How to initialize data in Preview provider in SwiftUI - swift

Question

I am trying to fetch data from localhost, make a list of posts with List View and pass data to CustomDetailView. Here is my code for NetworkManager:
My ListView:
And StoryDetails View:
So what I have to pass to StoryDeatils_Preview?
Here is the StoryDetails code
import SwiftUI
struct StoryDetails: View {
var story: Story
var body: some View {
VStack(alignment: .leading) {
HStack {
Text("story #123456")
.font(.callout)
.foregroundColor(Color.gray)
Spacer()
Text("5 days ago")
.font(.callout)
.foregroundColor(Color.gray)
Button(action:{
print("Hello there")
}){
Image(systemName:"info.circle").resizable()
.frame(width:22.0, height:22.0)
.accentColor(Color.gray)
}
}
Text(story.body)
.foregroundColor(.black)
.kerning(1)
.lineLimit(nil)
HStack {
Button(action: {
print("Hello World")
}){
HStack {
Image(systemName:"heart")
.accentColor(.black)
Text("233")
.foregroundColor(.black)
}
.padding(.trailing)
HStack {
Image(systemName:"bubble.left")
.accentColor(.black)
Text("45")
.foregroundColor(.black)
}
}
}
}
}
}
struct StoryDetails_Previews: PreviewProvider {
static var previews: some View {
StoryDetails(
story: Story(
id: 1,
author: 1,
body: "Testing",
edited_time: "September 2019",
pub_date: "October 2018",
comments: [Comment](),
story_likes: [StoryLike]()
)
)
}
}
Error:

Answer 1

Hi there first I need to see the StoryDetails() but if StoryDetails a Story it should be declared inside as var story: Story let me explain more in example code:
Here you can see my network manager class:
class NetworkManager: ObservableObject {
let url: String = "https://jsonplaceholder.typicode.com/todos/1"
var objectWillChange = PassthroughSubject<NetworkManager, Never>()
init() {
fetchData()
}
#Published var user: User? {
didSet {
objectWillChange.send(self)
print("set user")
}
}
func fetchData() {
guard let url = URL(string: url) else {return}
print("fetch data")
URLSession.shared.dataTask(with: url) { (data, response, error) in
guard error == nil else {return}
print("no error")
guard let data = data else {return}
print("data is valid")
let user = try! JSONDecoder().decode(User.self, from: data)
DispatchQueue.main.async {
self.user = user
}
}.resume()
}
}
that's my content view where network manager is initialized inside:
struct ContentView: View {
#ObservedObject var networkManager = NetworkManager()
var body: some View {
VStack {
DetailsView(user: networkManager.user)
}
}
}
Details view struct holds user variable:
struct DetailsView: View {
var user: User?
var body: some View {
VStack {
Text("id: \(user?.id ?? 0)")
Text("UserID: \(user?.userId ?? 0 )")
Text("title: \(user?.title ?? "Empty")")
}
}
}
and that's the DetailsView as you can see inside of this struct I declared a user object of type User need to be pass it so if I want to show it in PreviewProvider it would be like the code below
struct DetailsView_Previews: PreviewProvider {
static var previews: some View {
DetailsView(user: User(id: 0, userId: 0, title: "hello", completed: false)
}
}
model:
struct User: Decodable {
var userId: Int = 0
var id: Int = 0
var title: String = ""
var completed: Bool = false
}
PS: For sure you can unwrap better than this way to provide
any nil exception it's just POC