Of course, if we are going to have HTML elements that execute on the server, why not extend the concept even more? ASP+ changes each page into a server-side object, and exposes more properties, methods and events that can be used within your code to create the content dynamically. Each page becomes a tree of COM+ objects that can be accessed and programmed individually as required.
Using Server-side Control Events
To see how we can take advantage of this to structure our pages more elegantly, take a look at the following code. It shows the ASP+ page we used in our previous example, but with a couple of changes. This version of the page is named pagetwo.aspx:
<html>
<body>
<script language="VB" runat="server">
Sub ShowValues(Sender As Object, Args As EventArgs)
divResult.innerText = "You selected '" _
& selOpSys.value & "' for machine '" _
& txtName.value & "'."
End Sub
</script>
<div id="divResult" runat="server"></div>
<form runat="server">
Machine Name:
<input type="text" id="txtName" runat="server">
<p />
Operating System:
<select id="selOpSys" size="1" runat="server">
<option>Windows 95</option>
<option>Windows 98</option>
<option>Windows NT4</option>
<option>Windows 2000</option>
</select>
<p />
<input type="submit" value="Submit"
runat="server" onserverclick="ShowValues">
</form>
</body>
</html>
Firstly, notice that we've replaced the inline ASP+ code with a <script> section that specifies VB as the language, and includes the runat="server" attribute. Inside it, we've written a Visual Basic function named ShowValues. In ASP+, functions and subroutines must be placed inside a server-side <script> element, and not in the usual <%...%> script delimiters – we'll look at this in more detail in the next chapter.
We've also added an HTML <div> element to the page, including the runat="server" attribute. So this element will be created on the server, and is therefore available to code running there. When the VB subroutine is executed, it sets the innerText property of this <div> element.
Notice also how it gets at the values required (e.g. those submitted by the user). Because the text box and <select> list also run on the server, our code can extract the values directly by accessing the value properties of these controls. When the page is executed and rendered on the client, the <div> element that is created looks like this:
<div id="divResult">You selected 'Windows NT4' for
machine 'lewis'.</div>
Connecting Server-side Control Events To Your Code
By now you should be asking how the VB subroutine actually gets executed. Easy – in the <input> element that creates the Submit button, we added two new attributes:
<input type="submit" value="Submit"
runat="server" onserverclick="ShowValues">
The runat="server" attribute converts the HTML element into a server-side control that is 'visible' and therefore programmable within ASP+ on the server. The onserverclick="ShowValues" attribute then tells the runtime that it should execute the ShowValues subroutine when the button is clicked. Notice that the server-side event names for HTML controls include the word "server" to differentiate them from the client-side equivalents (i.e. onclick, which causes a client-side event hander to be invoked).
|
The result is a page that works just the same as the previous example, but the ASP+ source now has a much more structured and 'clean' format. It makes the code more readable, and still provides the same result – without any client-side script or other special support from the browser. If you view the source code in the browser, you'll see that it's just the same: |
|
This page, named pagetwo.asp, is in the Chapter01 directory of the samples available for the book. You can download all the sample files from our Web site at http://www.wrox.com.
You'll see how we can improve the structure even more, by separating out the code altogether, in Chapter 2. And, even better (as with earlier versions of ASP) we can add our own custom components to a page or take advantage of a range of server-side components that are provided with the NGWS framework.
Many of these can be tailored to create output specific to the client type, and controlled by the contents of a template within the page.
Comments