How Do You Find Interface Implementation Overrides Via Reflection?
I’m working on some custom
FxCop rules and
one that I want to do is to catch people who try to call Dispose() on
objects deriving from
System.ServiceModel.ClientBase<T>
because they didn’t implement IDisposable in a safe
manner.
So you have ClientBase<T> which looks, in a very abbreviated fashion,
like this:
public abstract class ClientBase<TChannel> : ICommunicationObject,
IDisposable where TChannel : class
{
// Other stuff... and then
void System.IDisposable.Dispose()
{
this.Close();
}
}
Later, I might have a class that derives from that. Maybe a special type of client, and I might implement my own safe IDisposable version:
public class CustomClient : ClientBase<IMyService>,
IDisposable where TChannel : class
{
// Other stuff... and then
void System.IDisposable.Dispose()
{
try
{
this.Close();
}
catch
{
this.Abort();
}
}
}
Try not to get hung up on the hokey implementation there, just stick
with me - you have a sort of “overridden” Dispose() call. The thing is,
if I put my CustomClient in a using statement, it’s the “overridden”
Dispose() that executes, not the one in ClientBase<T>.
I want my FxCop rule to catch people who put something deriving from
ClientBase<T> in a using block, but if you’ve got an override like in
the CustomClient class there, I want it to let it go.
How do you detect that?
I’ve been all over the System.Reflection namespace and I can’t find
anything. If you do
Type.GetInterfaces()
or
Type.GetInterface()
it shows that you implemented IDisposable either way because it gets all
of the interfaces you implement all the way through the inheritance
chain.
Type.GetInterfaceMap()
only returns the base implementation - the one from ClientBase<T> - in
all cases. It ignores the derived class’s “override.” The only thing I
can figure out that seems to work, but feels really bad, is this:
public static bool OverridesDispose(Type runtimeType)
{
// For brevity, we're assuming the incoming Type isn't null and
// implements IDisposable. I've omitted those checks here.
MethodInfo info = runtimeType.GetMethod(
"Dispose",
BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
null,
new Type[] { },
null);
if (info == null)
{
info = runtimeType.GetMethod(
"System.IDisposable.Dispose",
BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
null,
new Type[] { },
null);
}
if (info == null)
{
return false;
}
Type declaringType = info.DeclaringType;
if (
declaringType.IsGenericType &&
declaringType.GetGenericTypeDefinition() == typeof(ClientBase<>)
)
{
return false;
}
return true;
}
See what I’m doing? I basically query for an implicit interface
implementation, then if that’s not found, I get the explicit interface
implementation. If neither are found, I figure there’s no override. If
one is found, then I ask what the declaring type of the method is, and
if it’s the ClientBase<T> type, it’s not overridden, otherwise it is.
But the code smell! Ugh!
Am I missing some easier way to do it?