Page 218 - DCAP408_WEB_PROGRAMMING

Web Programming

Notes In Figure 8.3, the first stage deals with Web control initialization. We don’t need to be too
concerned about this stage in our own programming tasks.
Our code is frequently involved in the second stage of Web forms processing, when the ASP.NET
infrastructure fires the Load event in the Page class. As Listing 1 shows, we can use the Page_Load
event (Lines 20-30) to change the contents of controls or to perform any other kinds of processing
before a page is rendered. If the page posts back to itself (that is, if the user clicks the Convert
button), the Page_Load event will fill in zeros if the user leaves any field blank (Lines 22-27).

The third stage of Web forms processing is for control event handling, which happens only if the
user manipulates one of the Web controls on the page. This stage won’t happen if this is the first
time the user is browsing this particular page. In above Listing, the On Convert method is called
during this stage (Lines 32-38). Note that event handling happens after the Page_Load event. In
the fourth stage, the HTML for the page is rendered. This process involves calling the Render
method for the page, which will call the Render method for every control, among other things.

Notes Listing 1 doesn’t contain an explicit Render method because the page class and Web
control classes have default implementations for it already. We will need to override the
Render method only if we want to customize the exact HTML that each class produces.
In the last stage, the Page_Unload event for every gets called. We can use the Unload event
to clean up database connections and other objects that have to be closed explicitly, for
example. (Listing 1 also doesn’t define the Page_Unload event because it doesn’t need to
clean up any objects.)

Self Assessment

Fill in the blanks:
13. A …………………… is another name for an ASP.NET page.

14. A Web form may be processed after the user interacts with one of the ……………………
controls.
15. A Web form is rendered when the user initially browses to the …………………… file.

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