Hi Rohit,
Below way you will get the selected item and value of the dropdown.
Dim ddllist As DropDownList = DirectCast(sender, DropDownList)
Dim ddltype As DropDownList = TryCast(ddllist.NamingContainer.FindControl("cmbShowName"), DropDownList)
Dim selectedText As String = ddltype.SelectedItem.Text
Dim selectedValue As String = ddltype.SelectedValue
Or simply change from
Dim item As DataGridItem = DirectCast(cell.Parent, DataGridItem)
to
Dim item As GridViewRow = DirectCast(cell.Parent, GridViewRow)