Uploading large pictures to FTP freezes the app - xamarin.forms

Question

I am trying to upload some pictures to my FTP in a form. It´s working great on my Huawei P20, but it has been reported to me that on a phone with less RAM the app freezes when they are trying to upload larger pictures.
After the picture selection (max of 4) I resize the images and compress them to reduce the size, but with no luck
Code:
public static byte[] RotateImage(string path)
{
byte[] imageBytes;
var originalImage = BitmapFactory.DecodeFile(path);
var rotation = GetRotation(path);
//Width 3000 Height 4000
var width = (originalImage.Width * 0.25);
var height = (originalImage.Height * 0.25);
if(originalImage.Height>2400)
{
width = (originalImage.Width * 0.20);
height = (originalImage.Height * 0.20);
}
if (originalImage.Height < 600)
{
width = (originalImage.Width * 0.80);
height = (originalImage.Height * 0.80);
}
var scaledImage = Bitmap.CreateScaledBitmap(originalImage, (int)width, (int)height, true);
Bitmap rotatedImage = scaledImage;
if (rotation != 0)
{
var matrix = new Matrix();
matrix.PostRotate(rotation);
rotatedImage = Bitmap.CreateBitmap(scaledImage, 0, 0, scaledImage.Width, scaledImage.Height, matrix, true);
scaledImage.Recycle();
scaledImage.Dispose();
}
using (var ms = new MemoryStream())
{
if (rotatedImage.Width > 1000 || rotatedImage.Height > 1000)
{
rotatedImage.Compress(Bitmap.CompressFormat.Jpeg, 30, ms);
}
if (rotatedImage.Width < 500 || rotatedImage.Height < 500)
{
rotatedImage.Compress(Bitmap.CompressFormat.Jpeg, 60, ms);
}
if (rotatedImage.Width <= 1000 && rotatedImage.Width >= 500)
{
rotatedImage.Compress(Bitmap.CompressFormat.Jpeg, 45, ms);
}
imageBytes = ms.ToArray();
}
originalImage.Recycle();
rotatedImage.Recycle();
originalImage.Dispose();
rotatedImage.Dispose();
GC.Collect();
return imageBytes;
}
Then I send them to the MessagingCenter and retrieve them in PCL.
The application freezes when I try to upload it to FTP
Code in PCL:
for (int i = 0; i < _images.Count; i++)
{
DependencyService.Get<IFtpWebRequest>().upload("FTP", _images[i], "SITE", "PASSWORD", "DIRECTORY");
}
and the platform specific code I am calling is:
public string upload(string FtpUrl, string fileName, string userName, string password, string UploadDirectory = "")
{
try
{
WebRequest request = WebRequest.Create(FtpUrl+UploadDirectory);
request.Method = WebRequestMethods.Ftp.MakeDirectory;
request.Credentials = new NetworkCredential(userName, password);
using (var resp = (FtpWebResponse)request.GetResponse())
{
}
}
catch(Exception e) { }
try
{
string PureFileName = new FileInfo(fileName).Name;
String uploadUrl = String.Format("{0}{1}/{2}", FtpUrl, UploadDirectory, PureFileName);
FtpWebRequest req = (FtpWebRequest)FtpWebRequest.Create(uploadUrl);
req.Proxy = null;
req.Method = WebRequestMethods.Ftp.UploadFile;
req.Credentials = new NetworkCredential(userName, password);
req.UseBinary = true;
req.UsePassive = true;
byte[] data = File.ReadAllBytes(fileName);
req.ContentLength = data.Length;
Stream stream = req.GetRequestStream();
stream.Write(data, 0, data.Length);
stream.Close();
FtpWebResponse res = (FtpWebResponse)req.GetResponse();
return res.StatusDescription;
}
catch (Exception err)
{
return err.ToString();
}
}
The expected result should be the app not freezing on any phone.
What could I do to prevent it?
Further increasing compression isnt best solution either as some phones upload it no problem and therefore I could achieve higher quality.
EDIT: When uploading a large picture to FTP and I check the pic on FTP its like 1/10 of the picture is uploaded, rest is blank
EDIT2: Moving the function to a different thread does not freeze the application anymore but still only part of the iamge is uploaded on devices with less memory, how do I somehow force the whole image to be uploaded?

Answer 1

When uploading a large picture to FTP and I check the pic on FTP its like 1/10 of the picture is uploaded, rest is blank
If the uploaded image is very large, then this will be a time-consuming operation. If it is placed in the main UI thread, it will consume a lot of memory and time. When the memory of the mobile phone is large, it may be able to do the task, but when When the phone is not big, then the problem will arise.
You need to move upload method to a backgroud thread, then it will not affect UI thread.
If in Android , Have a try with Task :
public async Task<string> upload(string FtpUrl, string fileName, string userName, string password, string UploadDirectory = "")
{
await Task.Run(() =>
{
try
{
WebRequest request = WebRequest.Create(FtpUrl+UploadDirectory);
request.Method = WebRequestMethods.Ftp.MakeDirectory;
request.Credentials = new NetworkCredential(userName, password);
using (var resp = (FtpWebResponse)request.GetResponse())
{
}
}
catch(Exception e) { }
...
});
}