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();