HtmlSelect.ServerChange Evento

Referencia

Definición

Espacio de nombres:: System.Web.UI.HtmlControls

Ensamblado:: System.Web.dll

Importante

Parte de la información hace referencia a la versión preliminar del producto, que puede haberse modificado sustancialmente antes de lanzar la versión definitiva. Microsoft no otorga ninguna garantía, explícita o implícita, con respecto a la información proporcionada aquí.

Se produce cuando los elementos seleccionados del control HtmlSelect cambian entre cada envío al servidor.

public:
 event EventHandler ^ ServerChange;

public event EventHandler ServerChange;

member this.ServerChange : EventHandler

Public Custom Event ServerChange As EventHandler

Tipo de evento

EventHandler

Ejemplos

En el ejemplo de código siguiente se muestra cómo especificar y codificar un controlador de eventos mediante declaración para el ServerChange evento del HtmlSelect control. El controlador de eventos determina si los elementos seleccionados son compatibles entre sí.

<%@ Page Language="C#" AutoEventWireup="True" %>

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

<script runat="server">

    void Button_Click (Object sender, EventArgs e)
    {
        Label1.Text = "You selected:";

        for (int i=0; i<=Select1.Items.Count - 1; i++)
        {
           if (Select1.Items[i].Selected)
               Label1.Text += "<br />    -" + Select1.Items[i].Text;      
        }

    }

    void Server_Change (Object sender, EventArgs e)
    {
        int Count = 0;

        for (int i=0; i<=Select1.Items.Count - 1; i++)
        {
           if (Select1.Items[i].Selected)
               Count++;      
        }

        if ((Count > 1) && (Select1.Items[0].Selected))
            Label2.Text = "Hey! You can't select 'All' with another selection!!";
        else
            Label2.Text = "";
    }

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title> HtmlSelect Example </title>
</head>

<body>

   <form id="form1" runat="server">

      <h3> HtmlSelect Example </h3>

      Select items from the list: <br /><br />

      <select id="Select1" 
              multiple="true"
              onserverchange="Server_Change"
              runat="server">

         <option value="All"> All </option>
         <option value="1" selected="selected"> Item 1 </option>
         <option value="2"> Item 2 </option>
         <option value="3"> Item 3 </option>
         <option value="4"> Item 4 </option>
         <option value="5"> Item 5 </option>
         <option value="6"> Item 6 </option>

      </select>

      <br /><br />

      <button id="Button1"
              onserverclick="Button_Click"
              runat="server">

         Submit

      </button>

      <br /><br />

      <asp:Label id="Label1"
           runat="server"/>

      <br />

      <asp:Label id="Label2"
           runat="server"/>

   </form>

</body>

</html>

<%@ Page Language="VB" AutoEventWireup="True" %>

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

<script runat="server">

    Sub Button_Click (sender As Object, e As EventArgs)
        Dim i As Integer

        Label1.Text = "You selected:"
        For i = 0 to Select1.Items.Count - 1
           If Select1.Items(i).Selected Then
               Label1.Text = Label1.Text & "<br />    -" & Select1.Items(i).Text
           End If         
        Next
    End Sub

    Sub Server_Change (sender As Object, e As EventArgs)
        Dim i As Integer
        Dim Count As Integer = 0

        For i = 0 to Select1.Items.Count - 1
            If Select1.Items(i).Selected Then
                Count = Count + 1
            End If         
        Next

        If Count > 1 And Select1.Items(0).Selected Then
            Label2.Text = "Hey! You can't select 'All' with another selection!!"
        Else
            Label2.Text = ""
        End If
    End Sub

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title> HtmlSelect Example </title>
</head>
<body>
<form id="form1" runat="server">
   <div>

      <h3> HtmlSelect Example </h3>

      Select items from the list: <br /><br />

      <select id="Select1" 
              multiple="true"
              onserverchange="Server_Change"
              runat="server">

         <option value="All"> All </option>
         <option value="1" selected="selected"> Item 1 </option>
         <option value="2"> Item 2 </option>
         <option value="3"> Item 3 </option>
         <option value="4"> Item 4 </option>
         <option value="5"> Item 5 </option>
         <option value="6"> Item 6 </option>

      </select>

      <br /><br />

      <button id="Button1"
              onserverclick="Button_Click"
              runat="server">

         Submit

      </button>

      <br /><br />

      <asp:Label id="Label1"
           runat="server"/>

      <br />

      <asp:Label id="Label2" runat="server"/>

   </div>
</form>
</body>
</html>

En el ejemplo de código siguiente se muestra cómo especificar y codificar un controlador de eventos mediante programación para el ServerChange evento del HtmlSelect control. El controlador de eventos determina si los elementos seleccionados son compatibles entre sí.


