I am designing a web application which consists of several modules, and for some of these modules the user must be able to select how many/which sources of data to display in the module.
I had originally decided to simply use radio buttons, with one radio button for each data source and one radio button for displaying every data source in the module (it is a requirement that the user can show only one or all).
However, the amount of available data sources can vary from 1 to x (x can be very high) depending on the user - and the radio buttons will do a good job if the user only has 3 data sources, but not so much if the user has 20 sources of data available.
I have considered showing radio buttons for user where amount of data sources are < 7, and using a drop down list for > 7 (we can check how many data sources are returned to the user), but I am afraid this can cause some inconsistency if the user for example one day goes from having 6 to 10 sources of data.
Another option could be displaying a radio button for selecting a single data source, with a dropdown list for this option - and a radio button for selecting every available data source.
Any suggestions on the best way of solving this?