VirtualServerModeSource.ConfigurationChanged Event

Fires on initial data load and reload in the bound grid control, and when the data grid’s sort and filter configuration changes. Allows you to initialize the data source and (optionally) return an initial batch of records.

Namespace: DevExpress.Data

Assembly: DevExpress.Data.v23.2.dll

NuGet Package: DevExpress.Data

Declaration

C#

public event EventHandler<VirtualServerModeRowsEventArgs> ConfigurationChanged

VB.NET

Public Event ConfigurationChanged As EventHandler(Of VirtualServerModeRowsEventArgs)

Event Data

The ConfigurationChanged event's data class is VirtualServerModeRowsEventArgs. 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.
CurrentRowCount	Gets the count of rows currently loaded to the grid.
RowsTask	Gets or sets the task that returns requested rows.
UserData	Read this parameter to get custom data passed from the previously called Task or ConfigurationChanged event handler. When handling the VirtualServerModeSource.ConfigurationChanged event, set the UserData event parameter to pass custom data to a subsequent VirtualServerModeSource.MoreRows event handler (unless you specify the RowsTask event parameter).

Remarks

The ConfigurationChanged event fires in the following cases:

• data load on startup
• data reload (e.g., when calling the GridControl.RefreshDataSource method)
• when the data grid’s sort and filter configuration changes.

The ConfigurationChanged event allows you prepare your data for the load in the grid control, and optionally provide an initial batch of rows. To provide a batch of rows, create a Task that will return requested rows, and assign this task to the RowTask event parameter. To provide subsequent batches of rows (when required), handle the VirtualServerModeSource.MoreRows event.

You can provide an initial and subsequent batches of rows by handling a single event - VirtualServerModeSource.MoreRows. In this case, if you handle the ConfigurationChanged event, leave the event’s RowTask parameter set to null.

Tip

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

Example

This example demonstrates how to create a WinForms Grid Control and bind it to a virtual server mode source.

C#

using System.Windows.Forms;
using System.Collections.Generic;
using DevExpress.Data;
using DevExpress.XtraGrid;
using DevExpress.XtraEditors;

namespace DXApplication {
   public partial class Form1 : XtraForm {
       public Form1() {
            InitializeComponent();
            // Creates and initializes a virtual data source.
            VirtualServerModeSource virtualServerModeSource = new VirtualServerModeSource();
            virtualServerModeSource.RowType = typeof(Product);
            virtualServerModeSource.ConfigurationChanged += virtualServerModeSource_ConfigurationChanged;
            virtualServerModeSource.MoreRows += virtualServerModeSource_MoreRows;
            // Creates a grid control and binds it to the virtual data source.
            GridControl gridControl = new GridControl();
            gridControl.Parent = this;
            gridControl.Dock = DockStyle.Fill;
            gridControl.DataSource = virtualServerModeSource;
       }

       int batchSize = 20;
       int maxRowCount = 500;

       private void virtualServerModeSource_ConfigurationChanged(object sender, DevExpress.Data.VirtualServerModeRowsEventArgs e) {
           e.UserData = GetRows(0);
       }

       private void virtualServerModeSource_MoreRows(object sender, DevExpress.Data.VirtualServerModeRowsEventArgs e) {
           e.RowsTask = System.Threading.Tasks.Task.Factory.StartNew(() => {
               bool moreRows = e.CurrentRowCount < maxRowCount - batchSize;
               return new VirtualServerModeRowsTaskResult(GetRows(e.CurrentRowCount), moreRows, e.UserData);
           }, e.CancellationToken);
       }

       List<Product> GetRows(int startRowIndex) {
           List<Product> lst = new List<Product>();
           for (int i = startRowIndex; i < startRowIndex + batchSize; i++)
               lst.Add(new Product { ID = i, Name = $"Product{i}" });
           return lst;
       }
   }

   public class Product {
       public int ID { get; set; }
       public string Name { get; set; }
   }
}

VB.NET

Imports System.Windows.Forms
Imports System.Collections.Generic
Imports DevExpress.Data
Imports DevExpress.XtraGrid
Imports DevExpress.XtraEditors

Namespace DXApplication
   Public Partial Class Form1 Inherits XtraForm
       Public Sub New()
           InitializeComponent()
           Dim virtualServerModeSource As VirtualServerModeSource = New VirtualServerModeSource()
           virtualServerModeSource.RowType = GetType(Product)
           AddHandler virtualServerModeSource.ConfigurationChanged, AddressOf virtualServerModeSource_ConfigurationChanged
           AddHandler virtualServerModeSource.MoreRows, AddressOf virtualServerModeSource_MoreRows
           Dim gridControl As GridControl = New GridControl()
           gridControl.Parent = Me
           gridControl.Dock = DockStyle.Fill
           gridControl.DataSource = virtualServerModeSource
       End Sub
       Private batchSize As Integer = 20
       Private maxRowCount As Integer = 500
       Private Sub virtualServerModeSource_ConfigurationChanged(ByVal sender As Object, ByVal e As VirtualServerModeRowsEventArgs)
           e.UserData = GetRows(0)
       End Sub
       Private Sub virtualServerModeSource_MoreRows(ByVal sender As Object, ByVal e As VirtualServerModeRowsEventArgs)
           e.RowsTask = System.Threading.Tasks.Task.Factory.StartNew(Function()
               Dim moreRows = e.CurrentRowCount < maxRowCount - batchSize
               Return New VirtualServerModeRowsTaskResult(GetRows(e.CurrentRowCount), moreRows, e.UserData)
           End Function, e.CancellationToken)
       End Sub
       Private Function GetRows(ByVal startRowIndex As Integer) As List(Of Product)
           Dim lst As List(Of Product) = New List(Of Product)()
           For i = startRowIndex To startRowIndex + batchSize - 1
               lst.Add(New Product With {
                   .ID = i,
                   .Name = $"Product{i}"
               })
           Next
           Return lst
       End Function
   End Class
   Public Class Product
       Public Property ID As Integer
       Public Property Name As String
   End Class
End Namespace