "";
init(storyId: Int) {
self._storyId = storyId
self.fetchStory()
}
var body: some View {
VStack {
Text("(Load a webview here for the URL of Story #\(self._storyId))")
Text("URL is: \(self.url)") // this never changes!
}
}
private func fetchStory() {
let url = URL(string: "https://hacker-news.firebaseio.com/v0/item/\(self._storyId).json")!
let task = URLSession.shared.dataTask(with: url) {(data, response, error) in
guard let data = data else {
print(String(error.debugDescription))
return
}
do {
let item: StoryItem = try JSONDecoder().decode(StoryItem.self, from: data)
if let storyUrl = item.url {
self.url = storyUrl
} else {
print("No url")
}
} catch {
print(error)
}
}
task.resume()
}
}
struct StoryView_Previews: PreviewProvider {
static var previews: some View {
StoryView(storyId: 22862053)
}
}

something like this:
import SwiftUI
struct StoryItem: Decodable {
let title: String
let url: String?
}
class ObservedStoryId: ObservableObject {
#Published var storyId: String = ""
init(storyId: String) {
self.storyId = storyId
}
}
struct StoryView: View {
#ObservedObject var storyId: ObservedStoryId
#State var url: String = ""
var body: some View {
VStack {
Text("(Load a webview here for the URL of Story #\(self.storyId.storyId))")
Text("URL is: \(self.url)")
Text(self.storyId.storyId)
}.onReceive(storyId.$storyId) { _ in self.fetchStory() }
}
private func fetchStory() {
let url = URL(string: "https://hacker-news.firebaseio.com/v0/item/\(self.storyId.storyId).json")!
let task = URLSession.shared.dataTask(with: url) {(data, response, error) in
guard let data = data else {
print(String(error.debugDescription))
return
}
do {
let item: StoryItem = try JSONDecoder().decode(StoryItem.self, from: data)
if let storyUrl = item.url {
self.url = storyUrl
} else {
print("No url")
}
} catch {
print(error)
}
}
task.resume()
}
}
and call it like this:
struct ContentView: View {
#ObservedObject var storyId = ObservedStoryId(storyId: "22862053")
var body: some View {
StoryView(storyId: storyId)
}
}

to fix your problem:
init(storyId: Int) {
self._storyId = storyId
}
var body: some View {
VStack {
Text("(Load a webview here for the URL of Story #\(self._storyId))")
Text("URL is: \(self.url)") // this now works
}.onAppear(perform: fetchStory)
}
why does this works and not your code,
my guess is this: "self.url" can only be updated/changed within the special SwiftUI View functions, such as onAppear(), elsewhere it does not change a thing.

Related

Cant view the list of devices

I have a json-result that I get from my own "api". In this I have a list of different devices, that I like to view in a list.
When I add the ForEach, then I get the following error:
Generic struct 'List' requires that 'some AccessibilityRotorContent' conform to 'View'
The JsonResponse:
[{"name":"Tormek-T8","topHorizontal":55,"topVertical":55,"frontHorizontal":44,"frontVertical":44},{"name":"SH-332","topHorizontal":77,"topVertical":77,"frontHorizontal":88,"frontVertical":88}]
Can it be, that there are numbers in this JSON-String and not all is a String?
In my very simple code I had made a struct for the single Device and try to pull it from the url. Why I would get this error? Because the response of the JSON is not nil.
struct Device: Hashable, Codable {
let name: String
let topHorizontal: Double
let topVertical: Double
let frontHorizontal: Double
let frontVertical: Double
}
class ViewModel: ObservableObject {
#Published var devices: [Device] = []
func fetch() {
guard let url = URL(string: "https://cdn.rowoco.de/grindcalculator/devices") else {
return
}
let task = URLSession.shared.dataTask(with: url) { [weak self] data, _, error in
guard let data = data, error == nil else {
return
}
do {
let devices = try JSONDecoder().decode([Device].self, from: data)
DispatchQueue.main.async {
self?.devices = devices
}
} catch {
print(error)
}
}
task.resume()
}
}
struct CdnDevicesListView: View {
#Environment(\.presentationMode) var presentationMode
#StateObject var viewModel = ViewModel()
var body: some View {
NavigationView {
List {
ForEach(viewModel.devices, id: \.self) { device in
device.name
}
}
.navigationTitle("cdn devices")
.onAppear {
viewModel.fetch()
}
}
}
}
ForEach's content needs to be a View.
device.name is not a View.

