在URLSession.shared.dataTask和ViewController之间共享数据

Question

I am having problem sharing data between URLSession.shared.dataTask and the ViewController class. I am using a DispatchQueue and seems to work well when storing directly to label , however, when I try to store information to local fields this approach is not working.

This is my current code:

class ViewController: UITableViewController {

    var plantManager: PlantManager!

    override func viewDidLoad() {
        super.viewDidLoad()
        getPlantData()
        print("Info To Print:" + plantManager.getExtTemp())
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }


    func getPlantData(){
        let session = URLSession.shared
        let urlPath = PlantURL().getFullURL()
        let url = NSURL(string: urlPath)!
        print(url)
        let request = NSURLRequest(url: url as URL)
        let dataTask = session.dataTask(with: request as URLRequest) { (data:Data?, response:URLResponse?, error:Error?) -> Void in do{
            if let jsonResult = try JSONSerialization.jsonObject(with: data!, options: []) as? [[String:Any]],
                let dict = jsonResult.first {
                DispatchQueue.main.sync(execute: {
                    self.plantManager = PlantManager(intTemp: (dict["ExternalTemperature"] as? String)!, moist: (dict["SoilMoisture"] as? String)!, humidity: (dict["AmbientHumidity"] as? String)!, extTemp: (dict["ExternalTemperature"] as? String)!)
                })

            }else{
                print("No Parsing Correctly")
            }

        }catch let error as NSError{
            print(error.localizedDescription)
            }
            print("done, error: \(error)")
        }
        dataTask.resume()
    }
}

The plantManager field is nil and obviously, I can't access the is getter plantManager.getExtTemp() . I am new using Swift and I can't understand why this approach works to write to labels but does not when using fields.

Really appreciate a hand. Thank you in advance.

Answer 1

dataTask works asynchronously, use a completion handler:

Declare the method

func getPlantData(completion: ()->()) {

and replace

DispatchQueue.main.sync(execute: {
   self.plantManager = PlantManager(intTemp: (dict["ExternalTemperature"] as? String)!, moist: (dict["SoilMoisture"] as? String)!, humidity: (dict["AmbientHumidity"] as? String)!, extTemp: (dict["ExternalTemperature"] as? String)!)
})

with

DispatchQueue.main.async {
   self.plantManager = PlantManager(intTemp: dict["ExternalTemperature"] as! String, moist: dict["SoilMoisture"] as! String, humidity: dict["AmbientHumidity"] as! String, extTemp: dict["ExternalTemperature"] as! String)
   completion()
}

and call it in viewDidLoad

getPlantData() { 
    print("Info To Print:" + plantManager.getExtTemp())
}