Question

I have an object that uses some underlying native resources, and has a pointer to the next instance, which I iterate through similar to:

MyObject begin = null;

try
{
    begin = GetFirst();

    while (begin != null)
    {
        MyObject next = begin.Next();
        // do something with begin
        begin.Dispose();
        begin = next;
    }
}
finally
{    
    if (begin != null)
    {
        begin.Dispose();
    }
}

I get the code analysis problem:

CA2202: Microsoft.Usage: Object ‘begin’ can be disposed more than once in method ‘x()’. To avoid generating a System.ObjectDisposedException you should not call Dispose more than one time on an object.

Any idea how I can get rid of this error without suppressing it?

Answer 1

It certainly seems to me that your last block of code is unnecessary. If begin != null, then your while loop should have continued, no?

UPDATE: It looks like you’re trying to ensure the last obtained value for begin is disposed in case an exception is thrown. Try this:

MyObject begin = GetFirst();

while (begin != null)
{
    MyObject next;
    using (begin)
    {
        next = begin.Next();
        // do something with begin
    }

    begin = next;
}

Note that in the above suggestion, it could actually still happen that you end up with an undisposed object: the last value assigned to next, before the end of the using block. This scenario wasn’t covered in your original question, so I haven’t addressed it in the above suggestion. It’s something to consider, though, if that’s a potential problem.