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Workspace Behind

Code-Behind discusses how APL logic can be separated from page layout by placing it in a separate APL Source file which is referred to from the .aspx web page. It is also possible to have the code reside in a separate workspace. This allows you to develop web pages using a traditional workspace approach, and it is probably the quickest way to give an HTML front-end to an existing Dyalog application.

Code-Behind also shows that the fruit.apl file defined a new class called FruitSelection that inherits from System.Web.UI.Page. This class contains a Page_Load function that (by virtue of its name) overrides the Page_Load method of the underlying base class and will be called every time the web page is loaded or posted back. The Page_Load function takes whatever action is required, for example, initialisation. The class also contains a callback function to perform an action when a user presses a button.

A similar technique is employed when the code behind the web page is implemented in a separate workspace. The workspace should contain a class that inherits from System.Web.UI.Page. This class can contain a Page_Load function that will be invoked every time the corresponding web page is loaded and as many callback functions as are required to provide the application logic. The workspace is connected to one or more web pages by the Inherits="<classname>" and  src="<workspace>" declarations in the page directive statement that appears at the beginning of the web page script. The [DYALOG]\Samples\asp.net\actfns directory contains some examples of Dyalog systems that have been converted to run as web applications using this technique. Dyalog Ltd is grateful to David Hughes, who provided the original workspaces and advised on their conversion.

The two workspaces are called actfns.dws and proj.dws. The original code used the Dyalog GUI to display an input form, collect and validate the user's input, and calculate and display the results. The original logic supported field level validation, and results were immediately recalculated whenever any field was changed. With some exceptions, this has been changed so that the user must press a button to tell the system to recalculate the results. This approach is more appropriate in an Internet application, especially when connection speed is low. Apart from this change, the applications run approximately as originally designed.

Structure of the web application
Figure 1: Structure of the web application

Figure 1 illustrates the structure of the web application and the various files involved. The starting page, actfns.htm, provides a menu of options that link to various .aspx web pages. These pages are linked to one of the two workspaces through the src="" declaration.

The actfns.htm start page offers three application choices:

actfns.htm start page showing the three options
Figure 2: actfns.htm start page showing the three options

When the first option is selected, the system loads sla_tab.aspx. This defines the screen layout in terms of ASP.NET controls, including the DataGrid control for tabulating the results. sla_tab.aspx contains the declaration Inherits="actuarial" src="actfns.dws", so ASP.NET loads the actuarial class from this workspace (using a call to Dyalog). When the page is loaded, it generates a Page_Load event, which calls its Page_Load method. This populates the ASP controls with data; the resulting web page is shown in Figure 3.

The page displayed when <strong>Tabulate single life insurance and annuity values</strong> is selected
Figure 3: The page displayed when Tabulate single life insurance and annuity values is selected

The mechanisms involved are described in Converting an Existing Workspace.