A PropertyAction is a way to get a Action with a state value
reflecting and controlling the value of a Object property.
The state of the action will correspond to the value of the property. Changing it will change the property (assuming the requested value
matches the requirements as specified in the ParamSpec).
Only the most common types are presently supported. Booleans are mapped to booleans, strings to strings, signed/unsigned integers to
int32/uint32 and floats and doubles to doubles.
If the property is an enum then the state will be string-typed and conversion will automatically be performed between the enum value and
"nick" string as per the EnumValue table.
Flags types are not currently supported.
Properties of object types, boxed types and pointer types are not supported and probably never will be.
Properties of Variant types are not currently supported.
If the property is boolean-valued then the action will have a NULL parameter type, and activating the action (with no parameter) will
toggle the value of the property.
In all other cases, the parameter type will correspond to the type of the property.
The general idea here is to reduce the number of locations where a particular piece of state is kept (and therefore has to be
synchronised between). PropertyAction does not have a separate state that is kept in sync with the property
value -- its state is the property value.
For example, it might be useful to create a Action corresponding to the
"visible-child-name" property of a GtkStack so that the current page can be switched from a menu. The active radio indication
in the menu is then directly determined from the active page of the GtkStack.
An anti-example would be binding the "active-id" property on a GtkComboBox. This is because the state of the combobox itself
is probably uninteresting and is actually being used to control something else.
Another anti-example would be to bind to the "visible-child-name" property of a GtkStack if this value is actually stored in
Settings. In that case, the real source of the value is
Settings. If you want a Action to control
a setting stored in Settings, see
create_action instead, and possibly combine its use with
bind.