I'm new to C#, so apologies if this is an obvious question.
In the MSDN Dispose example, the Dispose method they define is non-virtual. Why is that? It seems odd to me - I'd expect that a child class of an IDisposable that had its own non-managed resources would just override Dispose and call base.Dispose() at the bottom of their own method.
Thanks!
Typical usage is that Dispose() is overloaded, with a public, non-virtual Dispose() method, and a virtual, protected Dispose(bool). The public Dispose() method calls Dispose(true), and subclasses can use this protected virtual method to free up their own resorces, and call base.Dispose(true) for parent classes.
If the class owning the public Dispose() method also implements a finalizer, then the finalizer calls Dispose(false), indicating that the protected Dispose(bool) method was called during garbage collection.
If there is a finalizer, then the public Dispose() method is also responsible for calling GC.SuppressFinalize() to make sure that the finalizer is no longer active, and will never be called. This allows the garbage collector to treat the class normally. Classes with active finalizers generally get collected only as a last resort, after gen0, gen1, and gen2 cleanup.
This is certainly not an obvious one. This pattern was especially choosen because it works well in the following scenario's:
While a virtual Dispose() method will work in the scenario where classes don't need finalization, it doesn't work well in the scenario were you do need finalization, because those types often need two types of clean-up. Namely: managed cleanup and unmanaged cleanup. For this reason the Dispose(bool) method was introduced in the pattern. It prevents duplication of cleanup code (this point is missing from the other answers), because the Dispose() method will normally cleanup both managed and unmanaged resources, while the finalizer can only cleanup unmanaged resources.