To get the cell value, you need to read it directly from DataGridView1
using e.RowIndex
and e.ColumnIndex
properties.
Eg:
Private Sub DataGridView1_CellContentClick(ByVal sender As System.Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridView1.CellContentClick
Dim value As Object = DataGridView1.Rows(e.RowIndex).Cells(e.ColumnIndex).Value
If IsDBNull(value) Then
TextBox1.Text = "" ' blank if dbnull values
Else
TextBox1.Text = CType(value, String)
End If
End Sub