I need to create an application in VB .Net where the user will enter the reason to their appointment in a textbox and the time from a combo box. Upon entering the info and selecting a time, they enter these information through a button click event. I have two listbox where the first one stores the reason for the appointment and the second one stores the time. Now, I don't want them to enter two appointments at the same time. If they do so, I want to throw an error message saying "The appointment at this time already exists. Any help??
This is what I tried so far:
Under button1_Click event
But i don't know know how would I check to throw an error message if they have two appointments at the same time.