Re: [gtkmm] writing a custom cellrenderer

[Daniel Sundberg <dss home se>]

Roel Vanhout wrote:
> Hello all,

Hi,

have you looked at the example located in examples/customcellrenderer in 
the gtkmm source distribution. I have successfully created a custom cell 
renderer in my program GSpeakers based on this example. Please have a 
look at:

http://cvs.sourceforge.net/viewcvs.py/gspeakers/gspeakers2/src/cellrendererpopup.h?view=markup
http://cvs.sourceforge.net/viewcvs.py/gspeakers/gspeakers2/src/cellrendererpopup.cc?view=markup

http://cvs.sourceforge.net/viewcvs.py/gspeakers/gspeakers2/src/cellitemcrossover.h?view=markup
http://cvs.sourceforge.net/viewcvs.py/gspeakers/gspeakers2/src/cellitemcrossover.cc?view=markup

Regards

Daniel Sundberg

---
http://sumpan.com

> I spend the bigger part of yesterday evening trying to write a custom 
> cellrenderer for Gtk::TreeView but I didn't get it to work. I'm porting 
> an application from plain C Gtk to C++ with gtkmm. In the original 
> application I used the code from 
> http://scentric.net/tutorial/sec-custom-cell-renderers.html, which was 
> luckily exactly what I needed (in C). I thought that for a C++ version 
> all I'd have to is derive my own class from Gtk::CellRenderer, override 
> a few methods (that would have been declare pure virtual so that the 
> compiler would point me to them) and that would be it. Turns out I was 
> wrong.
> I started by looking at 
> http://www.gtkmm.org/docs/gtkmm-2.4/docs/reference/html/classGtk_1_1CellRend
> erer.html. 
> I didn't see anything there that indicated what functions I had to 
> override to make my own so I just write a small class, overriding 
> get_size(), _property_renderable() and render() and copied the code from 
> my original C renderer to the corresponding functions. I had to massage 
> it a bit to get it into C++ format and then it compiled. I used the 
> add_column() method that takes a custom renderer and when all of that 
> compiled I thought it'd work, but all I saw was a blank cell. So I 
> looked at the implementation of the CellRendererText and -Pixbut in the 
> gtkmm source and to my horror I found all the structs from the C version 
> in there - the init thing and a sort of virtual vtable and all the 
> things I hoped I would never have to bother with again when I switched 
> to gtkmm. I'm still hoping that this is only because they wrap the C 
> version and that it is possible to write one in pure C++.
> Ok so sorry if this sounds frustrated (it's because I am), but here are 
> a few questions that I have:
>
> - What functions do I have to override and what do I have to implement 
> to get a custom cellrenderer, a complete new one and not one that just 
> wraps a C version? I think I'm missing two things: first, registering a 
> custom property ('progress' in my case), and secondly registring the 
> cellrenderer itself somewhere.
> - All properties (like property_xalign()) have comments like "You rarely 
> need to use properties because there are get_ and set_ methods for 
> almost all of them.". But are there really? Where are they declared? How 
> should I use those properties?
> - What are the protected methods in CellRenderer (like get_size_vfunc() 
> ) used for? Should I override them?
> - Why are there two versions of get_size? Is there an easy way to 
> implement the one in terms of the other or should I write full 
> implementations for both?
>
> I've attached the code that I have so far. Some of it is commented out, 
> that's what I was trying after I got everything to compile but when it 
> didn't work. It's mostly copied from CellRendererText, but that one 
> wraps the C version so it's not quite the same as what I try to do.
> Thanks in advance.
>
>
> cheers,
>
> roel
>
>
>
>
>
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