Press "@" and drop out ComboBox. [WITH#]

Question

First of all, I'm sorry if this happens again, but I did not find anything about it. Is it possible in C # to press a specific key in a TextBox, in this case "@" and display a list of names?

Same as FB and Whatsapp. To save time, if you press @, a list of people will appear, and if you continue to enter text, the list is sorted until you find the name you need.