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iOS Build a Weather App with Swift (Retired) Data Modeling With Structures Swift Initializers

Ivan Dergachev
Ivan Dergachev
4,337 Points
Posted by Ivan Dergachev
Ivan Dergachev
4,337 Points

Initialization problem when trying to get Celsius value

Hi. Here in Russia we use metric system, so I'm trying to format the temperature properly before applying it to the label in the next few steps. I've wrote a small function to convert from Fahrenheit to Celsius.

func convertToCelsius(tempFahr: Int) -> Int {
        return (tempFahr - 32) * 5/9
    }

And I'm calling this function during initialisation.

        let tempFahrenheit = currentWeather["temperature"] as Int
        temperature = convertToCelsius(tempFahrenheit)

But Xcode gives me compiler errors no matter what I try.

"Variable 'self.temperature' used before being initialized"

Here's the full code

import Foundation
import UIKit

struct Current {

    var currentTime: String?
    var temperature: Int
    var humidity: Double
    var precipProbability: Double
    var summary: String
    var icon: UIImage?

    init(weatherDictionary: NSDictionary) {
        let currentWeather = weatherDictionary["currently"] as NSDictionary

        let tempFahrenheit = currentWeather["temperature"] as Int
        temperature = convertToCelsius(tempFahrenheit)

        humidity = currentWeather["humidity"] as Double
        precipProbability = currentWeather["precipProbability"] as Double
        summary = currentWeather["summary"] as String

        let currentTimeIntValue = currentWeather["time"] as Int
        currentTime = dateStringFromUnixTime(currentTimeIntValue)

        let iconString = currentWeather["icon"] as String
        icon = weatherIconFromString(iconString)


    }

    func dateStringFromUnixTime(unixTime: Int) -> String {
        let timeInSeconds = NSTimeInterval(unixTime)
        let weatherDate = NSDate(timeIntervalSince1970: timeInSeconds)
        let dateFormatter = NSDateFormatter()
        dateFormatter.timeStyle = .ShortStyle
        return dateFormatter.stringFromDate(weatherDate)

    }

    func weatherIconFromString(stringIcon: String) -> UIImage {
        var imageName: String

        switch stringIcon {

        case "clear-day":
            imageName = "clear-day"
        case "clear-night":
            imageName = "clear-night"
        case "rain":
            imageName = "rain"
        case "snow":
            imageName = "snow"
        case "sleet":
            imageName = "sleet"
        case "wind":
            imageName = "wind"
        case "fog":
            imageName = "fog"
        case "cloudy":
            imageName = "cloudy"
        case "partly-cloudy-day":
            imageName = "partly-cloudy"
        case "partly-cloudy-night":
            imageName = "cloudy-night"
        default:
            imageName = "default"
        }

        var iconImage = UIImage(named: imageName)
        return iconImage!
    }

    func convertToCelsius(tempFahr: Int) -> Int {
        return (tempFahr - 32) * 5/9
    }

}

2 Answers

dungeonkeeperhf
dungeonkeeperhf
3,272 Points
dungeonkeeperhf
dungeonkeeperhf
3,272 Points

You are trying to assign the conversion to 'temperature', temperature is not a variable, it's the value you get from the api, the value of temperature is stored in temp farenheight.

Do this instead:

let tempFahrenheit = currentWeather["temperature"] as Int

var newTemp = convertToCelsius(tempFahrenheit)

The value of newTemp is your converted temperature.

Ivan Dergachev
Ivan Dergachev
4,337 Points
Ivan Dergachev
Ivan Dergachev
4,337 Points

Hi! Thank you for the reply! But even this code gives me the same error.

So. This works OK:

    var currentTime: String?
    var temperature: Int
    var humidity: Double
    var precipProbability: Double
    var summary: String
    var icon: UIImage?

    init(weatherDictionary: NSDictionary) {
        let currentWeather = weatherDictionary["currently"] as NSDictionary

        temperature = currentWeather["temperature"] as Int

        humidity = currentWeather["humidity"] as Double
        precipProbability = currentWeather["precipProbability"] as Double
        summary = currentWeather["summary"] as String

        let currentTimeIntValue = currentWeather["time"] as Int
        currentTime = dateStringFromUnixTime(currentTimeIntValue)

        let iconString = currentWeather["icon"] as String
        icon = weatherIconFromString(iconString)


    }

As far as I understand, I declare the variables, then initialize the Foundation dictionary from the JSON dictionary that I received from the API, then fill the keys with the data of appropriate type.

In the example Pasan provided (with icon and weatherIconFromString) he's using exactly the same pattern I'm trying to mimic: processing dictionary data with the function and only then load it into variable that will be available later in the ViewEditor as currentWeather.temperature. But this (or what I provided in the original post) gives an initialization error. What am I doing wrong?

    var currentTime: String?
    var temperature: Int
    var humidity: Double
    var precipProbability: Double
    var summary: String
    var icon: UIImage?

    init(weatherDictionary: NSDictionary) {
        let currentWeather = weatherDictionary["currently"] as NSDictionary

        //temperature = currentWeather["temperature"] as Int
        let tempFahrenheit = currentWeather["temperature"] as Int
        var newTemp = convertToCelsius(tempFahrenheit)
        temperature = newTemp as Int

        humidity = currentWeather["humidity"] as Double
        precipProbability = currentWeather["precipProbability"] as Double
        summary = currentWeather["summary"] as String

        let currentTimeIntValue = currentWeather["time"] as Int
        currentTime = dateStringFromUnixTime(currentTimeIntValue)

        let iconString = currentWeather["icon"] as String
        icon = weatherIconFromString(iconString)


    }
Andrew Rodko
Andrew Rodko
27,881 Points
Andrew Rodko
Andrew Rodko
27,881 Points

You can't call a function within a struct until the variables have finished initializing. The solution would be to set your temperature as an optional (like Pasan did for currentTime)