SwiftUI Object details on list click

Building a crystal app. Displaying a list, showing details on click.
Been looking into ObservableObject, Binding, etc.
Tried #State in CrystalView but got lost pretty quickly.
What's the easiest way to pass data around views? Watched a few videos, still confused.
How do I pass crystals[key] into CrystalView()?
struct ContentView: View {
#State private var crystals = [String:Crystal]()
var body: some View {
Text("Crystals").font(.largeTitle)
NavigationView {
List {
ForEach(Array(crystals.keys), id:\.self) { key in
HStack {
NavigationLink(destination: CrystalView()) {
Text(key)
}
}
}
}.onAppear(perform:loadData)
}
}
func loadData() {
guard let url = URL(string: "https://lit-castle-74820.herokuapp.com/api/crystals") else { return }
URLSession.shared.dataTask(with: url) { data, _, error in
guard let data = data else { return }
do {
let decoded = try JSONDecoder().decode([String:Crystal].self, from: data)
DispatchQueue.main.async {
print(decoded)
self.crystals = decoded
}
} catch let jsonError as NSError {
print("JSON decode failed: \(jsonError)")
}
}.resume()
}
}
struct Crystal: Codable, Identifiable {
var id = UUID()
let composition, formation, colour: String
let metaphysical: [String]
}
struct CrystalView: View {
var body: some View {
Text("crystal")
}
}
try this approach, works well for me:
struct Crystal: Codable, Identifiable {
var id = UUID()
let composition, formation, colour: String
let metaphysical: [String]
// -- here, no `id`
enum CodingKeys: String, CodingKey {
case composition,formation,colour,metaphysical
}
}
struct CrystalView: View {
#State var crystal: Crystal? // <-- here
var body: some View {
Text("\(crystal?.composition ?? "no data")")
}
}
struct ContentView: View {
#State private var crystals = [String:Crystal]()
var body: some View {
Text("Crystals").font(.largeTitle)
NavigationView {
List {
ForEach(Array(crystals.keys), id:\.self) { key in
HStack {
NavigationLink(destination: CrystalView(crystal: crystals[key])) { // <-- here
Text(key)
}
}
}
}.onAppear(perform: loadData)
}
}
func loadData() {
guard let url = URL(string: "https://lit-castle-74820.herokuapp.com/api/crystals") else { return }
URLSession.shared.dataTask(with: url) { data, _, error in
guard let data = data else { return }
do {
let decoded = try JSONDecoder().decode([String:Crystal].self, from: data)
DispatchQueue.main.async {
print("decoded: \(decoded)")
self.crystals = decoded
}
} catch let jsonError as NSError {
print("JSON decode failed: \(jsonError)")
}
}.resume()
}
}
Something like this:
struct ContentView: View {
#State private var crystals: [Crystal] = []
var body: some View {
NavigationView {
List {
ForEach(crystals) { crystal in
NavigationLink(destination: CrystalView(crystal: crystal)) {
Text(crystal.name)
}
}
}
.navigationTitle("Crystals")
// initial detail view
Text("Select a crystal")
}
.task {
crystals = try? await fetchCrystals()
}
}
func fetchCrystals() async throws -> [Crystal] {
let (data, _) = try await URLSession.shared.data(from: "https://lit-castle-74820.herokuapp.com/api/crystals")
let decoder = JSONDecoder()
return try decoder.decode([Crystal].self, from: data) // you might want to convert this downloaded struct into a more suitable struct for the app.
}
}
struct CrystalView: View {
let crystal: Crystal
var body: some View {
Text(crystal.composition)
.navigationTitle(crystal.name)
}
}

