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The SimpleCtl Control

The SimpleCtl Class is illustrated below: 

:Class SimpleCtl: Control                       
:Access public                                  
:Using System                                   
:Using System.Collections.Specialized,System.dll
:Using System.Web,System.Web.dll                
:Using System.Web.UI                            
:Using System.Web.UI.WebControls                
:Using System.Web.UI.HtmlControls               

    ∇ Render output;HTML                        
      :Access public override                 
      :Signature Render  HtmlTextWriter output
      HTML←'<h3>Hello World</h3>'               
      output.WriteLine⊂HTML                     
    ∇                                           

:EndClass ⍝ SimpleCtl

The Render function supercedes (see :Access Statement) the Render method that SimpleCtl has inherited from its base class, System.Web.UI.Control.

The Render method defined by the System.Web.UI.Control base class is void and takes a parameter of type HtmlTextWriter. When the SimpleCtl control is referenced in a Web Page, ASP.NET creates an instance of it and calls its Render method because it is a Control and is expected to have one. Moreover, ASP.NET supplies an object of type HtmlTextWriter as its parameter. You do not need to worry where this object came from, or what it actually represents. You need only know that an HtmlTextWriter provides a method called WriteLine that may be used to output a text string to the browser. The mechanics of how this actually happens are handled by the HtmlTextWriter object itself.

In APL terms, the argument to our Render function, output, will be a namespace reference, and the function can simply call its WriteLine method with a character vector argument. This argument can contain any valid HTML string and defines the appearance of the SimpleCtl control.

Using the :Signature statement, the Render function is defined to have the same syntax as the method it overrides, that is, it does not return a result void and takes a single parameter of type HtmlTextWriter. Note that to successfully replace the base class method, the Render function must have exactly this :Signature.

Using SimpleCtl

Our SimpleCtl control may now be included in any .NET Web Page from which temp.dll is accessible. The file samples\asp.net\temp\Simple.aspx is simply an example. The fact that this control is written in Dyalog is immaterial. 

<%@ Register TagPrefix="Dyalog"
             Namespace="DyalogSamples" Assembly="temp" %>

<html>
<body>
<Dyalog:SimpleCtl runat=server/>
</body>
</html>

The first line of the script specifies that any controls referenced later in the script that are prefixed by Dyalog:, refer to custom controls in the .NET Namespace called DyalogSamples which is located in the Assembly temp.dll in the bin subdirectory.

simplectl3
Figure 1: simplectl3