Unable to update JSON data in cacheDirectory

it's been passed a week and I still couldn't figure out what am I missing in my code. I simply want to save the JSON file in my local cacheDirectory and load it back to the offline users. My code is able to save and read back from the local directory, but it doesn't work if I updated the JSON data from the GitHub repository. Only the original JSON data was loaded and the updated JSON file only loaded when I changed some codes and restart the simulator. Looks like there is no overwrite code to overwrite the existing JSON file.

Simply saying, I want to save the most updated JSON data in a local directory and load it back every time I made changes on the GitHub repository. For example, I tested it out with two slightly different JSON links by commenting out the two links alternatively to see the updated JSON. Please help me with what I can't figure out with my code. Thanks in advance. My code is below:

class FetchingJSONFile5 {
@Published var allSongs: [TuunoLabu] = []
@Published var isNewFile: Bool = true
let folderOne = "TuunoLabu_Folder1"
init() {
createFolderOne()
downloadJSON()
if let lyrics = fetchTuunoLabu(from: "TuunoLabu") {
allSongs = lyrics
}
}
private func createFolderOne() {
guard let directoryOne = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first?.appendingPathComponent(folderOne).relativePath else { return }
if !FileManager.default.fileExists(atPath: directoryOne) {
do {
try FileManager.default.createDirectory(atPath: directoryOne, withIntermediateDirectories: true)
print("Successfully created Folder One")
//print(directoryOne)
} catch let error {
print("Error while creating Folder One", error)
}
}
}
private func downloadJSON() {
guard let urlRequest = URL(string:
// This JSON has id 1 to 748
"https://raw.githubusercontent.com/siantung/TuunoLabu/fac87c9d6b63f5e52cadb8873fb0d77cd0fc91e1/JSON/TuunoLabu.json"
// This JSON has id 1 to 800
//"https://raw.githubusercontent.com/siantung/Hymn-iOS/main/HymnSong(02-25-2023).json"
)
else {
print("ERROR: Could not find the URL")
return
}
guard let directory = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask)
.first?.appendingPathComponent(folderOne)
.appendingPathComponent("TuunoLabu.json") else { return }
//print(directory)
let dataTask = URLSession.shared.dataTask(with: urlRequest) { [weak self] data, _, error in
guard let data = data, error == nil else { return }
do {
try data.write(to: directory, options: .atomic)
print("Successfully saved downloaded JSON new file.")
self?.isNewFile = true
} catch let error {
print("Error decoding: ",error)
self?.isNewFile = false
}
}
dataTask.resume()
}
private func fetchTuunoLabu(from name: String) -> [TuunoLabu]? {
guard let directoryOne = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask)
.first?.appendingPathComponent(folderOne)
.appendingPathComponent("TuunoLabu.json") else {
print("Error to retrieve directory while fetching file")
return nil
}
if FileManager.default.fileExists(atPath: directoryOne.relativePath) {
do {
let data = try Data(contentsOf: directoryOne)
return try JSONDecoder().decode([TuunoLabu].self, from: data)
} catch {
print("Error JSON decoding: \(error)")
}
}
return nil
}
}

It's a classic timing issue. The data is downloaded asynchronously, the result of fetchTuunoLabu is retrieved before the completion handler of the URLSession is being called.

With your code put the expression if let lyrics = ... into the completion handler after try data.write or use the data directly

However I recommend to take advantage of async/await and also of the error handling in Swift.

First of all replace createFolderOne with the following method. It returns the URL to the file by given filename in the caches directory and creates the directory on the fly if it doesn't exist. A possible error is thrown to the caller

private func cachedURL(fileName: String = "TuunoLabu.json") throws -> URL {
let directoryOne = try FileManager.default.url(for: .cachesDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
.appendingPathComponent(folderOne)
if !FileManager.default.fileExists(atPath: directoryOne.path) {
try FileManager.default.createDirectory(at: directoryOne, withIntermediateDirectories: true)
}
return directoryOne.appendingPathComponent(fileName)
}

The downloadJSON method can be reduced to these few lines

private func downloadJSON() async throws {
guard let url = URL(string:
"https://raw.githubusercontent.com/siantung/TuunoLabu/fac87c9d6b63f5e52cadb8873fb0d77cd0fc91e1/JSON/TuunoLabu.json") else {
throw URLError(.badURL)
}
let fileURL = try cachedURL()
let (data, _) = try await URLSession.shared.data(from: url)
try data.write(to: fileURL, options: .atomic)
isNewFile = true
}

Again, any error is thrown. The benefit of async is although the data is loaded asynchronously the method behaves like a synchronous method and awaits the result

The third method contains also a few lines

private func fetchTuunoLabu(from name: String) throws -> [TuunoLabu] {
let fileURL = try cachedURL(fileName: name)
let data = try Data(contentsOf: fileURL)
return try JSONDecoder().decode([TuunoLabu].self, from: data)
}

The rest of the class is

class FetchingJSONFile5 {
@Published var allSongs: [TuunoLabu] = []
@Published var isNewFile: Bool = true
let folderOne = "TuunoLabu_Folder1"
init() {
Task {
do {
try await downloadJSON()
allSongs = try fetchTuunoLabu(from: "TuunoLabu.json")
} catch {
isNewFile = false
print(error)
// or show something more significant to the user
}
}
}