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Fabian Binz | 12 May 2012 17:12
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Re: virtual list control

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

 

 

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.

 

 

 

Regards,

Fabian

 

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Jeremy O'Donoghue | 14 May 2012 10:43
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Re: virtual list control

Hi Fabian,

On 12 May 2012 16:12, Fabian Binz <fabianbinz-LWAfsSFWpa4@public.gmane.org> 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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Exclusive live event will cover all the ways today's security and 
threat landscape has changed and how IT managers can respond. Discussions 
will include endpoint security, mobile security and the latest in malware 
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/
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