How to program using block interface that has code behind it

Question

Hi , I have a question.In some programs there are block which we can drag and enter parameters in it like in MATLAB simulink behind which the code is hidden. So that a user can just drag the block and conencts its output to another block that does some function. Can any body suggest how we can implement that in either VC++ ,C# or VB Thanks in advance, Rajesh