I'm having some difficulty implementing the visibility of a rectangle and I used this line of code to set the visibility:
=IIF(Len(ReportItems!txtCountVolunteer.Value) > 0, true, false)
Unfortunately it doesn't work.
Good day to you as well.
It seems like that you have got the logic reversed in the expression. There is "Hidden" property for a rectangle, and note that there is no "Visible" property. So the expression for the rectangle's "Hidden" property should be:
=IIF(Len(ReportItems!txtCountVolunteer.Value) <= 0, true, false)