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Code-Behind

It can be desirable to separate the code content of a page completely from the HTML and other text, layout or graphical information by placing it in a separate file. In ASP.NET parlance, this technique is known as code-behind.

[DYALOG]\Samples\asp.net\tutorial\intro5.aspx illustrates this technique. 

<%@Page Language="Dyalog" Inherits="FruitSelection" src="fruit.apl" %>
<%@Register TagPrefix="tutorial" Namespace="Tutorial" Assembly="tutorial" %>
<html>
<head>
<title>Code behind: separating your code from the page layout</title>
<link rel="stylesheet" type="text/css" href="apl.css">
</head>
<body>
<h1>intro5: Code Behind</h1>
<p>This example illustrates how you can separate your code from the page layout.</p>
<form  runat="server" >
<asp:DropDownList id="list"
    runat="server"
    autopostback="true"
    OnSelectedIndexChanged="Select"/>
<p><asp:Label id="out" runat="server" /></p>
</form>
</body>
<tutorial:index runat="server"/>
</html>

This example is intended to be run in the framework of the tutorial; the two lines of code that refer to this framework (they each contain the word "tutorial") should be ignored.

The statement: 

%@Page Language="Dyalog" Inherits="FruitSelection" src="fruit.apl" %>

says that this page, when compiled, should inherit from a class called FruitSelection; this class is written in the "Dyalog" language, and its source code resides in a file called fruit.apl. FruitSelection is effectively the base class for the .aspx page.

In this example, fruit.apl is another text file containing the code and comprises: 

:Class FruitSelection: System.Web.UI.Page
:Using System

∇Page_Load
:Access Public
:if 0=IsPostBack
    list.Items.Add ⊂'Pears'
    list.Items.Add ⊂'Nectarines'
    list.Items.Add ⊂'Strawberries'
:endif
∇

∇Select args
:Access public
:Signature Select Object,EventArgs
out.Text←'You selected ',list.SelectedItem.Text
∇
:EndClass

The file requires :Class and :EndClass statements. These tell the Dyalog .NET Compiler the name of the class being defined and the name of its base class. When the source code is in a .aspx file, this information is provided automatically by the Dyalog .NET Compiler.

The name of the class (in this case, FruitSelection) must be the same name as is referenced in the .aspx web page file (intro5.aspx). The base class must be System.Web.UI.Page.

The body of the script is the same as the script section in the example in [DYALOG]\Samples\asp.net\tutorial\intro3.aspx (see The Page_Load Event) – only the names of the fruit have been changed so that it is clear which example is being executed.