I'm working on a report which has these input parameters:

StartDate (textbox, data type is datetime)
EndDate (textbox, data type is datetime)
AccountNumber (dropdown, data type is string)

I need to set up logic where if the user viewing the report has input only date values, they'll be prompted to select an AccountNumber, or if they select an AccountNumber they'll be required to select a valid date range.

I've successfully created functions for purposes of validating the fields, and put these on the Code tab of the Report Properties, but now I'm not clear on how to make this work from the report itself.

Can I pop up a messagebox that fires if the user hasn't input the required info and they try to View the report? Or can I just populate a textbox with some error text like "Hey dummy, you forgot the AccountNumber"?