Hi Fabian,
On 12 May 2012 16:12, Fabian Binz fabianb...@yahoo.de wrote:
Hi Jeremy,
I don't know if you continued working on this, but I forked wxHaskell on
GitHub and tried to implement it myself:
https://github.com/FabianBinz/wxHaskell
I have been doing some work, but I don't have a lot of time right now, so
it is going more slowly than I would like.
For testing purposes, I only implemented the OnGetItemText and
SetItemCount method and it seems to work.
To implement the virtual list control, I defined a new class
wxVirtualListCtrl in wxc:
https://github.com/FabianBinz/wxHaskell/blob/master/wxc/src/include/virtuallistctrl_impl.h
Since it needs to invoke a callback function, I created the typedef
OnGetItemTextCallback. To make wxdirect accept this new type, I extended
the parser (patomtype) in ParseC.hs. This solution is very ad-hoc and I
think because wxc is supposed to be a language agnostic C wrapper, we
should maybe add another macro to wcx_types.hs (something like TCallback),
which is then recognized by wxdirect.
So, while this all works pretty well, there is unfortunately a memory leak
in Graphics.UI.WXCore.VirtualListCtrl, because of my use of newCString. At
the moment I don't know how to fix it and would be glad if someone could
give me some advice.
You need to use a finalizer - this is what I am looking into. There is an
overview at
http://www.haskell.org/haskellwiki/GHC/Using_the_FFI#Calling_Haskell_from_C,
but it could be clearer! Basic idea is that you free the CString when the
GC has no more references to the closure in which it is used.
I am using the event handler code as a model, since this already allows
callbacks from C to Haskell, and handles reference counting. Just haven't
finished yet.
I will take a look at your fork and see if you are further along than me,
and take code accordingly.
Best regards
Jeremy
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