Re: Correct signal handler to overload in a treeview to STOP the selection from changing

[Bob Caryl <bob fis-cal com>]

Huston, Bob wrote:

> I have a treeview derived class, in which when a branch in the tree is 
> displayed I display a
> notebook derived class showing many GUI controls for information 
> gathering. When
> the user selects a different branch in the tree, I save off the 
> currently displayed notebook information
> and display a new notebook for the new branch that is selected.
>  
> I accomplish this by overloading the on_cursor_changed signal handler 
> in the tree view class.
>  
> The issue I am having is that when I am switching notebooks being 
> displayed I validate any and all
> information on the current notebook, if the information is valid, I 
> want to warn the user via and keep the
> tree from switching views. 
>  
> I am not switching the notebooks when this occurs, however the tree is 
> still switching which branch is selected.
>  
> My code basically is this:
>  
> void CMyTreeView::on_cursor_changed()
> {
>     // save/validate the current notebook:
>     if ( !SaveCurrentNotebook())
>         return;
>  
>     // put up the new notebook
>     .....
>     return Gtk::TreeView::on_cursor_changed();
> }
>  
> I need to know how to either return from this handler so that the 
> selection doesn't change, or a different handler
> to overload to do my processing prior to the selection change occurs.  
> I thought that by not allowing the
> parent tree view class's version of on_cursor_changed to be called 
> that this would happen.
>  
> --Bob
>  
>
> ------------------------------------------------------------------------
>
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>  

Hey Bob,

I could not find a signal directly relating to the Gtk::TreeView to 
which you could connect in order to prevent the TreeView from changing 
rows in response to a mouse click (and remember, a row can also be 
changed with the arrow keys on the keyboard).  However, you might 
consider connecting to "Gtk::Main::signal_key_snooper" and looking for a 
"GDK_BUTTON_PRESS" event (see GdkEventButton 
http://www.gtk.org/api/2.6/gdk/gdk-Event-Structures.html#GdkEventButton 
<http://www.gtk.org/api/2.6/gdk/gdk-Event-Structures.html#GdkEventButton>).  
You can compare the GdkWindow pointer to the GdkWindow corresponding to 
your Gtk::TreeView in your connected callback slot to determine whether 
or not to allow the cursor to change depending on the validation of your 
controls in your notebook page.

Connection code looks like this:

Gtk::Main::signal_key_snooper().connect(sigc::mem_fun(*this,&<your class 
name here>::<your callback slot name here>));

I don't know if this will actually work, but I do know that you can 
choose to go ahead a propagate the event or not in your callback.  If 
you do propagate it, you must be sure to prevent catching that event a 
second (and third and fourth and so forth) time.

Hope this might help.

Bob Caryl

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