7.2.3 Collection gadgets

7.2.3.1 Useful properties of collection gadgets

All collection gadgets share certain essential properties. These can either be specified when an instance of a gadget is created, using an init-keyword, or set interactively via a slot value.

gadget-items: This slot contains a Dylan collection representing the contents of a collection gadget.
gadget-label-key
: The label key is a function that is used to compute the label of each item in a collection gadget, and therefore defines the "printed representation" of each item. If gadget-label-key is not explicitly defined for a collection gadget, its items are labeled numerically.
gadget-value-key
: Similar to the label key, the value key is used to compute a value for each item in a collection gadget. The gadget value of a collection gadget is the value of any selected items in the collection gadget.
gadget-selection-mode
: The selection mode of a collection gadget determines how many items in the gadget can be selected at any time. This takes one of three symbolic values: #"single" (only one item can be selected at any time), #"multiple" (any number of items can be selected at once), #"none" (no items can be selected at all).
: Note that you can use gadget-selection-mode to read the selection mode of a gadget, but you cannot reset the selection mode of a gadget once it has been created. Instead, use the selection-mode: init-keyword to specify the selection mode when the gadget is created.
: Generally, different subclasses of collection gadget specify this property automatically. For example, a radio box is single selection, and a check box is multiple selection.

To specify any of these slot values as an init-keyword, remove the gadget- prefix. Thus, the gadget-value-key slot becomes the value-key: init-keyword.