很容易...你就错了，因为该事件的控制是不存在的：

Quite easy... You're doing it wrong, because by that event the control is not there:

protected void gv_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow && 
        (e.Row.RowState & DataControlRowState.Edit) == DataControlRowState.Edit)
    { 
        // Here you will get the Control you need like:
        DropDownList dl = (DropDownList)e.Row.FindControl("ddlPBXTypeNS");
    }
}

也就是说，它只会有效期为的DataRow （实际数据行），如果它在修改模式..因为你只有一次编辑一行。在 e.Row.FindControl（ddlPBXTypeNS）只能找到您想要的控制。

That is, it will only be valid for a DataRow (the actually row with data), and if it's in Edit mode... because you only edit one row at a time. The e.Row.FindControl("ddlPBXTypeNS") will only find the control that you want.