Re: gtkmm tutorial question

[Reece Dunn <msclrhd googlemail com>]

On 6 January 2011 15:36, Charles Seedle <charles seedle rigaku com> wrote:
> In the gtkmm tutorial on single item containers (Scrolled window) there is
> an example of a table with multiple toggle buttons. Unfortunetly the example
> doesn’t show how you can identify if one of the toggle buttons have been
> clicked, just the close button. You can setup the callback for an array of
> buttons. My issue is how do you determine which toggle button it was that
> was clicked. It can be done in Gtk+ but it eludes me how to get access to
> that kind of info in Gtkmm.  Getting the signal connection and callback
> parmeters correct seems to be the trick.
>
> For each button:
>
> buttons[x]->signal_clicked().connect(sigc::mem_fun(*this,
> &ExampleWindow::on_button_clicked));
>
> void ExampleWindow::on_button_clicked ()
> {
> }
>
>
> This will connect the buttons but it doesn’t pass enough info to figure out
> which button got clicked. Any ideas would be appreciated.

The signal_clicked().connect method takes a function object (functor).
That is, a class/struct that implements operator(). For example, you
could use:

   struct Test
   {
      void operator()() { printf("pressed!\n"); }
   };

   buttons[x]->signal_clicked().connect(Test());

   Test()(); // prints: pressed!

The sigc::mem_fun function creates a functor that binds to a class
function (your on_button_clicked in the example) with the class
instance (*this).

There is also a sigc::bind helper that binds a value to a function
parameter. That is:

   sigc::bind(Test(), arg)

maps to

   Test::operator()(arg)

when called, and takes no arguments. e.g.

   struct Test
   {
      void operator()(int arg) { printf("pressed button %d!\n", arg); }
   };

   sigc::bind(Test(), 10)(); // prints: pressed button 10

So, in your example, you can have:

   buttons[x]->signal_clicked().connect(
      sigc::bind(sigc::mem_fun(*this, &ExampleWindow::on_button_clicked), x));

   void ExampleWindow::on_button_clicked (int i)
   {
      button_type *button = buttons[x];
      ...
   }

HTH,
- Reece