Data Storage

The following implementation provides a simple way to read and write JSON files in the app's documents directory. This allows you to store app settings, user preferences, or any small amounts of data that need to persist between app launches.

Implementation

1. Create a Swift File
   • In Xcode, go to File > New > File From Template...
   • Select Swift File, name it FileHandler.swift, and paste the following code:

import Foundation

class FileHandler {

    // Initializes a FileManager instance to interact with the file system.
    let fileManager = FileManager.default

    // Writes the given 'text' to a file with the specified 'fileName'.
    func writeTextToFile(text: String, fileName: String) {
        let filePath = getFilePath(fileName: fileName)

        do {
            try text.write(to: filePath, atomically: true, encoding: .utf8)
        } catch {
            print("Error writing text to file: \(error.localizedDescription)")
        }
    }

    // Reads the text content from a file with the specified 'fileName' and returns it as an optional String.
    func readTextFromFile(fileName: String) -> String? {
        let filePath = getFilePath(fileName: fileName)

        do {
            let text = try String(contentsOf: filePath, encoding: .utf8)
            return text
        } catch {
            print("Error reading text from file: \(error.localizedDescription)")
            return nil
        }
    }

    // Constructs and returns the full file path URL for the given 'fileName' within the document directory.
    private func getFilePath(fileName: String) -> URL {
        let documentsDirectory = fileManager.urls(for: .documentDirectory, in: .userDomainMask).first!
        let filePath = documentsDirectory.appendingPathComponent(fileName)
        return filePath
    }
}

2. Integrate with Your View Controller
   • In MainViewController.swift, add methods to interact with the FileHandler class and expose them to JavaScript:

// Function to read data from app storage
@objc func readData(_ params: [String: String]) {
    var javaScript: String = ""
    let fileHandler = FileHandler()
    if let readData = fileHandler.readTextFromFile(fileName: params["fileName"] ?? "data.json") {
        if let successCallback = params["successCallback"] {
            javaScript = "\(successCallback)('\(readData)');"
            evaluateJavascript(javaScript: javaScript)
        }
    } else {
        if let errorCallback = params["errorCallback"] {
            javaScript = "\(errorCallback)(false);"
        }
        evaluateJavascript(javaScript: javaScript)
    }
}

// Function to write data into app storage
@objc func writeData(_ params: [String: String]) {
    var javaScript: String = ""
    if let content = params["content"] {
        let fileHandler = FileHandler()
        fileHandler.writeTextToFile(text: content, fileName: params["fileName"] ?? "data.json")
        if let successCallback = params["successCallback"] {
            javaScript = "\(successCallback)('true');"
        }
        evaluateJavascript(javaScript: javaScript)
    } else {
        if let errorCallback = params["errorCallback"] {
            javaScript = "\(errorCallback)(false);"
        }
        evaluateJavascript(javaScript: javaScript)
    }
}

3. Using the Storage in JavaScript
   • To save an object (session) as JSON, use the native writeData method:

// Object to be saved as JSON
let session = {
    foo: 'bar',
    fiz: 'baz'
}

// Write the session to the storage
enClose({
    nativeCall: 'writeData',
    data: {
        content: JSON.stringify(session)
    },
    errorCallback: 'console.error'
});

• To retrieve the stored data later, use readData along with a callback function (readDataCallback):

// Read data from storage and assign a callback
enClose({
    nativeCall: 'readData',
    successCallback: 'readDataCallback',
    errorCallback: 'console.log'
});

// Callback function to handle the read data
function readDataCallback(text) {
    session = JSON.parse(text);
    console.log(session);
}

This setup enables seamless data persistence between app launches, ensuring important settings and preferences are maintained.