Drop-down Combination Boxes
Drop-down combination boxes combine a text entry field and a dropdown list of pre-defined values. Selecting one of the pre-defined values sets the entry field to that value.
Figure 6-18 A drop-down combination box before and after its dropdown list is displayed
Guidelines
- Only use a drop-down combination box instead of a list, drop-down list or radio button group when it is important that the user be able to enter a new value that is not already amongst the list of pre-defined choices.
- Do not initiate an action when the user selects an item from the list in a drop-down combination box. If used in an instant-apply property or preference window, update the setting represented by the drop-down combination box immediately if possible. If this isn't possible due to the contents of the entry field being invalid while the user is still typing into it, update the related setting when the drop-down combination box loses focus instead.
- If the user types a value into the drop-down combination box that is not already in the drop-down list, add it to the list when the drop-down combination box loses focus so they can select it next time.
- Interpret user input into a drop-down combination box in a case-insensitive way. For example, if the user types blue, Blue and BLUE into the same drop-down combination box on different occasions, only store one of these in the combo's dropdown list, unless your application makes a distinction between the different forms (which is usually a bad idea).
- Label the drop-down combination box with a text label above it or to its left, using sentence capitalization. Provide an access key in the label that allows the user to give focus directly to the drop-down combination box.
- Use sentence capitalization for the dropdown list items, for example Switched movement.