swift - Save JSON data to local file

Question

I get posts from Reddit API. I want to encode received JSON and write it to the local file. But after writing data to it, file is empty. Please advice how can I write encoded JSON data to the file or pretty JSON data.

class Utils {
        
        func saveToJSON() {
            
            UseCase().createPosts(sub: "ios", limit: 5, completion: { posts in
                print(posts)
                
                let filePath = self.getDocumentsDirectoryUrl().appendingPathComponent("landmarkData.json")
                print(filePath)
                
                do {
                    let jsonData = try JSONEncoder().encode(posts)
                    print(jsonData)
                    try jsonData.write(to: filePath)
                    // here landmarkData.json file is empty
                } catch {
                    print("Error writing to JSON file: \(error)")
                }
            })
        }
        
        func getDocumentsDirectoryUrl() -> URL {
            let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
            let documentsDirectory = paths[0]
            return documentsDirectory
        }
    }


struct RedditPost: Hashable, Codable, Identifiable {
            var username: String
            var createdHoursAgo: String
            var domain: String
            var title: String
            var text: String
            var imageURL: String
            var downs: Int
            var ups: Int
            var rating: Int { ups - downs }
            var comments: Int
            var saved: Bool = false
            var id: String
     }


class UseCase {
        func createPosts(sub: String, limit: Int, completion: (@escaping (_ data: [RedditPost]) -> Void)) {
            Repository().fillPostsArray(sub: sub, limit: limit) { (redditPosts: [RedditPost]) in
                DispatchQueue.main.async {
                    completion(redditPosts)
                }
            }
        }
}

user_1360730 · Answer

//Define globally..
let fileName = "landmarkData.json"


func saveToJSON() {
        
        UseCase().createPosts(sub: "ios", limit: 5, completion: { posts in
            print(posts)
            
            let filePath = self.getDocumentsDirectoryUrl().appendingPathComponent(fileName)
            print(filePath)
            
            do {
                let jsonData = try JSONEncoder().encode(posts)
                print(jsonData)
                try jsonData.write(to: filePath)
                // here landmarkData.json file is empty
            } catch {
                print("Error writing to JSON file: \(error)")
            }
        })
    }

Then while reading the file use the same constant...

func readFromJson() {

    let filePath = self.getDocumentsDirectoryUrl().appendingPathComponent(fileName)
    print(filePath)

    do {
        let jsonData = try JSONDecoder().decode(posts)
        print(jsonData)
     } catch {
         print("Error reading from JSON file: \(error)")
     }
}

user_7987502 · Answer

What I recommend is to use Codable objects, which means you can work in a more efficient and easier way to write/save json data files and load back to Codable objects.

Here is a small library that handles most of use cases with json files and data, its called CodableFiles. https://github.com/egzonpllana/CodableFiles

swift - Save JSON data to local file

2 Answers