Gridview compare current row to previous row

Question

I would like to format a gridview based on comparing the current row value (column 2) with the previous row value. So if they are the same the background color would be that same, say green. If they are not the same the background color would be red. For example:

Gridview values
Car 1 (bg color green)
Car 1 (bg color green)
Car 2 (bg color red)
Car 3 (bg color green)
Car 3 (bg color green)
Car 3 (bg color green)

I have not been able to get this to work. Here is the code I came up with.

Protected Sub GridView1_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GridView1.RowCreated

    If e.Row.RowType = DataControlRowType.DataRow Then

        If Not e.Row.DataItem Is Nothing Then

            'switch for first row 
            If e.Row.RowIndex = 1 Then
                Dim Gprev As GridViewRow = GridView1.Rows(e.Row.RowIndex - 1)
                If Gprev.Cells(1).Text = e.Row.Cells(1).Text Then
                    'e.Row.Cells(1).Text = ""
                    e.Row.BackColor = Drawing.Color.Red
                End If
            End If

            'now continue with the rest of the rows
            If e.Row.RowIndex > 1 Then

                'set reference to the row index and the current value
                Dim intC As Integer = e.Row.RowIndex
                Dim lookfor As String = e.Row.Cells(1).Text

                'now loop back through checking previous entries for matches 
                Do
                    Dim Gprev As GridViewRow = GridView1.Rows(intC - 1)

                    If Gprev.Cells(1).Text = e.Row.Cells(1).Text Then
                        'e.Row.Cells(1).Text = ""
                        e.Row.BackColor = Drawing.Color.Red
                    End If

                    intC = intC - 1
                Loop While intC > 0

            End If

        End If

    End If

End Sub

Solution 1

Code in c# but hopefully easy enough to translate...

In RowDataBound...

if (e.RowType != DataControlRowType.DataRow) return;  
if (e.Row.DataItemIndex ==0)  
{  
  e.Row.Cells[1].BackColor = Color.Green;  
  return;  
}  
var thisRow = e.Row;   
var prevRow = GridView.Rows[e.Row.DataItemIndex-1];  
e.Row.Cells[1].BackColor = (thisRow.Cells[1].Text == prevRow.Cells[1].Text) ? Color.Green : Color.Red;  
}

Note also green & red aren't generally good choices for contrast with each other (colour blindness)

Solution 2

Yet not tested but this should work or at least give you a hint:

Dim lastRowValue As String = ""

Protected Sub GridView1_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GridView1.RowCreated
    If e.Row.RowType = DataControlRowType.DataRow Then
        e.Row.BackColor = If(e.Row.Cells(1).Text = lastRowValue AndAlso
                             e.Row.RowIndex <> 0,
                             Drawing.Color.Red,
                             Drawing.Color.Green)
        lastRowValue = e.Row.Cells(1).Text
    End If
End Sub

Note that you've used GridView1_RowDataBound but handled GridView1.RowCreated in your sample.