[Kde-bindings] Qyoto: contructing a QPalette from a QColor

[Arno Rehn]

Am Montag, 16. Oktober 2006 11:26 schrieb Richard Dale:
> On Sunday 15 October 2006 16:38, Arno Rehn wrote:
> > Am Samstag, 14. Oktober 2006 22:04 schrieb Arno Rehn:
> > > Hi,
> > >
> > > I've just tried to port the Qt tutourial t11 to C# and came across the
> > > following error when trying to construct a QPalette from a QColor:
> > >
> > > [error message]
> > >
> > > It confuses me, that the stacktrace goes up to libsmokeqt.so.
> > > The example in qtruby is functional. Is there a need for special
> > > marshalling code or so?
> >
> > I've just tried some more things and the same problem occurs when
> > constructing a QRegion from a QRect. One thing they all have in common is
> > that they can be part of a QVariant. I looked through the QtRuby code and
> > didn't see any declaration of these types that cause problems (QRegion
> > and QPalette, there are more if I'm right). They're only in "class
> > Variant < Qt::Base". What does this mean?
>
> The problem was that there was no code to resolve ambiguous methods that
> were overloaded, when there was more than one possible candidate in the
> Smoke lib. It should be fixed now - so I hope this QRegion constructor is
> part of the same problem. We need to add a cache of C# MethodInfo to Smoke
> lib method ids so that the lookup only needs to be done once, as it's
> probably a bit slow - ie a Hashtable with a key of the MethodInfo for the
> method with a value of the Smoke method id as an int.  That's what QtRuby
> and PerlQt do, and we should do the same for Qyoto..
>
>     static private Hashtable methodCache = new Hashtable();
>     ...
>     methodCache[callMessage.MethodBase] = (object) methodId;

I've just written some code for this, but it doesn't work as expected. Somehow 
the MethodBase returned by 'callMessage' differs from the one returned by a 
normal Type-instance. This is a part of my code (methodCache is a global 
Hashtable containing other Hashtables for each class which in turn contain 
the methodIds):

		private void SetupMethodTable(Type klass) {
			Hashtable hash = new Hashtable();
			Console.WriteLine(klass.ToString());
			
			foreach (MethodInfo mi in klass.GetMethods(BindingFlags.Instance |
									BindingFlags.Public |
									BindingFlags.Static |
									BindingFlags.NonPublic)) {

				[Code for retrieving the mungedName]
				
				int methodId = FindMethod(mungedName, mi);
				hash.Add((MethodBase) mi, methodId);
			}
			methodCache.Add(klass, hash);
		}

Now if we want to retrieve our methodId from the Hashtable like this:

Hashtable methodIds = (Hashtable) methodCache[_instance.GetType()];

int methodId = (int) methodIds[(MethodInfo) callMessage.MethodBase];

we will get

Unhandled Exception: System.NullReferenceException: Object reference not set 
to an instance of an object

but only for some classes, not for all.
One way to work around it would be to create a method signature for each 
method on-the-fly and set this one as a key in the Hashtable, but this would 
cause several other difficulties and espacially a major slowdown (I've 
already tried it).
Maybe I do something wrong, but I would leave it as it is at the moment.

-- 
Arno Rehn
arno at arnorehn.de