VirtualServerModeSource.TotalSummary Event

Fires when a grid control asks the data source to calculate total summaries.

Namespace: DevExpress.Data

Assembly: DevExpress.Data.v23.2.dll

NuGet Package: DevExpress.Data

Declaration

C#

public event EventHandler<VirtualServerModeTotalSummaryEventArgs> TotalSummary

VB.NET

Public Event TotalSummary As EventHandler(Of VirtualServerModeTotalSummaryEventArgs)

Event Data

The TotalSummary event's data class is VirtualServerModeTotalSummaryEventArgs. The following properties provide information specific to this event:

Property	Description
CancellationToken	Gets a token that allows you to respond to a task cancellation request invoked by the grid control.
ConfigurationInfo	Gets information on the grid’s current sorting, filtering and summary configuration.
NotReadyObject	This member supports the internal infrastructure.
TotalSummaryTask	Gets or sets the task that returns the requested summary value.

The event data class exposes the following methods:

Method	Description
NotifyIntermediateSummaryReady(IDictionary<ServerModeSummaryDescriptor, Object>)
NotifySummaryReady(IDictionary<ServerModeSummaryDescriptor, Object>)	Allows you to update the bound grid control with intermediate summary values.

Remarks

To supply the requested total summary values, create a Task that calculates these values and assign it to the VirtualServerModeTotalSummaryEventArgs.TotalSummaryTask event parameter. Use the VirtualServerModeTotalSummaryEventArgs.ConfigurationInfo parameter to identify the requested summaries.

You can provide the bound grid with intermediate summary results during the task execution. To accomplish this, call the VirtualServerModeTotalSummaryEventArgs.NotifyIntermediateSummaryReady method from the Task.

The created Task must return final values for all requested summaries, including those whose intermediate values are supplied with the NotifyIntermediateSummaryReady method.

Tip

A Task typically executes asynchronously. To return summary values synchronously, create the task with the Task.FromResult method (available in .NET Framework 4.5+).

Example

This example demonstrates how to handle the TotalSummary event to calculate the total summaries.

C#

using using DevExpress.Data;
using using DevExpress.Data.Filtering;
using using System.Collections.Generic;

private void VirtualServerModeSource1_TotalSummary(object sender, VirtualServerModeTotalSummaryEventArgs e) {
    e.TotalSummaryTask = new System.Threading.Tasks.Task<IDictionary<ServerModeSummaryDescriptor, object>>(GetSummaries, e.ConfigurationInfo.TotalSummary);
}

IDictionary<ServerModeSummaryDescriptor, object> GetSummaries(object descriptors) {
    Dictionary<ServerModeSummaryDescriptor, object> results = new Dictionary<ServerModeSummaryDescriptor, object>();
    int i = 0;
    foreach (ServerModeSummaryDescriptor descriptor in descriptors as ServerModeSummaryDescriptor[]) {
        results.Add(descriptor, GetSummary(descriptor.SummaryPropertyName, descriptor.SummaryType, i++));
    }
    return results;
}

object GetSummary(string fieldName, Aggregate summaryType, int index) {
    if (fieldName == "ID" && summaryType == Aggregate.Sum && index == 0)
        return 5;
    if (fieldName == "ID" && summaryType == Aggregate.Avg && index == 1)
        return 10;
    if (fieldName == "ID" && summaryType == Aggregate.Avg && index == 2)
        return 15;
    return null;
}

VB.NET

Imports using DevExpress.Data
Imports using DevExpress.Data.Filtering
Imports using System.Collections.Generic

Private Sub VirtualServerModeSource1_TotalSummary(ByVal sender As Object, ByVal e As VirtualServerModeTotalSummaryEventArgs)
    e.TotalSummaryTask = New System.Threading.Tasks.Task(Of IDictionary(Of ServerModeSummaryDescriptor, Object))(AddressOf GetSummaries, e.ConfigurationInfo.TotalSummary)
End Sub

Private Function GetSummaries(ByVal descriptors As Object) As IDictionary(Of ServerModeSummaryDescriptor, Object)
    Dim results As New Dictionary(Of ServerModeSummaryDescriptor, Object)()
    Dim i As Integer = 0
    For Each descriptor As ServerModeSummaryDescriptor In TryCast(descriptors, ServerModeSummaryDescriptor())
        results.Add(descriptor, GetSummary(descriptor.SummaryPropertyName, descriptor.SummaryType, i))
        i += 1
    Next descriptor
    Return results
End Function

Private Function GetSummary(ByVal fieldName As String, ByVal summaryType As Aggregate, ByVal index As Integer) As Object
    If fieldName = "ID" AndAlso summaryType Is Aggregate.Sum AndAlso index = 0 Then
        Return 5
    End If
    If fieldName = "ID" AndAlso summaryType Is Aggregate.Avg AndAlso index = 1 Then
        Return 10
    End If
    If fieldName = "ID" AndAlso summaryType Is Aggregate.Avg AndAlso index = 2 Then
        Return 15
    End If
    Return Nothing
End Function