Drop-down Lists

Drop-down lists are used to select from a mutually exclusive set of options. They can be useful when there is insufficient space in a window to use a group of radio buttons or a single-selection list, with which they are functionally equivalent.

Figure 6.17. A drop-down list showing current selection (left) and the list of available choices when clicked on (right)

Two images, one of a drop-down list displaying its current
          setting, and the other showing its popup menu of available choices
          when clicked on

Recommendations:

You should normally use radio buttons or a list instead of drop-down lists, as those controls present all the available options at once without any further interaction. However, drop-down lists may be preferable in a window where:

Drop-down lists can also be useful on toolbars, to replace a group of several mutually-exclusive toggle buttons.