VirtualServerModeSource.MoreRows Event

Fires when a bound grid control asks the data source for a new batch of rows.

Namespace: DevExpress.Data

Assembly: DevExpress.Data.v23.2.dll

NuGet Package: DevExpress.Data

Declaration

C#

public event EventHandler<VirtualServerModeRowsEventArgs> MoreRows

VB.NET

Public Event MoreRows As EventHandler(Of VirtualServerModeRowsEventArgs)

Event Data

The MoreRows 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

To provide a batch of rows, create a Task that returns requested rows and assign it to the RowTask event parameter.

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+).

The VirtualServerModeSource supports two data supplying scenarios:

• Handle the VirtualServerModeSource.ConfigurationChanged event to perform a source initialization and supply an initial batch of rows. Handle the MoreRows event to supply subsequent batches of rows (when required).

• Handle the VirtualServerModeSource.ConfigurationChanged event to perform a source initialization (when required). Handle the MoreRows event to supply all (initial and subsequent) batches of rows. If you handle the VirtualServerModeSource.ConfigurationChanged event, this event’s RowTask parameter should be left unassigned.

  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