How to load a JSON tableView and save data even on dismiss? - ios

Question

I currently have a button that opens a TableViewController and loads the data using JSON like the following:
private func JSON() {
print(facility)
guard let url = URL(string: "https://example/example/example"),
let sample = value1.addingPercentEncoding(withAllowedCharacters: .urlQueryValueAllowed)
else { return }
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.httpBody = "example1=\(example)".data(using: .utf8)
URLSession.shared.dataTask(with: request) { data, _, error in
guard let data = data else { return }
do {
self.JStruct = try JSONDecoder().decode([exampleStruct].self,from:data)
DispatchQueue.main.async {
self.tableView.reloadData()
}
}
catch {
print(error)
}
}.resume()
}
Then after I am done looking at the tableview I close it by doing:
self.dismiss(animated: true, completion: nil)
using a BarButtonItem.
The issue is every time the UIView opens it takes some time to load the data. Is there anyway to have the tableView load just once and when dismissed and re-opened just have the same data show that was already loaded before?

Answer 1

The best thing you can do is to store the data locally. Either use a local database or a plain text file to store the data. When you open the page check whether data is already present. If it is already present load it, and call the API in background silently to update the existing data. If data is not saved, call the API, load the data and save it locally.
func getFileURL() -> URL {
let fileName = "CacheData"
let documentDirURL = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
let fileURL = documentDirURL.appendingPathComponent(fileName).appendingPathExtension("json")
return fileURL
}
func createFile(data: Data) {
let fileURL = getFileURL()
do {
try data.write(to: fileURL)
} catch let e {
print(e.localizedDescription)
}
}
func loadData() -> Data? {
let fileURL = getFileURL()
do {
let data = try Data(contentsOf: fileURL)
return data
} catch let e {
print(e.localizedDescription)
}
return nil
}
In your viewDidLoad method do something like:
let fileURL = getFileURL()
if FileManager.default.fileExists(atPath: fileURL.path) {
if let data = loadData() {
do {
self.JStruct = try
JSONDecoder().decode([exampleStruct].self,from:data)
DispatchQueue.main.async {
self.tableView.reloadData()
} catch {
print(error)
}
}
}
JSON()
And call the createFile when you get data from the API. You may need to write the file and load the file using a background queue to avoid overloading and freezing of your main thread.