#EnvironmentVariable not being passed to child views

I have 2 views - which I want to navigate between, and have a viewModel object shared between them as an EnvironmentObject. I keep getting the "A View.environmentObject(_:) for TidesViewModel may be missing as an ancestor of this view." error - but none of the solutions I have found seem to work. Please find below my code. The following is the first view:
import SwiftUI
struct ContentView: View {
#ObservedObject var tidesViewModel: TidesViewModel = TidesViewModel()
var body: some View {
NavigationView
{
List
{
ForEach (tidesViewModel.stations.indices) {
stationid in
HStack
{
NavigationLink(destination: TideDataView(stationId: tidesViewModel.stations[stationid].properties.Id))
{
Text(tidesViewModel.stations[stationid].properties.Name)
}
}
}
}
}.environmentObject(tidesViewModel)
}
}
and below is the child view - which throws the error.
import SwiftUI
struct TideDataView: View {
#EnvironmentObject var tidesViewModel : TidesViewModel
var stationId: String
init(stationId: String) {
self.stationId = stationId
getTidesForStation(stationId: stationId)
}
var body: some View {
List
{
ForEach (tidesViewModel.tides.indices)
{
tideIndex in
Text(tidesViewModel.tides[tideIndex].EventType)
}
}
}
func getTidesForStation(stationId: String)
{
tidesViewModel.getTidalData(forStation: stationId)
}
}
For completeness - below is the Observable object being passed:
import Foundation
import SwiftUI
class TidesViewModel: ObservableObject
{
private var tideModel: TideModel = TideModel()
var currentStation: Feature?
init()
{
readStations()
}
var stations: [Feature]
{
tideModel.features
}
var tides: [TidalEvent]
{
tideModel.tides
}
func readStations()
{
let stationsData = readLocalFile(forName: "stations")
parseStations(jsonData: stationsData!)
}
private func readLocalFile(forName name: String) -> Data? {
do {
if let bundlePath = Bundle.main.path(forResource: name,
ofType: "json"),
let jsonData = try String(contentsOfFile: bundlePath).data(using: .utf8) {
return jsonData
}
} catch {
print(error)
}
return nil
}
private func parseStations(jsonData: Data) {
do {
let decodedData: FeatureCollection = try JSONDecoder().decode(FeatureCollection.self,
from: jsonData)
//print(decodedData)
tideModel.features = decodedData.features
} catch let jsonError as NSError{
print(jsonError.userInfo)
}
}
func getTidalData(forStation stationId: String)
{
let token = "f43c068141bb417fb88909be5f68781b"
guard let url = URL(string: "https://admiraltyapi.azure-api.net/uktidalapi/api/V1/Stations/" + stationId + "/TidalEvents") else {
fatalError("Invalid URL")
}
var request = URLRequest(url: url)
request.httpMethod = "GET"
request.setValue(token, forHTTPHeaderField: "Ocp-Apim-Subscription-Key")
URLSession.shared.dataTask(with: request) { data, response, error in
guard let data = data else{ return }
do{
let decoder = JSONDecoder()
decoder.dataDecodingStrategy = .base64
let decodedData = try decoder.decode([TidalEvent].self, from: data)
DispatchQueue.main.async {
self.tideModel.tides = decodedData
}
}catch let error{
print(error)
}
}.resume()
}
}
You need to attach the modifier .environmentObject() directly to the view that will receive it. So, in your case, attach it to TideDataView, not to the NavigationView around it.
Your code would look like this:
NavigationLink {
TideDataView(stationId: tidesViewModel.stations[stationid].properties.Id)
.environmentObject(tidesViewModel)
} label: {
Text(tidesViewModel.stations[stationid].properties.Name)
}
// Delete the modifier .environmentObject() attached to the NavigationView

How to use data from 1 tab view to another tab view in Swiftui? Looking for a approach

I have 2 tabs and the associated views are tabAView and tabBView.
On tabAView, 1 API call is there and got user object which is Published object in its ViewModel. ViewModel name is UserViewModel. UserViewModel is being observed by tabAView.
On tabBView, I have to use that user object. Because on some actions, user object value is changed, those changes should be reflected on subsequent views.
I am confused about the environment object usage here. Please suggest what will be the best approach.
Here is the code to understand better my problem.
struct ContentView: View {
enum AppPage: Int {
case TabA=0, TabB=1
}
#StateObject var settings = Settings()
var viewModel: UserViewModel
var body: some View {
NavigationView {
TabView(selection: $settings.tabItem) {
TabAView(viewModel: viewModel)
.tabItem {
Text("TabA")
}
.tag(AppPage.TabA)
AppsView()
.tabItem {
Text("Apps")
}
.tag(AppPage.TabB)
}
.accentColor(.white)
.edgesIgnoringSafeArea(.top)
.onAppear(perform: {
settings.tabItem = .TabA
})
.navigationBarTitleDisplayMode(.inline)
}
.environmentObject(settings)
}
}
This is TabAView:
struct TabAView: View {
#ObservedObject var viewModel: UserViewModel
#EnvironmentObject var settings: Settings
init(viewModel: UserViewModel) {
self.viewModel = viewModel
}
var body: some View {
Vstack {
/// code
}
.onAppear(perform: {
/// code
})
.environmentObject(settings)
}
}
This is the UserViewModel where API is hit and user object comes:
class UserViewModel: ObservableObject {
private var apiService = APIService.shared
#Published var user: EndUserData?
init () {
getUserProfile()
}
func getUserProfile() {
apiService.getUserAccount() { user in
DispatchQueue.main.async {
self.user = user
}
}
}
}
Below is the APIService function, where the user object is saved into UserDefaults for use. Which I know is incorrect.(That is why I am looking for another solution). Hiding the URL, because of its confidential.
func getUserAccount(completion: #escaping (EndUserData?) -> Void) {
self.apiManager.makeRequest(toURL: url, withHttpMethod: .get) { results in
guard let response = results.response else { return completion(nil) }
if response.httpStatusCode == 200 {
guard let data = results.data else { return completion(nil) }
do {
let str = String(decoding: data, as: UTF8.self)
print(str)
let decoder = JSONDecoder()
let responseData = try decoder.decode(ResponseData<EndUserData>.self, from: data)
UserDefaults.standard.set(data, forKey: "Account")
completion(responseData.data)
} catch let jsonError as NSError {
print(jsonError.localizedDescription)
return completion(nil)
}
}
}
}
This is another TabBView:
struct TabBView: View {
var user: EndUserData?
init() {
do {
guard let data = UserDefaults.standard.data(forKey: "Account") else {
return
}
let decoder = JSONDecoder()
let responseData = try decoder.decode(ResponseData<EndUserData>.self, from: data)
user = responseData.data
} catch let jsonError as NSError {
print(jsonError.localizedDescription)
}
}
var body: some View {
VStack (spacing: 10) {
UserSearch()
}
}
}
This is another view in TabBView, where the User object is used. Changes are not reflecting here.
struct UserSearch: View {
private var user: EndUserData?
init(comingFromAppsSection: Bool) {
do {
guard let data = UserDefaults.standard.data(forKey: "Account") else {
return
}
let decoder = JSONDecoder()
let responseData = try decoder.decode(ResponseData<EndUserData>.self, from: data)
user = responseData.data
} catch let jsonError as NSError {
print(jsonError.localizedDescription)
}
}
var body: some View {
Vstack {
Text(user.status)
}
}
}
I have removed most of the code from a confidential point of view but this code will explain the reason and error. Please look into the code and help me.

