Re: Using Trees

[Murray Cumming <murrayc murrayc com>]

On Sat, 2010-06-26 at 14:28 -0400, Joe LaBarbera wrote:
> Hi,
> 
> I was trying to append allow a user to click a button that would allow 
> an additional column to be appended to my tree.
> 
> This is what I have:
> 
> void treetstruct::add_column()
> {
>      Gtk::TreeModelColumn<unsigned> newcol = columns.addcol();
> 
>      treeview.append_column_editable("New", columns.cols.back());
> }
> 
>          Gtk::TreeModelColumn<unsigned> addcol()
>          {
>                 Gtk::TreeModelColumn<unsigned> newcol;
>                 cols.push_back(newcol);
>                 add(cols.back());
> 
>                 return cols.back();
>          }

But your model knows nothing about these new columns.
TreeModelColumnRecord (your cols) is just a way to remember details
about model columns. You probably supplied it to a ListStore or
TreeStore create() method:
http://library.gnome.org/devel/gtkmm/stable/classGtk_1_1ListStore.html#aaa6c530560f66872482a0650739276c5

But your cols object is not shared. The model won't change in response
if you later change the TreeModelColumnRecord.

Basically, there is no TreeModel::add_column() method. You must recreate
your entire model when you want to add a column. I often wish that it
was more flexible, but it does make some sense: Adding a column means
that you've changed your data structure.

> The column will appear; however, when I attempt to change values, they 
> are automatically erased, and there are many errors that appear in the 
> command line.  If anyone could help, even by providing additional 
> information on trees in general, I would really appreciate it.


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