HtmlSelect.ServerChange Event

 
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Occurs when the selected items in the HtmlSelect control change between posts to the server.

Namespace:   System.Web.UI.HtmlControls
Assembly:  System.Web (in System.Web.dll)

public event EventHandler ServerChange

The ServerChange event is raised when the selected items in the HtmlSelect control change between posts to the server.

System_CAPS_noteNote

The control must have view state enabled for the ServerChange event to work correctly.

For more information about handling events, see NIB: Consuming Events.

The following code example demonstrates how to specify and code an event handler declaratively for the ServerChange event of the HtmlSelect control. The event handler determines whether the selected items are compatible with each other.

<%@ 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 /> &nbsp;&nbsp; -" + 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>

The following code example demonstrates how to specify and code an event handler programmatically for the ServerChange event of the HtmlSelect control. The event handler determines whether the selected items are compatible with each other.


<%@ 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 /> &nbsp;&nbsp; -" + 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>

.NET Framework
Available since 1.1
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