Cannot get view to update with downloaded JSON

I am stuck at the simplest place right now.. I'm making a network request and just want the view to be updated once the JSON is received..
And I verified that:
JSON is valid
Valid response received (verified in print statement)
I've done this about 50 times and don't know why I'm stuck at this point.
struct ContentView: View {
#StateObject var nm = NetworkManager()
var body: some View {
VStack {
ScrollView {
HStack {
ForEach(nm.articles, id: \.hashValue) { article in
Text("Hello")
}
}.task {
do {
try await NetworkManager().getAllArticles(for: "mario")
} catch { print(error) }
}
}
Spacer()
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
import SwiftUI
final class NetworkManager: ObservableObject {
#Published var newsItem: News?
#Published var articles: [Article] = []
private let apiKey = ""//removed
private var baseUrlString: String {
"https://newsapi.org/v2/"
}
func getAllArticles(for searchItem: String) async throws {
let url = URL(string: baseUrlString + "everything?q=\(searchItem)&apiKey=\(apiKey)")!
let (data, _) = try await URLSession.shared.data(from: url)
let news = try JSONDecoder().decode(News.self, from: data)
DispatchQueue.main.async {
self.newsItem = news
self.articles = self.newsItem!.articles
}
}
}
struct News: Codable {
var totalResults: Int?
let articles: [Article]
}
struct Article: Codable, Hashable {
let author: String?
let title: String
let description: String
let url: String
let urlToImage: String?
let publishedAt: String
let content: String
}
Edit: removed apiKey
getAllArticles() is view-related, which means you should probably implement this function inside the View instead of ObservableObject.
struct ContentView: View {
#StateObject var nm = NetworkManager()
var body: some View {
VStack {
ScrollView {
VStack {
ForEach(nm.articles, id: \.hashValue) { article in
Text("Hello")
}
}.task {
do {
try await getAllArticles(for: "mario")
} catch { print(error) }
}
}
Spacer()
}
.frame(maxWidth: .infinity, maxHeight: .infinity)
}
}
extension ContentView {
func getAllArticles(for searchItem: String) async throws {
let url = URL(string: nm.baseUrlString + "everything?q=\(searchItem)&apiKey=\(NetworkManager.apiKey)")!
let (data, _) = try await URLSession.shared.data(from: url)
let news = try JSONDecoder().decode(News.self, from: data)
// Not necessary
// DispatchQueue.main.async {
nm.newsItem = news
nm.articles = nm.newsItem!.articles
// }
}
}
final class NetworkManager: ObservableObject {
#Published var newsItem: News?
#Published var articles: [Article] = []
static let apiKey = "YOUR_API_KEY"
var baseUrlString: String {
"https://newsapi.org/v2/"
}
}