<%@ Page Language="C#" %>

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

<script runat="server">
    void Button_Click (Object sender, EventArgs e)
    {
        // Display the selected items.
        Label1.Text = "You selected:";

        for (int i=0; i<=Select1.Items.Count - 1; i++)
        {
            if (Select1.Items[i].Selected)
                Label1.Text += "<br />    -" + Select1.Items[i].Text;      
        }
    }

    void Server_Change(Object sender, EventArgs e)
    {
        // The ServerChange event is commonly used for data validation.
        // This method will display a warning if the "All" option is  
        // selected in combination with another item in the list.
        int Count = 0;

        // Determine the number of selected items in the list.
        for (int i=0; i<=Select1.Items.Count - 1; i++)
        {
            if (Select1.Items[i].Selected)
                Count++;      
        }

        // Display an error message if more than one item is selected with
        // the "All" item selected.
        if ((Count > 1) && (Select1.Items[0].Selected))
            Label2.Text = "Hey! You can't select 'All' with another selection!!";
        else
            Label2.Text = "";
    }

    void Page_Load(Object sender, EventArgs e)
    {
        // Create an EventHandler delegate for the method you want to
        // handle the event, and then add it to the list of methods
        // called when the event is raised.
        Select1.ServerChange += new System.EventHandler(this.Server_Change);
        Button1.ServerClick += new System.EventHandler(this.Button_Click);
    }

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title> HtmlSelect Server Change Example </title>
</head>
<body>
<form id="form1" runat="server">
   <div>

      <h3> HtmlSelect Server Change Example </h3>

      Select items from the list: <br /><br />

      <select id="Select1" 
              multiple="true"
              runat="server">

         <option value="All"> All </option>
         <option value="1" selected="selected"> Item 1 </option>
         <option value="2"> Item 2 </option>
         <option value="3"> Item 3 </option>
         <option value="4"> Item 4 </option>
         <option value="5"> Item 5 </option>
         <option value="6"> Item 6 </option>

      </select>

      <br /><br />

      <button id="Button1"
              runat="server">

         Submit

      </button>

      <br /><br />

      <asp:Label id="Label1"
           runat="server"/>

      <br />

      <asp:Label id="Label2"
           runat="server"/>

   </div>
</form>
</body>
</html>


<%@ Page Language="VB" %>

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

<script runat="server">

    Sub Button_Click (sender As Object, e As EventArgs)
        ' Display the selected items.
        Label1.Text = "You selected:"

        Dim i As Integer

        For i=0 To Select1.Items.Count - 1
            If Select1.Items(i).Selected Then
                Label1.Text &= "<br />    -" & Select1.Items(i).Text
            End If      
        Next
    End Sub

    Sub Server_Change(sender As Object, e As EventArgs)
        ' The ServerChange event is commonly used for data validation.
        ' This method will display a warning if the "All" option is 
        ' selected in combination with another item in the list.
        Dim Count As Integer = 0
        Dim i As Integer

        ' Determine the number of selected items in the list.
        For i=0 To Select1.Items.Count - 1
            If Select1.Items(i).Selected Then
                Count = Count + 1      
            End If
        Next

        ' Display an error message if more than one item is selected with
        ' the "All" item selected.
        If ((Count > 1) And (Select1.Items(0).Selected)) Then
            Label2.Text = "Hey! You can't select 'All' with another selection!!"
        Else
            Label2.Text = ""
        End If
    End Sub

    Sub Page_Load(sender As Object, e As EventArgs)
        ' Create an EventHandler delegate for the method you want to 
        ' handle the event, and then add it to the list of methods
        ' called when the event is raised.
        AddHandler Select1.ServerChange, AddressOf Server_Change
        AddHandler Button1.ServerClick, AddressOf Button_Click
    End Sub

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title> HtmlSelect ServerChange Example </title>
</head>
<body>
<form id="form1" runat="server">
   <div>

      <h3> HtmlSelect ServerChange Example </h3>

      Select items from the list: <br /><br />

      <select id="Select1" 
              multiple="true"
              runat="server">

         <option value="All"> All </option>
         <option value="1" selected="selected"> Item 1 </option>
         <option value="2"> Item 2 </option>
         <option value="3"> Item 3 </option>
         <option value="4"> Item 4 </option>
         <option value="5"> Item 5 </option>
         <option value="6"> Item 6 </option>

      </select>

      <br /><br />

      <button id="Button1"
              runat="server">

         Submit

      </button>

      <br /><br />

      <asp:Label id="Label1"
           runat="server"/>

      <br />

      <asp:Label id="Label2"
           runat="server"/>

   </div>
</form>
</body>
</html>

Comentarios

El ServerChange evento se genera cuando los elementos seleccionados del HtmlSelect control cambian entre publicaciones al servidor.

Nota

El control debe tener habilitado el estado de vista para que el ServerChange evento funcione correctamente.

Para obtener más información acerca de cómo controlar eventos, vea controlar y provocar eventos.

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