Unable to extract data from Observable Object - ios

Question

I'm trying to display data from an observed object.
Initially I tried to keep it simple, to merely display one member of a struct: 'base' (value: "stations").
struct Sample: Codable {
let coord: Coord
let weather: [Weather]
let base: String
let main: Main
let visibility: Int
let wind: Wind
let clouds: Clouds
let dt: Double
// let sys: Sys
let id: Int
let name: String
// let cod: Int
}
I did some defensive coding with '?' but I got the following compiler error:
So I replaced the '?' with '!', knowing that I should have some data.
I find this frustrating, coming from an imperative-paradigm background.
What am I doing wrong?
Here's the data dump:
Sample(coord: DataTaskPubTab.Coord(lon: -0.13, lat: 51.51), weather:
[DataTaskPubTab.Weather(id: 300, main: "Drizzle", description: "light
intensity drizzle")], base: "stations", main:
DataTaskPubTab.Main(temp: 280.32, pressure: 1012, humidity: 81,
tempMin: 279.15, tempMax: 281.15), visibility: 10000, wind:
DataTaskPubTab.Wind(speed: 4.1, deg: 80), clouds:
DataTaskPubTab.Clouds(all: 90), dt: 1485789600.0, id: 2643743, name:
"London")
Here's the Observable Object:
class StandardWeatherReportLoader: ObservableObject {
#Published var networkMessage: String?
#Published var hasAlert = false
#Published var weatherReport: Sample?
#Published var hasReport = false
func doStandard() {
let url = EndPoint.weather.path()
var request = URLRequest(url: EndPoint.weather.path()!)
request.httpMethod = "GET"
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
let task = URLSession.shared.dataTask(with: url!) { (data: Data?, _: URLResponse?, error: Error?) -> Void in
DispatchQueue.main.async {
guard error == nil else {
self.networkMessage = error?.localizedDescription
self.hasAlert = true
return
}
do {
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let result = try decoder.decode(Sample.self, from: data!)
self.weatherReport = result
self.hasReport = true
print(result)
} catch let error as NSError {
print(error)
}
}
}
task.resume()
}
}

Answer 1

Apparently this works:
struct StandardWeatherView: View {
#EnvironmentObject var settings: Settings
#ObservedObject var standardWeatherReportLoader = StandardWeatherReportLoader()
init() {
self.standardWeatherReportLoader.doStandard()
}
var body: some View {
NavigationView {
ZStack {
Color("FernGreen").edgesIgnoringSafeArea(.all)
VStack {
if standardWeatherReportLoader.weatherReport?.base == nil {
Text("Sorry, NO data.")
} else {
Text(standardWeatherReportLoader.weatherReport!.base)
}
Text(/*#START_MENU_TOKEN#*/"Hello, World!"/*#END_MENU_TOKEN#*/)
}
.navigationBarTitle(Text("Weather Report"), displayMode: .inline)
}.alert(isPresented: $standardWeatherReportLoader.hasAlert, content: { () -> Alert in
Alert(title: Text(verbatim: standardWeatherReportLoader.networkMessage!))
})
}
}
}

Answer 2

Very probably the web services data is not yet available when the view renders for the first time. So you shouldn't force unwrap the value with !. If you want to create a Text() element in both cases, you can simply use the ?? operation (see Nil-Coalescing Operator in the Swift language documentation):
Text(standardWeatherReportLoader.weatherReport?.base ?? "Sorry, NO data.")