FileWork

public static async Task WriteToFile(string key, string foldername, string filename)
        {
            // Get the text data from the textbox. 
            byte[] fileBytes = System.Text.Encoding.UTF8.GetBytes(key.ToCharArray());
            // Get the local folder.
            StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;
            // Create a new folder name DataFolder.
            var dataFolder = await local.CreateFolderAsync(Path.Combine("DataFolder", foldername), CreationCollisionOption.OpenIfExists);
            // Create a new file named DataFile.txt.
            var file = await dataFolder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
            // Write the data from the textbox.
            using (var s = await file.OpenStreamForWriteAsync())
            {
                s.Write(fileBytes, 0, fileBytes.Length);
            }
        }
        
public static async Task<string> ReadFile(string foldername, string filename)
        {
            // Get the local folder.
            StorageFolder local = Windows.Storage.ApplicationData.Current.LocalFolder;

            if (local != null)
            {
                Stream file = null;
                // Get the DataFolder folder.
                var dataFolder = await local.GetFolderAsync(Path.Combine("DataFolder", foldername));
                // Get the file.
                file = await dataFolder.OpenStreamForReadAsync(filename);
                string key;
                // Read the data.
                using (StreamReader streamReader = new StreamReader(file))
                {
                    return key = streamReader.ReadToEnd();
                }
            }
            else
                return null;
        }