How to fix memorystream object getting disposed exception?

Question

1.00/5 (2 votes)

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Hello!

I have a memoryStream object that I am passing from one method to another, each method is in a seperate class.
When I build this memorystream in the 1st method, it is working fine but when I pass it to the next method in another class, I get a "System.ObjectDisposedException: Cannot access a closed Stream"
So I guess this stream is not getting carried to the other method to be processed?

Can someone please assist in this problem so I can process the stream and keep it intact and not to be disposed in another class?

Thank you!

What I have tried:

I tried searching for solutions but I didn't find anything clear enough to be guided with.
Below, the stream in Class2 is where I am getting the exception.

Here is part of the code:

Class1.cs:

C#

 public MemoryStream? Export()
{
-
-
-
 using var stream = new MemoryStream();
-
-(for and foreach loops){
-
workBook.SaveAs(stream); //using ClosedXML library
-
-
}
return stream;
}

Class2.cs:

C#

public async Task<MemoryStream?> SaveCovers()
{
-
-//some unrelated code
-
try
{
var stream = _coverExcelService.Export(countryId, involvedProperties, calculatedInfo.Select(s => s.year).Distinct().ToArray());
return stream;
}
catch (Exception e1)
{
var msg = e1.Message;
}
}
return null;
}

Posted 22-Sep-23 7:05am

xTMx9

Updated 24-Sep-23 23:18pm

v2

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3 solutions

Solution 3

You need to go lookup what "using" does in C#.

Your code:

C#

 public MemoryStream? Export()
{
    using var stream = new MemoryStream();

    ... blah ...

    return stream;
}

That "using" statement is telling the code to dispose the stream object when the method ends and returns to the caller. Get rid of the "using" and the object will survive being returned. Oh, and you don't need a ? on the end of the return type since your code has no choice but to actually return a MemoryStream object.

C#

 public MemoryStream Export()
{
    MemoryStream stream = new MemoryStream();

    ... blah ...

    return stream;
}

using statement - ensure the correct use of disposable objects - C# | Microsoft Learn[^]

Quote:
When declared in a using declaration, a local variable is disposed at the end of the scope in which it's declared. In the preceding example, disposal happens at the end of a method.

That scope, in your example, is the end of the Export method.

Posted 25-Sep-23 3:41am

Dave Kreskowiak

Updated 25-Sep-23 3:45am

v2

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OriginalGriff · Accepted Answer · 2023-09-22T08:54:00

Solution 1

Without your code for both methods, we can't tell for sure - there are so many ways you could be doing things.

But ... we can guess based on the almost negligible amount of information you have given us. If you are creating a stream in one method which calls a second and passes the stream as a parameter, it's really unlikely that the Garbage collector reliably came in at the same point and Disposed it, particularly since the first method still has a reference to the stream for the life of the second.
So from that, it has to be your code: it contains a using block around the stream creation, or a Dispose call in a finally block.

Look at your code: the stream isn't being Disposed behind the scenes, so you have somewhere manually killed it!

Posted 22-Sep-23 8:54am

OriginalGriff

Comments

Dave Kreskowiak 22-Sep-23 15:56pm

Or the MemoryStream went out of scope between calls to the other methods.

OriginalGriff 22-Sep-23 17:17pm

Still wouldn't be reliably Disposed - the GC ain't that quick to chime in! :laugh:

xTMx9 25-Sep-23 5:20am

Hello! I have updated the question and added a code part.
I have a "using var stream = new MemoryStream();" part in the class.
So I assume at the end of this method, the object is getting disposed? Is there a good way to pass the stream to the 2nd class without it being disposed?

OriginalGriff 25-Sep-23 5:50am

That's what Using does: it says to the system "when this variable goes out of scope, Dispose it automatically" - it doesn't matter how it goes out of scope - end of a block or method, or an exception, or a Finally block - as soon as it's no longer needed, it is thrown away and can't be accessed.

If you want to pass it back to the calling method, remove the "using" and Dispose it manually yourself when you are finished with it.

Graeme_Grant 25-Sep-23 5:51am

And that is the problem.

using var stream = new MemoryStream();

This is the same as:

using var stream = new MemoryStream()
{
 // do work here
}

The return statement is taking the stream out of scope and the stream is being automatically closed.

For it to work, you need to pass the stream in, not out...

public void Export(MemoryStream stream)
{
    // do work here
}

OriginalGriff 25-Sep-23 6:30am

I wish these people would learn the language before they copy'n'paste'n'hope ... :sigh:

Graeme_Grant 25-Sep-23 6:36am

I contemplated posting both usages but chose to keep it simple ... Hopefully, the above explains his "new" issue. The error message is the clue being ignored.

OriginalGriff 25-Sep-23 6:46am

"Clues? I don't need no stinking clues! You have to think to work them out and that's your job!" :sigh:

Graeme_Grant 25-Sep-23 7:05am

lol...

xTMx9 26-Sep-23 5:34am

Thanks for the clarification, I got it.

Graeme_Grant 26-Sep-23 6:30am

Glad to hear! :)

Graeme_Grant · Accepted Answer · 2023-09-23T02:05:00

To expand on what @OriginalGriff has said, here is an example of what he was talking about:

C#

static void Main(string[] args)
{
    // Create a MemoryStream to write text to
    using (MemoryStream memoryStream = new MemoryStream())
    {
        // Write text to the MemoryStream
        string textToWrite = "Hello, this is some text written to a MemoryStream!";
        byte[] bytesToWrite = Encoding.UTF8.GetBytes(textToWrite);
        memoryStream.Write(bytesToWrite, 0, bytesToWrite.Length);

        // Reset the position to the beginning of the MemoryStream
        memoryStream.Seek(0, SeekOrigin.Begin);

        // Read the text back from the MemoryStream
        ReadStream(memoryStream);
    }
}

private static void ReadStream(MemoryStream memoryStream)
{
    using (StreamReader reader = new StreamReader(memoryStream, Encoding.UTF8))
    {
        string textRead = reader.ReadToEnd();
        Console.WriteLine("Text read from MemoryStream: " + textRead);
    }
}

Notice that I am using a using statement that sets the scope of the usage within the braces. I do it with the MemoryStream and StreamReader classes. Both classes implement the IDisposable interface. So when the code goes out of scope, the MemoryStream and StreamReader classes will automatically call their Close methods from the implemented IDisposable.Dispose method and release any resources in use.

If you want to implement this manually, you would do the following:

C#

static void Main(string[] args)
{
    // Create a MemoryStream to write text to
    MemoryStream memoryStream = new MemoryStream();
    
    // Write text to the MemoryStream
    string textToWrite = "Hello, this is some text written to a MemoryStream!";
    byte[] bytesToWrite = Encoding.UTF8.GetBytes(textToWrite);
    memoryStream.Write(bytesToWrite, 0, bytesToWrite.Length);

    // Reset the position to the beginning of the MemoryStream
    memoryStream.Seek(0, SeekOrigin.Begin);

    // Read the text back from the MemoryStream
    ReadStream(memoryStream);
    
    memoryStream.Close();
}

private static void ReadStream(MemoryStream memoryStream)
{
    StreamReader reader = new StreamReader(memoryStream, Encoding.UTF8);

    string textRead = reader.ReadToEnd();
    Console.WriteLine("Text read from MemoryStream: " + textRead);

    reader.Close();
}

Note: the above code is dangerous as it is possible for the instances not to be close. Hence why the using statement is used.