How to create a function to hide rows based on a cell value in VBA EXCEL

Question

I created this function to hide some rows based on a cell value.

Function myTest(Unit As String)
ThisWorkbook.Worksheets("TESTING").Rows("15:16").Select
    If Unit = "XXX" Then
        Selection.EntireRow.Hidden = True
    Else
        Selection.EntireRow.Hidden = False
        myTest= "1"
    End If
End Function

When the unit value is not "XXX" the functions works fine, but when it is "XXX", the cell that calls this function gets #VALUE!

Answer 1

If you care about returning whether the cells are now hidden, then you can keep it as a function. Otherwise make it a Sub and get rid of the myTest = ... line below. Selecting cells in VBA is almost always an awful idea. It is unreliable, buggy, and a huge slowdown. The following code is the most concise function I can give you to do this. It directly applies the True/False evaluation of Unit = "XXX" to the Hidden property of the rows. I added an explicit Boolean return type.

Function myTest(Unit As String) As Boolean
    ThisWorkbook.Worksheets("Sheet5").Rows("15:16").EntireRow.Hidden = (Unit = "XXX")
    myTest = Not (Unit = "XXX")
End Function

To stay closer to your structure you could use a range object:

Function myTest(Unit As String) As String
    Dim rng As Range
    rng = ThisWorkbook.Worksheets("TESTING").Rows("15:16")
    If Unit = "XXX" Then
        rng.EntireRow.Hidden = True
        myTest = "0"
    Else
        rng.EntireRow.Hidden = False
        myTest= "1"
    End If
End Function

Or you could use a With block:

Function myTest(Unit As String) As String
    With ThisWorkbook.Worksheets("TESTING").Rows("15:16")
        If Unit = "XXX" Then
            .EntireRow.Hidden = True
            myTest = "0"
        Else
            .EntireRow.Hidden = False
            myTest= "1"
        End If
    End With
End Function