image doesn't display after getting the link from firebase - ios

Question

I run a python script on my raspberry pi that takes a picture, moves it in the cloud and uploads the link to firebase.
Because the picture taking and uploading takes approximately 15 seconds I'm using DispatchQueue.main.asyncAfter.
In my current state, I'm able to take pictures whenever I want to, but there are 2 things I can't do.
How to be able to get the firebase element whenever a change happened. Python can do that, I don't know what the swift method for that.
The picture doesn't show. Is it because I want to display it from DispatchQueue.main.asyncAfter?
Thanks
import UIKit
import Firebase
import FirebaseDatabase
class RpiOps: UIViewController {
#IBOutlet weak var ivImage: UIImageView!
#IBOutlet weak var LblResult: UILabel!
#IBOutlet weak var tvLink: UITextView!
#IBAction func btn1Pic(_ sender: Any) {
rpi2do(state: "single_pic")
rpiResults(state: "-")
let actityIndicator = UIActivityIndicatorView(frame: CGRect(x: 0, y: 0, width: 50, height: 50))
actityIndicator.center = self.view.center
actityIndicator.hidesWhenStopped = true
actityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.gray
view.addSubview(actityIndicator)
actityIndicator.startAnimating()
UIApplication.shared.beginIgnoringInteractionEvents()
DispatchQueue.main.asyncAfter(deadline: .now() + 20) {
actityIndicator.stopAnimating()
UIApplication.shared.endIgnoringInteractionEvents()
let ref = Database.database().reference()
//let post : [String: AnyObject] = ["2do": state as AnyObject]
ref.child("rpi_results").observeSingleEvent(of: .value, with: { (snapshot) in
let ud = snapshot.value as! [String: Any]
let asa = ud["got"] as! String
self.tvLink.text = asa
print("asa:", asa)
//self.LblResult
let url = URL(string: asa)
let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
self.ivImage.image = UIImage(data: data!)
self.displayAlert(title: "Finished!", message: "Your picture has been taken. See the link here: " + asa)
//self.rpi2do(state: "-")
})
}
rpi2do(state: "-")
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
// rpi operation
func rpi2do(state: String) {
let ref = Database.database().reference()
let post : [String: AnyObject] = ["2do": state as AnyObject]
ref.child("rpi2do").setValue(post)
}
// rpi operation
func rpiResults(state: String) {
let ref = Database.database().reference()
let post : [String: AnyObject] = ["got": state as AnyObject]
ref.child("rpi_results").setValue(post)
}
func displayAlert(title: String, message: String) {
let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: { (action) in
self.dismiss(animated: true, completion: nil)
}))
self.present(alert, animated: true, completion: nil)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}

Answer 1

According to the Firebase docs, I think you've got the right method above in observeSingleElement to answer your first question. On the second one, make sure that you are getting the results of observeSingleEvent back onto the main thread before trying updating any UI elements, like below. You may be seeing the no change in the photo because you are not on the main thread after the database call.
ref.child("rpi_results").observeSingleEvent(of: .value, with: { (snapshot) in
let ud = snapshot.value as! [String: Any]
let asa = ud["got"] as! String
DispatchQueue.main.sync {
self.tvLink.text = asa
print("asa:", asa)
//self.LblResult
let url = URL(string: asa)
let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
self.ivImage.image = UIImage(data: data!)
self.displayAlert(title: "Finished!", message: "Your picture has been taken. See the link here: " + asa)
//self.rpi2do(state: "-")
}
})