Jim Fawcett CSE791 – Distributed Objects Spring 2001 COM and the Web Jim Fawcett CSE791 – Distributed Objects Spring 2001

Web Programming Model Web Programming supports distributed processing: Client-side: XHTML, scripts, ActiveX controls, Java Applets Server-side: CGI (C,C++,Perl,…), ASP (Vbscript, JavaScript), ISAPI (C, C++)

Programming Models Both browser and web-server support a programming model: Browser – window/document/element Web Server – Request & Response objects In IE5 and IIS the programming model is derived from a parse tree: IE5 builds parse tree from XHTML elements. IIS builds parse tree from ASP pages and server-side scripts.

Powerful Programming Model This is a very flexible, powerful model: Can plug in reusable control components Support methods, properties, events Applications can support the browser and DHTML parser controls: So both the application and the web page can determine what the user sees and how a user interacts with the system by interacting with the DHTML parse tree.

What does Control have to Provide? To be hosted in a web page and communi-cate through events, the web page must: Provide dispatch interfaces Provide connectable objects for each event type Implement IProvideClassInfo2 Implement IObjectSafety Provide property persistance Uses (parts of) structured storage All of these are supported with Impl classes in ATL

What does Web Page have to Provide? Object tag with control GUID A script-based event handler Script-based calls to control’s methods Param tags to set properties Very little work for Web Page designer. A lot of work for the control designer.

DHTML Behaviors The Browser model has been strengthened in IE5.5 by supporting behaviors: A style-based subroutine that determines how a specific tag will behave.

Programming Model Again This web programming model allows us to do some very interesting things: We can build GUIs that the user can change easily, in some fundamental ways, if we base it on the web model, e.g.: An application that provides basic resources. Controls that provide reusable blocks of behavior Controls can simply provide intricate behavior They can also bind to data sources, e.g., xml or relational databases. A web page that binds to controls, sets styles and behaviors, and provides most of the content. The user can control the GUI by modifying DHTML