I was recently playing with the UocDropDownList control in the RCDCs and came across a couple things that are in the documentation but not really defined that clearly. I went around digging and found a couple simple examples which allowed me to distill the following:
Setting a default value for a drop down list
By default, if you use the “custom” settings for the list and include the options, the first option in the list is the default. This is really handy when setting up an object where the majority of the items will always fit the same series of settings and the user is properly informed of how the object is created by default and that they should look at and change the settings.
Forcing the user to select a value
This is where things got interesting with the drop down controls. The fix for it was really quite simple although with some of the iterations that were played with, the results were unexpected.
If you have the control set to “required” and the list of options as set out in the “setting a default value for a drop down list” noted above. Where there is simply a list of the options you want, the first option in that list will be selected if the drop down isn’t changed.
An interesting item that I did notice however, is that if the first option value is set to a null value (“”) and the caption is set to any value, such as “*select item*”, the required flag is met and the control is allowed to pass a null regardless of whether a null is an accepted value or not. So the first option has to be set with both a null value and caption title. That worked fine for me.
Examples of the different formats for this control are provided by Carol over at her blog which can be found in the article “Listing Choices in RCDC Dropdowns”