I do understand what are trying to achieve. What I do not understand, is how you expect the RadSlider to look when you have Value="null". In case you would like:
- the dragHandle to be hidden
- the selection to be hidden
- when the user clicks on an item, the dragHandle and the selection to appear
, I cannot agree with you that such slider would visually "tell" the user that he/she has to select a value by dragging something that is, at this point, invisible.
You can however, use the client-side API
of the RadSlider to achieve this. In case you decide to implement this approach and have problems, please send me your code and I will do my best to help you.
The contradiction in this case comes from the fact that a slider control should at any point in time, "point" to the currently selected item. And in the definition of the RadSlider that you have provided, there is no "null" item defined. However, in case you define such an item, it becomes a valid value.
the Telerik team