在等待属性初始化的 init 中调用函数

Question

I have an Observable Object class to store a forecast object for my app

The class looks like this:

final class ForecastData: ObservableObject {
    @Published var forecast: DarkSkyResponse

    public func getForecast(at location: CLLocation) {
        let request = DarkSkyRequest(key: "KEYGOESHERE")
        let point = DarkSkyRequest.Point(location.coordinate.latitude, location.coordinate.longitude)

        guard let url = request.buildURL(point: point) else {
            //Handle this better
            preconditionFailure("Failed to construct URL")
        }

        let task = URLSession.shared.dataTask(with: url) {
            data, response, error in

            DispatchQueue.main.async {
                guard let data = data else {
                    //Handle this better
                    fatalError("No Data Recieved")
                }
                guard let forecast = DarkSkyResponse(data: data) else {
                    //Handle this better
                    fatalError("Decoding Failed")
                }
                self.forecast = forecast
            }
        }
        task.resume()
    }

    init() {
        self.getForecast(at: CLLocation(latitude: 37.334987, longitude: -122.009066))
    }
}

The first part simply generates a URL to access the API by. Then I start a URLSession which downloads the data and then parses it into a DarkSkyResponse object. Finally I set the @Published variable to the forecast object.

My problem is when I call the function in the initialiser, I get an error because the forecast property is not initialised. What is the best way to get around this? Where should I call the function? By the way I am using this class in my SwiftUI View using an @ObservedObject property wrapper

Answer 1

Case1: use optional (and you need to handle it in View)

@Published var forecast: DarkSkyResponse?

Case2: use some default instance

@Published var forecast = DarkSkyResponse()

Both variants are equivalent and acceptable, so just by your preference.

Answer 2

Try this changes:

@Published var forecast: DarkSkyResponse!

and

init() {
    super.init()
    self.getForecast(at: CLLocation(latitude: 37.334987, longitude: -122.009066))
}