How to send api response to UIViewController using Combine - ios

Question

I am updating my collectionView with a response from my api using Combine to provide real time info. My api returns NSArray which is working but for some strange reasons inside my SearchAPI class I can receive the response and print it out in the console print("Our array ", searchArray) but can't sink to my UIViewController and update my collectionView accordingly. print("value ", value) Value is always empty
import Foundation
import Combine
class SearchAPI {
static let shared = SearchAPI()
func fetchData(url: String, category: String, queryString: String) -> Future<NSArray, Error>{
var searchArray: NSArray = []
let urlString = url
print("url come ", urlString)
guard let url = URL(string: urlString) else {
fatalError()
}
var request = URLRequest(url: url)
request.setValue("application/json", forHTTPHeaderField: "Accept")
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpMethod = "GET"
let task = URLSession.shared.dataTask(with: request) { [weak self] data, response, error in
guard let data = data, error == nil else {
return
}
do{
let json = try? JSONSerialization.jsonObject(with: data, options: []) as? NSArray
if let responseJson = json {
searchArray = responseJson
print("Our array", searchArray)
}
}
}
task.resume()
return Future { promixe in
DispatchQueue.main.async {
promixe(.success(searchArray))
}
}
}
}
//In my UIViewController
var observers: [AnyCancellable] = []
let action = PassthroughSubject<NSArray, Never>()
var category = "tv"
var queryString = ""
private var models: NSArray = []
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
if isMovieSelected {
btnMoviesBottomBorder.backgroundColor = .secondaryPink
btnAlbumsBottomBorder.backgroundColor = .systemGray
btnAlbumsBottomBorder.backgroundColor = .systemGray
}
txtSearch.searchTextField.addTarget(self, action: #selector(searchItem), for: .editingChanged)
}
#objc func searchItem(){
moviesView.alpha = 0
albumsView.alpha = 0
booksView.alpha = 0
lblSrchResults.alpha = 1
queryString = txtSearch.text!.replacingOccurrences(of: " ", with: "%20")
print("who is calling ", queryString)
let url = "https://endpoint?category=\(category)&query=\(queryString)"
SearchAPI.shared.fetchData(url: url, category: category, queryString: queryString)
.receive(on: DispatchQueue.main)
.sink(receiveCompletion: { completion in
switch completion {
case .finished:
print("finished")
case .failure(let error):
print(error)
}
}, receiveValue: { [weak self] value in
print("value ", value)
self?.models = value
self?.searchCollectionView!.reloadData()
}).store(in: &observers)
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print("Fetched ", models.count)
return models.count
}

Answer 1

In your fetchData function, you create a dataTask to run the URL request. At some point later on that dataTask will complete and return an array.
Then you create a Future and send some code off to run on the main queue. That code has nothing inside of it to make it wait until the dataTask completes.
The code inside the Future is going to run "right away" and complete before a value has been assigned to searchArray.
You need to change your Future so that it only resolves (only completes) after the dataTask is done. Just tweaking your code a bit it looks something like:
func fetchData(url: String, category: String, queryString: String) -> Future<NSArray, Error>
{
return Future { promixe in
var searchArray: NSArray = []
let urlString = url
print("url come ", urlString)
guard let url = URL(string: urlString) else {
fatalError()
}
var request = URLRequest(url: url)
request.setValue("application/json", forHTTPHeaderField: "Accept")
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpMethod = "GET"
let task = URLSession.shared.dataTask(with: request) { data, response, error in
guard let data,
error == nil else {
promixe(.failure(error!))
return
}
do{
let json = try? JSONSerialization.jsonObject(with: data, options: []) as? NSArray
if let responseJson = json {
searchArray = responseJson
print("Our array", searchArray)
promixe(.success(searchArray))
}
}
}
task.resume()
}
}
I typed this into a playground, but I did not run it, so additional changes may be necessary.
All of the action now happens inside the future. Once you are in a future block then you should call its resolution function (in your code called promixe) for all success or failure cases.
I changed your code so that promixe is called ONLY when the data task completes (successfully or unsuccessfully).
For your code you should probably also:
Be sure to call proximate, once, on every path through your Futures block. In particular you need to catch the error that JSONSerialization might give you and called promixe to report the error. Otherwise your future may not complete if data comes back from the server, but it cannot be parsed.
Change your code to use Swift style JSON instead of using JSONSerialization that way you will have an [SomeType] instead of NSArray. Use the type system to your advantage to reduce the possibility of errors.
Instead of doing queryString = txtSearch.text!.replacingOccurrences(of: " ", with: "%20") use
txtSearch.text!.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed). It will cover more cases if the user types
something unexpected.