UITableView with Segmented Controller not displaying data immediately - Swift - swift

Question

I have a Tab Bar Controller, and one of the two views from it is a TableViewController. The TableViewController has a SegmentedControl bar on the top of the table to switch between two datasets pulled from Firebase.
When I run the app, the table doesn't show any data straight away, only when I switch to the other segment of the SegmentControl bar. But, when I switch back, the data for the first segments loads.
I put in a breakpoint to see what was happening, and it was skipping over the code I wrote to pull the data from Firebase, so the arrays were empty upon initial loading, hence the lack of data. Yet, when I switch segments to the other option, the data appears.
I'm also trying to sort the data within the arrays, and this doesn't do anything at all because it runs when the arrays come back empty, so there is nothing to sort.
My code is:
class LeaderboardViewController: UITableViewController
{
#IBOutlet weak var segmentedControl: UISegmentedControl!
#IBOutlet var leaderboardTable: UITableView!
var countyRef = Database.database().reference().child("countyleaderboard")
var schoolRef = Database.database().reference().child("schoolleaderboard")
var refHandle: UInt!
var countyList = [County]()
var schoolList = [School]()
override func viewDidLoad()
{
super.viewDidLoad()
fetchData()
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int
{
var sectionCount = 0
switch(segmentedControl.selectedSegmentIndex)
{
case 0:
sectionCount = countyList.count
break
case 1:
sectionCount = schoolList.count
break
default:
break
}
return sectionCount
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
{
let boardCell = tableView.dequeueReusableCell(withIdentifier: "boardCell", for: indexPath)
switch(segmentedControl.selectedSegmentIndex)
{
case 0:
boardCell.textLabel!.text = "" + countyList[indexPath.row].name! + ": \(countyList[indexPath.row].score!)"
break
case 1:
boardCell.textLabel!.text = "" + schoolList[indexPath.row].name! + ": \(schoolList[indexPath.row].score!)"
break
default:
break
}
return boardCell
}
func fetchData()
{
schoolRef.observe(.childAdded, with:
{ snapshot in
if let dictionary = snapshot.value as? [String: AnyObject]
{
let school = School()
school.name = dictionary["name"] as! String
school.score = dictionary["score"] as! Float
self.schoolList.append(school)
}
}, withCancel: nil)
self.schoolList.sort(by: { $0.score > $1.score })
countyRef.observeSingleEvent(of: .value, with: { snapshot in
for child in snapshot.children
{
let snap = child as! DataSnapshot
let county = County()
county.name = snap.key as String
county.score = snap.value as! Float
self.countyList.append(county)
}
})
self.countyList.sort(by: { $0.score > $1.score })
DispatchQueue.main.async
{
self.leaderboardTable.reloadData()
}
}
#IBAction func segmentedControlChanged(_ sender: Any)
{
DispatchQueue.main.async
{
self.leaderboardTable.reloadData()
}
}
}
My questions are:
Why does the data not load straight away?
Where are the arrays coming from if they are not being populated with data on the first run? And why are they not being sorted if that code is directly below the code that populates them?

Answer 1

The dispatch block should be after the for loop and before the }).
It should be within the observe/observeSingleEvent. Also your sort code needs to be inside the same block. Like below:
countyRef.observeSingleEvent(of: .value, with: { snapshot in
for child in snapshot.children
{
let snap = child as! DataSnapshot
let county = County()
county.name = snap.key as String
county.score = snap.value as! Float
self.countyList.append(county)
}
self.countyList.sort(by: { $0.score > $1.score })
DispatchQueue.main.async
{
self.leaderboardTable.reloadData()
}
})