String Field Validation

Hi All,

I have a Custom screen with 2 buttons.

a.  "Add_Note" button

b.  "Navigate_Page2" button.

"Add_note" button navigates to page 1. Page1 has a input field "Note" of type String. On Click of  "Navigate_Page2" button in the Custom Screen, we have to validate if the "Note" input field is blank and pop up message should be provided. If not blank it should navigate to page2.

How will i check whether the field is blank and how to add a pop up inside an update / validation rule.

How to achieve this? Please help me with this issue.

Thanks,

Divya