Published: Sunday, February 25, 2001
4GuysFromRolla.com - Using Object-Orientation in ASP.NET: Polymorphism, Part 2
By Ian Stallings
Read Part 1
In Part 1 we introduced the concept of polymorphism
and looked at creating an ISaveData interface and having our Profile
class inherit from this interface. Once Profile inherited from this interface,
it could implement its own version of the .save() method. Since
ExtendedProfile inherits from our Profile class,
ExtendedProfile can also implement its own version of the .save()
method. In this part we'll look at ExtendedProfile's implementation of this method
and how to call this method for both classes from an ASP.NET page!
Since the interface was implemented by ExtendedProfile's superclass,
Profile, the IsaveData interface and it's method
.save() is inherited. In this ExtendedProfile class I decided
that I wanted to save the data into an XML file. I can share this XML file with other
applications allowing them to access file. Later I can recreate the state of the object by
reading the values from this file.
public override void save()
{
String _document =
"c:\\inetpub\\wwwroot\\asp.net\\polymorphism\\newbooks.xml";
XmlTextWriter writer = null;
try
{
writer = new XmlTextWriter (_document, null);
writer.Formatting = Formatting.Indented;
writer.WriteStartDocument(false);
writer.WriteDocType("Profile", null, null, null);
writer.WriteStartElement("Profile");
writer.WriteElementString("firstName", _firstName);
writer.WriteElementString("lastName", _lastName);
writer.WriteElementString("phoneNumber", _phoneNumber);
writer.WriteElementString("address1", _address1);
writer.WriteElementString("address2", _address2);
writer.WriteElementString("city", _city);
writer.WriteElementString("state", _state);
writer.WriteElementString("postal", _postal);
writer.WriteEndElement();
writer.Flush();
writer.Close();
}
catch(Exception e)
{
Console.WriteLine ("Exception: {0}", e.ToString());
}
}
|
So above we have a situation where we used the same method name with different implementations
using polymorphism. We can access these classes and test them using the following ASP.NET
(.aspx) code:
<%@ Import Namespace="Shai" %>
<html>
<style>
div
{
font: 8pt verdana;
background-color:cccccc;
border-color:black;
border-width:1;
border-style:solid;
padding:10,10,10,10;
}
</style>
<script language="C#" runat="server">
public void Page_Load(Object sender, EventArgs E) {
/*
We create an instance of the superclass
below and save the data in binary format:
*/
Profile profile = new Profile();
Message.InnerHtml += "<u>Profile Class</u><br>" +
"First: " + profile.getFirstName() + "<br>" +
"Last: " + profile.getLastName() + "<br>" +
"Phone: " + profile.getPhoneNumber() + "<br><br>";
profile.save();
/*
Then we create an instance of the subclass below
and save the data in xml format:
*/
ExtendedProfile extendedProfile = new ExtendedProfile();
Message.InnerHtml += "<u>ExtendedProfile Class</u><br>" +
"First: " + profile.getFirstName() + "<br>" +
"Last: " + profile.getLastName() + "<br>" +
"Phone: " + extendedProfile.getPhoneNumber() + "<br>" +
"Adress1: " + extendedProfile.getAdress1() + "<br>" +
"Adress2: " + extendedProfile.getAdress2() + "<br>" +
"City: " + extendedProfile.getCity() + "<br>" +
"State: " + extendedProfile.getState() + "<br>" +
"Postal: " + extendedProfile.getPostal() + "<br>" +
"Description: " + extendedProfile.getDescription()+"<br>";
extendedProfile.save();
}
</script>
<body style="font: 10pt verdana">
<b><h3>Simple Inheritance/Polymorphism Example</h3></b>
<br><br>
Object Output:<br><br>
<div id="Message" runat="server"/>
</body>
</html>
|
And there you have it! This sample above will call both methods. One creating a
.bin file, the other creating an .xml file. I have attached a
zip file that contains the this article, the source code for the sample, the compiled dll,
and instructions on how to compile and use the samples. You must have the .Net Framework
SDK Beta1 installed on the machine in order to compile the samples and run them correctly. But
even if you don't have the SDK installed (download the Beta1 SDK
for free from www.ASP.NET) you can take a look at the sample source files
and see polymorphism, OOP, and see how using .Net to build applications can make your life
a little easier.
Happy Programming!
By Ian Stallings
Attachments:
Download the source code (in ZIP format)
Visit the ASP.NET Article Index
Read Ian's Other ASP.NET OOP Articles
