Swift Firebase sending data inside a closure - swift

Question

I am trying to send data to another view controller. However, the data cannot be reached at the second view controller. Here is my code:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
super.prepare(for: segue, sender: sender)
switch(segue.identifier ?? "") {
case "tograddetail":
print("Going to Grad Detail")
guard let gradDetailViewController = segue.destination as? graduatedetailViewController else {
fatalError("Unexpected destination: \(segue.destination)")
}
guard let selectedgradCell = sender as? GradTableViewCell else {
fatalError("Unexpected sender: \(sender)")
}
guard let indexPath = tableView.indexPath(for: selectedgradCell) else {
fatalError("The selected cell is not being displayed by the table")
}
ref = FIRDatabase.database().reference().child("Database")
ref.observe(FIRDataEventType.value, with: { (snapshot) in
//print(snapshot.value)
if snapshot.exists() {
if let countdowntime = snapshot.value as? NSDictionary {
let selectedgrad = self.graduatename[indexPath.row]
if let graddata = countdowntime[selectedgrad] as? NSDictionary {
let theinstitution = graddata["Institution"] as! String
let thelocation = graddata["location"] as! String
let thetimeleft = graddata["timeleft"] as! Int
guard let firstgrad = graddetail(institution: theinstitution, location: thelocation, timeleft: thetimeleft) else {
fatalError("Unable to instantiate graddetail")
}
//print(firstgrad.institution)
//print(destinationgraddata.grad?.institution)
let destinationVC = segue.destination as! graduatedetailViewController
destinationVC.grad = firstgrad
}
}
}
})
default:
fatalError("Unexpected Segue Identifier; \(segue.identifier)")
}
}
And here is my code for the second view controller:
var grad: graddetail?
#IBOutlet weak var theinstitution: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
if let grad = grad {
theinstitution.text = grad.institution
}
}
However, the grad.institution value always return nil. Any idea?

Answer 1

The issue is observe(_:with:) is async and segue will called synchronously, so that when you get response in completion block of observe your segue is already performed.
To solved the issue what you need to do is call the observe before calling the performSegue and inside the completion block of observe when you get response call the perfromSegue with the value that you want to pass.