Using a completion handler in another class/extension - ios

Question

I have a class, LocationViewController, which needs to implement a TableView. I have a function getParsedTestingLocation() which uses a completion handler from another function to get some data.
class LocationViewController: UIViewController {
#IBOutlet weak var tableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
tableView.delegate = self
tableView.dataSource = self
}
func getParsedTestingLocations(completion: #escaping ([TestingLocation]?, Error?) -> (Void)) {
getTestingLocationsJSON(completion: { testLocationsJSON, error in
if let testLocationsJSON = testLocationsJSON {
let testLocationsData = Data(testLocationsJSON.utf8)
let decoder = JSONDecoder()
do {
let testLocations = try decoder.decode([TestingLocation].self, from: testLocationsData)
completion(testLocations, nil)
} catch {
print(error)
}
}
})
}
}
I want to use the value testLocations within getParsedTestingLocations() in an external extension in this file. Here are the extensions I have:
extension LocationViewController: UITableViewDelegate {
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
print("you tapped me!")
}
}
extension LocationViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 0
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
cell.textLabel?.text = "empty cell"
return cell
}
}
Within all 3 tableView() functions I want to get the values stored in testLocations in the completion handler in these functions. How could I do this?

Answer 1

Actually you don't need a completion handler. Reload the table view inside the completion closure of the API call
class LocationViewController: UIViewController {
#IBOutlet weak var tableView: UITableView!
var locationData = [TestingLocation]()
override func viewDidLoad() {
super.viewDidLoad()
tableView.delegate = self
tableView.dataSource = self
getParsedTestingLocations()
}
func getParsedTestingLocations() {
getTestingLocationsJSON(completion: { testLocationsJSON, error in
if let testLocationsJSON = testLocationsJSON {
let testLocationsData = Data(testLocationsJSON.utf8)
let decoder = JSONDecoder()
do {
self.locationData = try decoder.decode([TestingLocation].self, from: testLocationsData)
DispatchQueue.main.async {
self.tableView.reloadData()
}
} catch {
print(error)
}
}
})
}
}
extension LocationViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return locationData.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
let location = locationData[indexPath.row]
cell.textLabel?.text = location.whatEverStringYouWantToDisplay
return cell
}
}
Replace whatEverStringYouWantToDisplay with the real struct member name.

Answer 2

You don't need a completionHandler in getParsedTestingLocations in this case as the function already calls a function which has completionHandler. Just use a variable
class LocationViewController: UIViewController {
private lazy var locationArr = [TestingLocation]()
#IBOutlet weak var tableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
tableView.delegate = self
tableView.dataSource = self
getParsedTestingLocations()
}
func getParsedTestingLocations() {
getTestingLocationsJSON(completion: { testLocationsJSON, error in
if let testLocationsJSON = testLocationsJSON {
let testLocationsData = Data(testLocationsJSON.utf8)
let decoder = JSONDecoder()
do {
let testLocations = try decoder.decode([TestingLocation].self, from: testLocationsData)
self.locationArr = testLocations
DispatchQueue.main.async {
self.tableView.reloadData()
}
} catch let error {
//Show Alert
}
}
})
}
}
extension LocationViewController: UITableViewDelegate, UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return locationArr.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
cell.textLabel?.text = locationArr[indexPath.row].variable
return cell
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
print("you tapped me! \(locationArr[indexPath.row])")
}
}