Question

the following code is from MSDN: Idisposable pattern

protected virtual void Dispose(bool disposing)
    {
        // If you need thread safety, use a lock around these 
        // operations, as well as in your methods that use the resource.
        if (!_disposed)
        {
            if (disposing) {
                if (_resource != null)
                    _resource.Dispose();
                    Console.WriteLine("Object disposed.");
            }

            // Indicate that the instance has been disposed.
            _resource = null;
            _disposed = true;   
        }
    }

why the following statement:

 _resource = null;  
_disposed = true; 

are not enclosed by if (disposing) statement block?

for me i would probably write like this:

if (disposing) {
       if (_resource != null) {
            _resource.Dispose();
            _resource = null;
            _disposed = true;
           }
         Console.WriteLine("Object disposed.");
   }

anything wrong with my version?

Answer 1

The pattern outlined by the MSDN is the only correct way to implement IDisposable because it takes finalization into account. You need to look closely at the IDisposable implementation:

public void Dispose() 
{
    Dispose(true);

    // Use SupressFinalize in case a subclass
    // of this type implements a finalizer.
    GC.SuppressFinalize(this);      
}

This calls your dispose method, indicating it’s a real dispose and supresses further finalization.

It’s not safe to call out to any other object during finalization, so that’s why you want to set:

 _resource = null;  
_disposed = true; 

to prevent any further mishappenings.

Here’s a good info on finalization and IDisposable on MSDN.