文件被拒绝访问

我在写android应用，需要将json写入。txt文件。.txt文件位于项目根目录

解析json如下

string url2 = "http://new.murakami.ua/?mkapi=getProducts";
JsonValue json = await FetchAsync(url2);
private async Task<JsonValue> FetchAsync(string url)
{
    // Create an HTTP web request using the URL:
    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(new Uri(url));
    request.ContentType = "application/json";
    request.Method = "GET";
    // Send the request to the server and wait for the response:
    using (WebResponse response = await request.GetResponseAsync())
    {
        // Get a stream representation of the HTTP web response:
        using (Stream stream = response.GetResponseStream())
        {
            // Use this stream to build a JSON document object:
            JsonValue jsonDoc = await Task.Run(() => JsonObject.Load(stream));
            //dynamic data = JObject.Parse(jsonDoc[15].ToString);
            Console.Out.WriteLine("Response: {0}", jsonDoc.ToString());
            // Return the JSON document:
            return jsonDoc;
        }

我试着用这个:

StreamWriter sw = new StreamWriter(@"'myfile.txt");
sw.Write(json.ToString());
sw.Close();

但是上面写着System.UnauthorizedAccessException: Access to the path "/'myfile.txt" is denied.

如何解析json文件?

string path = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
string filename = System.IO.Path.Combine(path, "myfile.txt");
using (var streamWriter = new StreamWriter(filename, true))
{
    //Write your data here
}