Question

I open a FileStream to be written to Asynchronously.

m_oFile.BeginRead(arrInputReport, 0, m_nInputReportLength, new AsyncCallback(ReadCompleted), arrInputReport);

I dispose this using the following code:

if (bDisposing)
            {
                if (m_oFile != null)
                {
                    m_oFile.Dispose();
                    m_oFile = null;
                }

Unfortunately, after calling the dispose method, ReadComplete method still receives results:

protected void ReadCompleted(IAsyncResult iResult)
    {
        byte[] arrBuff = (byte[])iResult.AsyncState;    // retrieve the read buffer
        try
        {
                 m_oFile.EndRead(iResult);  

It will get a nullReference error at the m_oFile.EndRead line. Checking for null gets rid of the exception but just traps the program in this method. How can I dispose of the ReadComplete method?

Answer 1

If you don’t have reliable access to the instance you used, then I would suggest using the AsyncState to store all the things you need. For example:

var state = Tuple.Create(m_oFile, arrInputReport);
m_oFile.BeginRead(...blah... , ReadCompleted, state);

with:

var state = (Tuple<FileInfo, byte[]>)iResult.AsyncState;
FileInfo file = state.Item1;
byte[] arrBuff = state.Item2;

Note a null-check isn’t enough, because if a new file has been used, you would be calling it on the wrong FileInfo instance – not a good thing.