Win Phone 8.1 : OutOfMemory Exception while downloading large files (30 MB) - windows-phone

Question

I am creating a universal Windows Phone 8.1 App. I am trying to download the file and view it into launcher. I works for small file less than 15 MB files. But when file size is more than 15 MB, I got the out of memory exception.
async private Task<object> GetMailAttachments(string attachNotify)
{
try
{
cmdBarMailItem.IsEnabled = false;
if (await Device.IsNetworkAvailable())
{
cts = new CancellationTokenSource();
// Ignore SSL Certificate which is untrusted,expired and has invalid hostname.
var filter = new HttpBaseProtocolFilter() { AllowUI = false };
filter.IgnorableServerCertificateErrors.Add(Windows.Security.Cryptography.Certificates.ChainValidationResult.Untrusted);
filter.IgnorableServerCertificateErrors.Add(Windows.Security.Cryptography.Certificates.ChainValidationResult.Expired);
filter.IgnorableServerCertificateErrors.Add(Windows.Security.Cryptography.Certificates.ChainValidationResult.InvalidName);
// Start calling the soap service #userGetAttachmentByIndex
using (var client = new System.Net.Http.HttpClient(new WinRtHttpClientHandler(filter)))
{
//Prepare parameters which is to be post via soap envelope.
List<KeyValuePair<string, string>> parameter = new List<KeyValuePair<string, string>>();
parameter.Add(new KeyValuePair<string, string>("sessionId", GlobalInfo.SessionID));
parameter.Add(new KeyValuePair<string, string>("attachmentIndex", attachNotify.Split('|')[1].ToString()));
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("text/xml"));
client.DefaultRequestHeaders.Add("SOAPAction", "userGetAttachmentByIndex");
var postContent = new StringContent(StringHelper.ConstructSoapRequest(parameter, "userGetAttachmentByIndex"), Encoding.UTF8, "text/xml");
// Getting response from soap service
var response = await client.PostAsync(new Uri(AppEnv.ServiceEndPoint), postContent, cts.Token);
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
string soapResponse = await response.Content.ReadAsStringAsync();
var soap = XDocument.Parse(soapResponse);
XNamespace ns = "http://service.webservice.cryoserver.ci";
var base64BinaryStr = soap.Descendants(ns + "userGetAttachmentByIndexResponse").First().Descendants(ns + "return").First().Descendants(ns + "attachmentType").First().Descendants(ns + "binaryData").First().Descendants(ns + "base64Binary").First().Value;
await saveStringToLocalFile(base64BinaryStr);
var file = await Windows.Storage.ApplicationData.Current.LocalFolder.GetFileAsync("myTest.pdf");
bool x = await Windows.System.Launcher.LaunchFileAsync(file);
return x;
}
}
}
cmdBarMailItem.IsEnabled = true;
}
catch (TaskCanceledException)
{
PopupRetrieve.IsOpen = false;
ProgressBar.IsVisible = false;
cmdBarMailItem.IsEnabled = true;
}
catch(Exception ex)
{
cmdBarMailItem.IsEnabled = true;
ProgressBar.IsVisible = false;
MessageBox.Show(AlertType.Connectivity);
}
return null;
}
async Task saveStringToLocalFile(string content)
{
try
{
// saves the string 'content' to a file 'filename' in the app's local storage folder
// byte[] fileBytes = System.Text.Encoding.UTF8.GetBytes(content.ToCharArray());
byte[] byteArray = Convert.FromBase64String(content);
// create a file with the given filename in the local folder; replace any existing file with the same name
StorageFile file = await Windows.Storage.ApplicationData.Current.LocalFolder.CreateFileAsync("myTest.pdf", CreationCollisionOption.ReplaceExisting);
// write the char array created from the content string into the file
using (var stream = await file.OpenStreamForWriteAsync())
{
stream.Write(byteArray, 0, byteArray.Length);
stream.Flush();
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
I got the exception on executing the line
string soapResponse = await response.Content.ReadAsStringAsync();
Anybody have an idea why the exception occurs ? What could be possible solution to fix it.
Any help would be appriciable. :)