Data not correctly getting populated in tableview sections - ios

Question

I am making an app in which I need this thing in one of the screens.
I have used the tableview with sections as shown in the code below
var sections = ["Adventure type"]
var categoriesList = [String]()
var items: [[String]] = []
override func viewDidLoad() {
super.viewDidLoad()
categoryTableView.delegate = self
categoryTableView.dataSource = self
Client.DataService?.getCategories(success: getCategorySuccess(list: ), error: getCategoryError(error: ))
}
func getCategorySuccess(list: [String])
{
categoriesList = list
let count = list.count
var prevInitial: Character? = nil
for categoryName in list {
let initial = categoryName.first
if initial != prevInitial { // We're starting a new letter
items.append([])
prevInitial = initial
}
items[items.endIndex - 1].append(categoryName)
}
for i in 0 ..< count
{
var tempItem = items[i]
let tempSubItem = tempItem[0]
let char = "\(tempSubItem.first)"
sections.append(char)
}
}
func getCategoryError(error: CError)
{
print(error.message)
}
func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
return self.sections[section]
}
func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return self.sections.count
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.items[section].count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = categoryTableView.dequeueReusableCell(withIdentifier: "tableCell", for: indexPath)
cell.textLabel?.text = self.items[indexPath.section][indexPath.row]
return cell
}
But it is producing runtime errors on return self.items[section].count
The reason for this error is because I am loading data (items array) is from server and then populating sections array after it. At the time when tableview gets generated, both the sections and items array is empty. That is why error occurs.
I am new to iOS and not getting grip over how to adjust data in sections of tableview.
Can someone suggest me a better way to do this?
What should be number of rows in section when I have no idea how much items server call will return?
Also i want to cover the case when server call fails and no data is returned. Would hiding the tableview (and showing error message) be enough?
Any help would be much appreciated.

Answer 1

See if this works: Make your data source an optional:
var items: [[String]]?
And instantiate it inside your getCategorySuccess and fill it with values. Afterwards call categoryTableView.reloadData() to reload your table view.
You can add a null check for your rows like this:
return self.items?[section].count ?? 0
This returns 0 as a default. Same goes for number of sections:
return self.items?.count ?? 0
In case the call fails I would show an error message using UIAlertController.

Answer 2

Your comment is incorrect: "At the time when tableview gets generated, both the sections and items array is empty. That is why error occurs."
According to your code, sections is initialized with one entry:
var sections = ["Adventure type"]
This is why your app crashes. You tell the tableview you have one section, but when it tries to find the items for that section, it crashes because items is empty.
Try initializing sections to an empty array:
var sections = [String]()
Already things should be better. Your app should not crash, although your table will be empty.
Now, at the end of getCategorySuccess, you need to reload your table to reflect the data retrieved by your service. Presumably, this is an async callback, so you will need to dispatch to the main queue to do so. This should work:
DispatchQueue.main.async {
self.categoryTableView.reloadData()
}