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 automatically 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();

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