DataGrid.VirtualItemCount DataGrid.VirtualItemCount DataGrid.VirtualItemCount DataGrid.VirtualItemCount Property

Definizione

Ottiene o imposta il numero virtuale di elementi nel controllo DataGrid quando si utilizza lo spostamento personalizzato.Gets or sets the virtual number of items in the DataGrid control when custom paging is used.

public:
 virtual property int VirtualItemCount { int get(); void set(int value); };
[System.ComponentModel.Browsable(false)]
public virtual int VirtualItemCount { get; set; }
member this.VirtualItemCount : int with get, set
Public Overridable Property VirtualItemCount As Integer

Valore della proprietà

Il numero virtuale di elementi nel controllo DataGrid quando si utilizza lo spostamento personalizzato.The virtual number of items in the DataGrid control when custom paging is used.

Eccezioni

Il valore specificato è un numero negativo.The specified value is a negative number.

Esempi

Esempio di codice seguente viene illustrato come utilizzare il VirtualItemCount proprietà per specificare il numero totale di elementi nel DataGrid controllare quando viene utilizzato il paging personalizzato.The following code example demonstrates how to use the VirtualItemCount property to specify the total number of items in the DataGrid control when custom paging is used.

<%@ Page Language="C#" AutoEventWireup="True" %>
<%@ Import Namespace="System.Data" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >

   <script runat="server">

      // Normally, an entire data source is loaded in the DataGrid control, 
      // which can take up a lot of resources. This example uses custom 
      // paging, which loads only the segment of data needed to fill a
      // single page. In order to query for the appropriate segment of
      // data, the index of the first item displayed on a page must be
      // tracked as the user navigates between pages.
      int startIndex = 0;

      ICollection CreateDataSource() 
      {

         // Create sample data for the DataGrid control.
         DataTable dt = new DataTable();
         DataRow dr;

         // Define the columns of the table.
         dt.Columns.Add(new DataColumn("IntegerValue", typeof(Int32)));
         dt.Columns.Add(new DataColumn("StringValue", typeof(string)));
         dt.Columns.Add(new DataColumn("DateTimeValue", typeof(string)));
         dt.Columns.Add(new DataColumn("BoolValue", typeof(bool)));

         // Populate the table with sample values. When using custom paging,
         // a query should only return enough data to fill a single page, 
         // beginning at the start index.
         for (int i = startIndex; i < (startIndex + MyDataGrid.PageSize); i++) 
         {
             dr = dt.NewRow();

             dr[0] = i;
             dr[1] = "Item " + i.ToString();
             dr[2] = DateTime.Now.ToShortDateString();
             dr[3] = (i % 2 != 0) ? true : false;

             dt.Rows.Add(dr);
         }

         DataView dv = new DataView(dt);
         return dv;

      }

      void Page_Load(Object sender, EventArgs e) 
      {

         // Load sample data only once, when the page is first loaded.
         if (!IsPostBack) 
         {

            // Set the virtual item count, which specifies the total number
            // items displayed in the DataGrid control when custom paging
            // is used.
            MyDataGrid.VirtualItemCount = 200;

            // Retrieve the segment of data to display on the page from the
            // data source and bind it to the DataGrid control.
            BindGrid();

         }

      }

      void MyDataGrid_Page(Object sender, DataGridPageChangedEventArgs e) 
      {

         // For the DataGrid control to navigate to the correct page when
         // paging is allowed, the CurrentPageIndex property must be updated
         // programmatically. This process is usually accomplished in the
         // event-handling method for the PageIndexChanged event.

         // Set CurrentPageIndex to the page the user clicked.
         MyDataGrid.CurrentPageIndex = e.NewPageIndex;

         // Calculate the index of the first item to display on the page 
         // using the current page index and the page size.
         startIndex = MyDataGrid.CurrentPageIndex * MyDataGrid.PageSize;

         // Retrieve the segment of data to display on the page from the 
         // data source and bind it to the DataGrid control.
         BindGrid();

      }

      void BindGrid() 
      {

         MyDataGrid.DataSource = CreateDataSource();
         MyDataGrid.DataBind();

      }

   </script>

<head runat="server">
    <title> DataGrid Custom Paging Example </title>
</head>
<body>

   <form id="form1" runat="server">
 
      <h3> DataGrid Custom Paging Example </h3>

      <asp:DataGrid id="MyDataGrid" 
           AllowCustomPaging="True" 
           AllowPaging="True" 
           PageSize="10" 
           OnPageIndexChanged="MyDataGrid_Page" 
           runat="server">

         <HeaderStyle BackColor="Navy" 
                      ForeColor="White" 
                      Font-Bold="True" />

         <PagerStyle Mode="NumericPages" 
                     HorizontalAlign="Right" />

      </asp:DataGrid>

   </form>

</body>
</html>

<%@ Page Language="VB" AutoEventWireup="True" %>
<%@ Import Namespace="System.Data" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >

