public ActionResult CustomChart(int reportID)
{
Chart chart = new Chart();
// Save the chart to a MemoryStream
var imgStream = new MemoryStream();
chart.SaveImage(imgStream);
imgStream.Seek(0, SeekOrigin.Begin);
// Return the contents of the Stream to the client
return File(imgStream, "image/png");
}
I am accustomed to using the 'using' statement in conjuction with MemoryStreams. Is this a scenario where the 'using' statement is not necessary? Or is it valid to call return inside of a 'using' statement?
EDIT:
For my purposes I have found that the introduction of a 'using' statement does NOT work (throws an ObjectDisposedException). Here's what I'm doing with it client-side:
$('#ReportTest').bind('load', function () {
$('#LoadingPanel').hide();
$(this).unbind('load');
}).bind('error', function () {
$('#LoadingPanel').hide();
$(this).unbind('error');
}).attr('src', '../../Chart/CustomChart?ReportID=' + settings.id);
Does a MemoryStream get disposed of automatically when returning it as an ActionResult?
Yes, MVC (at least version 3) will clean it up for you. You can take a look at the source of the WriteFile
method in FileStreamResult
:
protected override void WriteFile(HttpResponseBase response) {
// grab chunks of data and write to the output stream
Stream outputStream = response.OutputStream;
using (FileStream) {
byte[] buffer = new byte[_bufferSize];
while (true) {
int bytesRead = FileStream.Read(buffer, 0, _bufferSize);
if (bytesRead == 0) {
// no more data
break;
}
outputStream.Write(buffer, 0, bytesRead);
}
}
}
The line using (FileStream) {
will place the Stream in a using block, thus Disposing of it when it has written the contents to the Http Response.
You can also verify this behavior by creating a dummy stream that does this:
public class DummyStream : MemoryStream
{
protected override void Dispose(bool disposing)
{
Trace.WriteLine("Do I get disposed?");
base.Dispose(disposing);
}
}
So MVC will dispose it.