nullreferenceexception in gridview when header is clicked - vb.net

Question

In my DataGridView selectionChange i have this code, so when the row change the texbox also changes. the code below works, i click the row and it displays right, also when i press up/down arrows. My problem is when I click somwhere in the Header of the grid i have this nullreferenceexception error Object reference not set to an instance of an object.. I don't have idea how to handle it, since i down know what it returns.
Private Sub DataGridView1_SelectionChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGridView1.SelectionChanged
Dim index As Integer
index = DataGridView1.CurrentCell.RowIndex '<<<<--problem here when I click the header
If (index <= maxrows - 1) Or (index <> Nothing) Then
TextBox2.Text = DataGridView1.Item(1, index).Value()
TextBox3.Text = DataGridView1.Item(2, index).Value()
TextBox4.Text = DataGridView1.Item(3, index).Value()
End If
End Sub

Answer 1

A null reference is raised whenever you get the RowIndex wherein there is no ROW is selected.
Clicking the header calls SORT and this clears the selection.
This will help you get rid of the nullreference exception
If DatagridView1.SelectedRows.Count = 0 Then
Msgbox "Nothing Selected"
Exit Sub 'Trapping
End If
Code:
Private Sub DataGridView1_SelectionChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGridView1.SelectionChanged
If DatagridView1.SelectedRows.Count = 0 Then
Msgbox "Nothing Selected"
Exit Sub 'Trapping
End If
Dim index As Integer
With DataGridView
index = .CurrentRow.RowIndex
If (index <= maxrows - 1) Then
TextBox2.Text = .Item(1, index).Value()
TextBox3.Text = .Item(2, index).Value()
TextBox4.Text = .Item(3, index).Value()
End If
End With
End Sub