Adjustment Internals
Prev | Chapter 11. Adjustments | Next

## Adjustment Internals

OK, you say, that's nice, but what if I want to create my own handlers to respond when the user adjusts a Range widget or a SpinButton. To access the value of a `Gtk::Adjustment`, you can use the `get_value()` and `set_value()` methods:

As mentioned earlier, `Gtk::Adjustment` can emit signals. This is, of course, how updates happen automagically when you share an Adjustment object between a Scrollbar and another adjustable widget; all adjustable widgets connect signal handlers to their adjustment's `value_changed` signal, as can your program.

So, for example, if you have a Scale widget, and you want to change the rotation of a picture whenever its value changes, you would create a signal handler like this:

    void cb_rotate_picture (Gtk::Widget *picture)
    {
      picture->set_rotation (adj->value);
    ...

and connect it to the scale widget's adjustment like this:

    adj.value_changed.connect(sigc::bind<Widget*>(sigc::mem_fun(*this, &cb_rotate_picture), picture));

What if a widget reconfigures the `upper` or `lower` fields of its Adjustment, such as when a user adds more text to a text widget? In this case, it emits the `changed` signal.

Range widgets typically connect a handler to this signal, which changes their appearance to reflect the change - for example, the size of the slider in a scrollbar will grow or shrink in inverse proportion to the difference between the `lower` and `upper` values of its adjustment.

You probably won't ever need to attach a handler to this signal, unless you're writing a new type of range widget.

    adjustment->changed();

Prev | Up | Next
Using Adjustments the Easy Way | Home | Chapter 12. Widgets Without X-Windows