A dual Listbox allows users to compare and move available and selected options between two lists.
A dual Listbox consists of two lists used to move options between them. Users are allowed to multi-select different items from a list and sometimes, options in use can be re-order. The scroll must be available in long lists.
In usex Listbox. This box displays selected or preselected options in use. It is always shown on the left side of the component. This list can allow manual ordering if necessary.
Available Listbox. This box displays a fixed set of options available to the user and it does not show those options that are already in use. It is always shown on the right side of the component.
Transfer buttons. These buttons are always visible showing their different states to help users filter the actions available.
Order buttons. These buttons only appear within an area to indicate that ordering is available on a specific list. Order buttons don’t need to be shown if the dual Listbox doesn't require ordering.
To help users making sense of the use of a dual Listbox, we recommend not only to label the boxes but to provide some context to describe the main goal of the task that can be carried.
A selection is used to highlight an option when users select it. Single selection and multiple selections are available using touch or keyboard actions. When one or more selected options are out of focus, a secondary selection is used.
In a Dual Listbox, left and right carets are used to symbolize moving actions from one list to the other. After an item(s) has been selected, these buttons move the items. Transfering buttons are always displayed but different states are used to guide the user to select the desired action.
Transfer buttons are disabled when there are no items selected.
If one of the boxes is on focus but no items are selected, transfer buttons must remain disabled.
When one or more items are selected in the In use Listbox, the right caret turns into a default state but the left caret must continue disabled. After clicking an item in the available list, the left caret will be shown in the default state and the right caret will remain disabled.
After items are moved to the In Use Listbox from the Available list, they must remain highlighted with a secondary selection in the new box as a visual confirmation. However, the position in which items are placed depends on whether the In Use Listbox allows manual ordering or not. If manual ordering is allowed, items will be added to the bottom of the list. On the contrary, if manual ordering is not allowed, items will be placed automatically in alphabetical order.
After items are moved to the Available Listbox, they don’t need to remain highlighted and will be placed automatically in alphabetical order.
When manual ordering is available in the In Use Listbox, top and bottom carets are used to symbolize moving elements up and down. These buttons appear within the area of the list and are only displayed if there is more than one item on the list.
If there is one or no elements on the list when manual ordering is available in the component, ordering buttons are not shown.
If there is more than one element in the In Use list but there are no selected items, ordering buttons must be visible but they must remain disabled.
After selecting an item from the list, ordering buttons must display the default states of the available actions.
When two or more separated items are selected from the list and the user wants to bring both items to the top (or bottom) of the list, once the first item has reached the top, it should be kept there while the rest of item(s) keep moving up until they are completely stacked.
To improve the usability of this component, when an item has reached the top of the list, users shouldn’t be able to keep moving this item upwards as this will cause an infinite loop bringing the top item to the bottom of the list and getting the user confused. Moving an item(s) to the bottom of the list should have the same restriction.