Hello Michael Dunbar,
I already answered your question in the support ticket, but I will give the information here as well, so that it is available to all:
In case I understand you correctly, you would like to set
Width=Unit.Empty and the RadSlider control to calculate its width based
on the number of its items. Even though this sounds logical in some
cases, in general, this raises some question - e.g. what should be the
width of each item (e.g. the width of its text; the width of the
longest item text; predefined width; etc.). In my opinion this question
has no general answer. For example, in case the control had a property
ItemWidth, we could calculate the control width based on this value.
However, you will still need to set this ItemWidth property.
As you can set the Width of the RadSlider control dynamically, I would
recommend that you set the value of that property based on the number
of items you have.
the Telerik team