Some ListBox widget ideas and proposals:

See screenshot: https://lh6.googleusercontent.com/TAVZGw63BSVVT6Nh8hXbiHerZ3L0krBzboONI07PpFByROeqKPiFgrlaPnTMtIUZ94D8xRog=w1920-h960

1. Add two search fields, so it is possible to search within the left and right panes individually.
2. Add headers above the search fields. They can be configured via templates. Also add options for selecting/deselecting all items in the corresponding pane. Checkbox’s middle state should also be considered.
3. Add option (API) for enabling/disabling ListBox widget as a whole widget (similar to DropDownList, ComboBox, etc.), not only item by item.
4. Add support for data virtualization (similar to DropDownList, ComboBox and AutoComplete).
5. Add API (public methods or fields) for retrieving the current status of the items in the ListBox. For example:
- a method/property which returns the count of currently selected items
- a method/property which returns the count of currently showed items (if searching, not all items will be visible)
- a method/property which returns the count of total items
This information can be shown in the headers via template, for example.