e.Result throwing nullreferenceexception

Question

I am trying to use an On_Selecting event to populate linqdatasource, which is in turn use to supply data to a chart. When the event fires, e.Result throws a null reference exception. I haven't been able to figure this one out. Please help.

First, the code for the linqdatasource and the chart:

<asp:Chart ID="MonthlyChart"
           runat="server"
           DataSourceID="LinqGetChartData">
    <series>
        <asp:Series Label="#VALX, #VALY"
                    ChartType="Pie"
                    Name="Series1"
                    XValueMember="CostSum"
                    YValueMembers="SalesMonth"></asp:Series>
    </series>
    <chartareas>
        <asp:ChartArea Name="ChartArea1">
            <AxisY Title="Sales Month">
                <LabelStyle Format="MMMM" />
            </AxisY>
            <AxisX Title="Total"></AxisX>
            <Area3DStyle Enable3D="True"
                         WallWidth="10"></Area3DStyle>
        </asp:ChartArea>
    </chartareas>
</asp:Chart>
<asp:LinqDataSource ID="LinqGetChartData"
                    runat="server"
                    ContextTypeName="MegaChallengePapaBobsPizza.Persistence.CustomerEntities"
                    EntityTypeName=""
                    OnSelecting="LinqGetChartData_Selecting"
                    TableName="Customers"></asp:LinqDataSource>

Next, the code for the On_Selecting event:

protected void LinqGetChartData_Selecting(object sender, LinqDataSourceSelectEventArgs e)
{
    var customerList = Domain.CustomerManager.GetCustomers();
    var query = customerList.OrderBy(c => c.OrderDate)
                            .GroupBy(c => c.OrderDate.ToString("MMMM"),
                            (c => c.Cost),
                            (groupKey, totCost) => new SalesResult()
                            {
                                 SalesMonth = groupKey,
                                 CostSum = totCost.Sum()
                            });
    e.Result = query;
}

Finally, the code that fires the event:

LinqGetChartData_Selecting(sender, e as LinqDataSourceSelectEventArgs);

Any help would be much appreciated. Thanks.

Looks like e isn't an object of type LinqDataSourceSelectEventArgs. Where is LinqGetChartData_Selecting called from? — H77, Nov 10 '16 at 03:29
@DwightMendoza why are you calling it from Page_Load? You shouldn't need to since the event handler is assigned in the asp. — H77, Nov 10 '16 at 04:48

score 0 · Accepted Answer · answered Nov 10 '16 at 04:55

0

Since you're calling the event handler in the Page_Load event I assume the variable "e" that you're using is the EventArgs parameter of the Page_Load event. This parameter isn't of type LinqDataSourceSelectEventArgs which results in the following returning null.

e as LinqDataSourceSelectEventArgs

When you try to access the property "Result" of null the null reference exception is thrown.

Since the event handler is assigned in the asp code to the LinqDataSource object you shouldn't need to call it again within Page_Load, unless you have a special reason to do so?

answered Nov 10 '16 at 04:55

H77

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I took it out of the Page_Load and now I don't get the null reference, but still the pie chart is not appearing. Any ideas? – Pismotality Nov 10 '16 at 05:13
Try calling databind on the chart in your code behind Page_Load. – H77 Nov 10 '16 at 05:16
That didn't work. – Pismotality Nov 10 '16 at 05:22
I don't think this matters but does it make a difference if you move the datasource above the chart? – H77 Nov 10 '16 at 05:34
Moving the datasource made no difference. – Pismotality Nov 10 '16 at 06:13

e.Result throwing nullreferenceexception

1 Answers1