how to custom the aggregate function

[Ocean Ju]

I read the example : http://demos.telerik.com/silverlight/#GridView/CustomAggregates and defined a class like this:

using System;
using Telerik.Windows.Data;
using System.Collections.Generic;
using System.Linq;

namespace MSHF.Paris.UIPlatform.Common
{
    public class ObjectSumFunction : EnumerableSelectorAggregateFunction
    {
        protected override string AggregateMethodName
        {
            get
            {
                return "Sum";
            }
        }

        protected override Type ExtensionMethodsType
        {
            get
            {
                return typeof(ObjectSum);
            }
        }
    }

    public static class ObjectSum
    {
        public static object Sum<TSource>(IEnumerable<TSource> source, Func<TSource, object> selector)
        {
            int itemCount = source.Count();
            if (itemCount > 0)
            {
                IEnumerable<decimal> values = from i in source select Convert.ToDecimal(selector(i));

                return values.Sum();
            }

            return 0;
        }
    }
}

add the function in code:
dataColumn.AggregateFunctions.Add(new ObjectSumFunction()
                        {
                            Caption = "total:",
                            SourceField = "A4",
                            SourceFieldType = typeof(object),
                            ResultFormatString = gd.GridColumnDefinitions[i].DataFormat
                        });

the column type is object(in fact, it is a decimal, but converted to object)

Get the error:No generic method 'Sum' on type 'MSHF.Paris.UIPlatform.Common.ObjectSum' is compatible with the", because it is a Just-In-Time Debugger dialog, the message is trucated.
please see the attached error file.

[Ocean Ju]

any suggestion?

[Igor]

Do you have tried this: 
Func<TSource, decimal> instead of  Func<TSource, Object> ?
I have the same problem with enum and string types. I don't know which types are available to the selector, but it seam that  string, Object and Enum aren't supported. This is a limitation in my project ,because my grid row data doesn't have numeric fields, only enums and strings. I have to add a dummy integer field only to make the function callable.
In my application I want to report how many rows are orangutan or chimpanzee counting the field ItemType grouped by location.
I use this code:

public static string CountPrimate<T>(IEnumerable<T> source
    , Func<T, int> selector) where T : PrimateViewModel
{
    int  oranCount = source.Count(x =>
        x.ItemType == PrimateTypeEnum.ORAN);

    int chimCount  = source.Count(x =>
        x.ItemType == PrimateTypeEnum.CHIM);

    return string.Format("Total Chimpanzee: {0}  Orangutan: {1}", chimCount, oranCount);
}

<telerik:GridViewDataColumn DataMemberBinding="{Binding ItemType}">
    <telerik:GridViewDataColumn.AggregateFunctions>
        <local:CountPrimateFunction Caption="" SourceField="DummyInt" />
    </telerik:GridViewDataColumn.AggregateFunctions>
</telerik:GridViewDataColumn>
...
<telerik:RadGridView.GroupDescriptors>
    <telerik:GroupDescriptor Member="Location.Name"  >
    </telerik:GroupDescriptor>
</telerik:RadGridView.GroupDescriptors>

The selector is not used because I don't have any integer fields (only the dummy one)  and using where T : PrimateViewModel 
 I can access to all source fields.  Returning a string I don't need the caption.
Why is the selector limited to numeric source fields? Is there a better way to solve this aggregation problem?

[Dimitrina]

Hi,

 If the custom aggregates do not work in your case, then I would recommend you to try the approach suggested in this forum thread.

Regards,
Didie
the Telerik team