Question

I am writing asp.net project in C# and I have a litle problem.

I have a dropdownlist inside gridview and both of them initially is filled from one database but different tables(different select queries).

I want to set ToolTip for dropdownlist from query which is used to fill gridview(DataTable1) by following code:

  <asp:TemplateField HeaderText="choose supervisor"  ItemStyle-Width="100px">
                 <ItemTemplate>                
                       <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true"                 
 OnSelectedIndexChanged="ddlTest_SelectedIndexChanged"
 ToolTip =<%#((DataSet1.DataTable1Row)(((DataRowView)Container.DataItem).Row)).p_id %>>
                       </asp:DropDownList>
                  </ItemTemplate>                
            </asp:TemplateField> 

but when I try run the project I get the following error:

Object reference not set to an instance of an object.

If I try set Tooltip manually, for example:

ToolTip = "abc"

the project runs without any problem.

Does someone know how to set tooltip for dropdownlist from database query?
Thanks.

Answer 1

I would do that from GridView’s RowDataBound event which is triggered for every GridViewRow but only when the GridView gets databound.

protected void GridView1_RowDataBound(Object sender, GridViewRowEventArgs e)
{
    var grid = (GridView)sender;
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        DropDownList DropDownList1 = (DropDownList)e.Row.FindControl("DropDownList1");
        DataRowView drv = (DataRowView)e.Row.DataItem;
        DataSet ds = drv.Row.Table.DataSet;
        // i'm not 100% sure what you need here, for example:
        DropDownList1.ToolTip = drv.Row.Field<int>("p_id").ToString();
    }
}

This is much more readable and easier to maintain and debug.