MemoryStream - Cannot access a closed Stream
C#asp.net.NetStreamwriterMemorystreamC# Problem Overview
Hi why using (var sw = new StreamWriter(ms))
returns Cannot access a closed Stream
exception
. Memory Stream
is on top of this code.
using (var ms = new MemoryStream())
{
using (var sw = new StreamWriter(ms))
{
sw.WriteLine("data");
sw.WriteLine("data 2");
ms.Position = 0;
using (var sr = new StreamReader(ms))
{
Console.WriteLine(sr.ReadToEnd());
}
} //error here
}
What the best way to fix it ? Thanks
C# Solutions
Solution 1 - C#
This is because the StreamReader
closes the underlying stream automatically when being disposed of. The using
statement does this automatically.
However, the StreamWriter
you're using is still trying to work on the stream (also, the using
statement for the writer is now trying to dispose of the StreamWriter
, which is then trying to close the stream).
The best way to fix this is: don't use using
and don't dispose of the StreamReader
and StreamWriter
. See this question.
using (var ms = new MemoryStream())
{
var sw = new StreamWriter(ms);
var sr = new StreamReader(ms);
sw.WriteLine("data");
sw.WriteLine("data 2");
ms.Position = 0;
Console.WriteLine(sr.ReadToEnd());
}
If you feel bad about sw
and sr
being garbage-collected without being disposed of in your code (as recommended), you could do something like that:
StreamWriter sw = null;
StreamReader sr = null;
try
{
using (var ms = new MemoryStream())
{
sw = new StreamWriter(ms);
sr = new StreamReader(ms);
sw.WriteLine("data");
sw.WriteLine("data 2");
ms.Position = 0;
Console.WriteLine(sr.ReadToEnd());
}
}
finally
{
if (sw != null) sw.Dispose();
if (sr != null) sr.Dispose();
}
Solution 2 - C#
Since .net45 you can use the LeaveOpen
constructor argument of StreamWriter
and still use the using
statement. Example:
using (var ms = new MemoryStream())
{
using (var sw = new StreamWriter(ms, leaveOpen:true))
{
sw.WriteLine("data");
sw.WriteLine("data 2");
}
ms.Position = 0;
using (var sr = new StreamReader(ms))
{
Console.WriteLine(sr.ReadToEnd());
}
}
Solution 3 - C#
When the using()
for your StreamReader
is ending, it's disposing the object and closing the stream, which your StreamWriter
is still trying to use.
Solution 4 - C#
when it gets out from the using statement the Dispose
method will be called automatically closing the stream
try the below:
using (var ms = new MemoryStream())
{
var sw = new StreamWriter(ms);
sw.WriteLine("data");
sw.WriteLine("data 2");
ms.Position = 0;
using (var sr = new StreamReader(ms))
{
Console.WriteLine(sr.ReadToEnd());
}
}
Solution 5 - C#
The problem is this block:
using (var sr = new StreamReader(ms))
{
Console.WriteLine(sr.ReadToEnd());
}
When the StreamReader
is closed (after leaving the using), it closes it's underlying stream as well, so now the MemoryStream
is closed. When the StreamWriter
gets closed, it tries to flush everything to the MemoryStream
, but it is closed.
You should consider not putting the StreamReader
in a using block.
Solution 6 - C#
In my case (admittedly very arcane and not likely to be reproduced often), this was causing the problem (this code is related to PDF generation using iTextSharp):
PdfPTable tblDuckbilledPlatypi = new PdfPTable(3);
float[] DuckbilledPlatypiRowWidths = new float[] { 42f, 76f };
tblDuckbilledPlatypi.SetWidths(DuckbilledPlatypiRowWidths);
The declaration of a 3-celled/columned table, and then setting only two vals for the width was what caused the problem, apparently. Once I changed "PdfPTable(3)" to "PdfPTable(2)" the problem went the way of the convection oven.