Datagridview validating in specific column only

Private Sub DataGridView1_EditingControlShowing(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles DataGridView1.EditingControlShowing
        'source: http://www.devx.com/dotnet/Article/33748/1954?pf=true
        '---restrict inputs
        If DataGridView1.CurrentCell.ColumnIndex = 1 And Not e.Control Is Nothing Then
            Dim tb As TextBox = CType(e.Control, TextBox)
 
            '---add an event handler to the TextBox control---
            AddHandler tb.KeyPress, AddressOf TextBox_KeyPress
            AddHandler tb.TextChanged, AddressOf Textbox_TextChanged
        End If
    End Sub
 
---valdate integer and dot----
Private Sub TextBox_KeyPress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs)
     If Char.IsDigit(e.KeyChar) Or Asc(e.KeyChar) = 8 Or Asc(e.KeyChar) = 46 Then
         If Asc(e.KeyChar) = 46 Then
                If CType(sender, TextBox).Text.Contains(Chr(46)) Then
                    e.Handled = True
                Else
                    e.Handled = False
                End If
            Else
                e.Handled = False
            End If
        Else
            e.Handled = True
        End If
    End SubPrivate Sub TextBox_KeyPress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs)
     If Char.IsDigit(e.KeyChar) Or Asc(e.KeyChar) = 8 Or Asc(e.KeyChar) = 46 Then
         If Asc(e.KeyChar) = 46 Then
                If CType(sender, TextBox).Text.Contains(Chr(46)) Then
                    e.Handled = True
                Else
                    e.Handled = False
                End If
            Else
                e.Handled = False
            End If
        Else
            e.Handled = True
        End If
    End Sub
 
 
---if data more than 100 and dot validate---
Private Sub Textbox_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs)
 
        If (DataGridView1.Columns(1).HeaderText = "Percentage") Or (DataGridView1.Columns(1).HeaderText = "Value") Then
            If CDec(CType(sender, TextBox).Text.Trim = ".") Then
                MsgBox(". has to appear after an interger", MsgBoxStyle.Critical)
                CType(sender, TextBox).Text = ""
                CType(sender, TextBox).Focus()
            End If
        End If
 
        If (DataGridView1.Columns(1).HeaderText = "Percentage") Then
            If Not CType(sender, TextBox).Text.Trim.Length = 0 Then
                If CDec(CType(sender, TextBox).Text >= 100) Then
                    MsgBox("Percentage cannot exceeds 100", MsgBoxStyle.Critical)
                    CType(sender, TextBox).Text = ""
                End If
            End If
        End If
    End SubPrivate Sub Textbox_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs)
 
        If (DataGridView1.Columns(1).HeaderText = "Percentage") Or (DataGridView1.Columns(1).HeaderText = "Value") Then
            If CDec(CType(sender, TextBox).Text.Trim = ".") Then
                MsgBox(". has to appear after an interger", MsgBoxStyle.Critical)
                CType(sender, TextBox).Text = ""
                CType(sender, TextBox).Focus()
            End If
        End If
 
        If (DataGridView1.Columns(1).HeaderText = "Percentage") Then
            If Not CType(sender, TextBox).Text.Trim.Length = 0 Then
                If CDec(CType(sender, TextBox).Text >= 100) Then
                    MsgBox("Percentage cannot exceeds 100", MsgBoxStyle.Critical)
                    CType(sender, TextBox).Text = ""
                End If
            End If
        End If
    End Sub