   <script runat="server">

      ' Normally, an entire data source is loaded in the DataGrid control, 
      ' which can take up a lot of resources. This example uses custom 
      ' paging, which loads only the segment of data needed to fill a
      ' single page. In order to query for the appropriate segment of
      ' data, the index of the first item displayed on a page must be
      ' tracked as the user navigates between pages.
      Dim startIndex As Integer = 0

      Function CreateDataSource() As ICollection 

         ' Create sample data for the DataGrid control.
         Dim dt As DataTable = New DataTable()
         Dim dr As DataRow

         ' Define the columns of the table.
         dt.Columns.Add(New DataColumn("IntegerValue", GetType(Int32)))
         dt.Columns.Add(New DataColumn("StringValue", GetType(String)))
         dt.Columns.Add(New DataColumn("DateTimeValue", GetType(String)))
         dt.Columns.Add(New DataColumn("BoolValue", GetType(Boolean)))

         ' Populate the table with sample values. When using custom paging,
         ' a query should only return enough data to fill a single page, 
         ' beginning at the start index.
         Dim i As Integer         

         For i = startIndex To ((startIndex + MyDataGrid.PageSize) - 1) 

             dr = dt.NewRow()

             dr(0) = i
             dr(1) = "Item " & i.ToString()
             dr(2) = DateTime.Now.ToShortDateString()
             If (i Mod 2 <> 0) Then
                dr(3) = True
             Else
                dr(3) = False
             End If

             dt.Rows.Add(dr)

         Next i

         Dim dv As DataView = New DataView(dt)
         Return dv

      End Function

      Sub Page_Load(sender As Object, e As EventArgs) 

         ' Load sample data only once, when the page is first loaded.
         If Not IsPostBack Then 

            ' Set the virtual item count, which specifies the total number
            ' items displayed in the DataGrid control when custom paging
            ' is used.
            MyDataGrid.VirtualItemCount = 200

            ' Retrieve the segment of data to display on the page from the 
            ' data source and bind it to the DataGrid control.
            BindGrid()

         End If

      End Sub

      Sub MyDataGrid_Page(sender as Object, e As DataGridPageChangedEventArgs) 

         ' For the DataGrid control to navigate to the correct page when
         ' paging is allowed, the CurrentPageIndex property must be updated
         ' programmatically. This process is usually accomplished in the
         ' event-handling method for the PageIndexChanged event.

         ' Set CurrentPageIndex to the page the user clicked.
         MyDataGrid.CurrentPageIndex = e.NewPageIndex

         ' Calculate the index of the first item to display on the page 
         ' using the current page index and the page size.
         startIndex = MyDataGrid.CurrentPageIndex * MyDataGrid.PageSize

         ' Retrieve the segment of data to display on the page from the 
         ' data source and bind it to the DataGrid control.
         BindGrid()

      End Sub

      Sub BindGrid() 

         MyDataGrid.DataSource = CreateDataSource()
         MyDataGrid.DataBind()

      End Sub

   </script>

<head runat="server">
    <title> DataGrid Custom Paging Example </title>
</head>
<body>

   <form id="form1" runat="server">
 
      <h3> DataGrid Custom Paging Example </h3>

      <asp:DataGrid id="MyDataGrid" 
           AllowCustomPaging="True" 
           AllowPaging="True" 
           PageSize="10" 
           OnPageIndexChanged="MyDataGrid_Page" 
           runat="server">

         <HeaderStyle BackColor="Navy" 
                      ForeColor="White" 
                      Font-Bold="True" />

         <PagerStyle Mode="NumericPages" 
                     HorizontalAlign="Right" />

      </asp:DataGrid>

   </form>

</body>
</html>

Commenti

Utilizzare questa proprietà per specificare il numero virtuale di elementi di DataGrid controllare quando viene utilizzato il paging personalizzato.Use this property to specify the virtual number of items in the DataGrid control when custom paging is used. Questa proprietà viene utilizzato solo quando la AllowCustomPaging è impostata su true.This property is only used when the AllowCustomPaging property is set to true.

Se il AllowCustomPaging è impostata su true, il numero di pagine necessarie per visualizzare tutti gli elementi la DataGrid controllo viene calcolato in base ai valori del PageSize e VirtualItemCount proprietà.If the AllowCustomPaging property is set to true, the number of pages required to display every item in the DataGrid control is calculated based on the values of the PageSize and VirtualItemCount properties.

Se il AllowCustomPaging è impostata su false, il numero di pagine visualizzate nel DataGrid controllo viene calcolato in base ai valori del PageSize proprietà e il numero totale di elementi nell'origine dati.If the AllowCustomPaging property is set to false, the number of pages displayed in the DataGrid control is calculated based on the values of the PageSize property and the total number of items in the data source.

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