Retrieving and Processing XML with ASP.Net - Using the XML Exchanger

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To provide the most basic of examples on which you can feel free to expand to your heart’s content, let’s assume our client application is simply looking to retrieve information about a person. For this person, we have only the user ID, and we know we can query our remote user database through a web API, that will return all the details in XML format. I’ll step through the code, just as I did with the XMLExchanger class.

namespace MyXMLProject
{
  // step 1
  using System;
  using System.Web.UI;
  using System.Web.UI.HtmlControls;
  using System.Web.UI.WebControls;
  using System.Xml;

  public class WebForm1 : Page
  {

    // step 2
    protected TextBox EmailTxt;
    protected TextBox FirstNameTxt;
    protected TextBox LastNameTxt;
    protected TextBox CompanyTxt;

    private void Page_Load(object sender, EventArgs e)
    {

      if (!IsPostBack)
      {

        // step 3
        int userID;
        try
        {
          userID = Convert.ToInt16(Request.QueryString["id"]);
        }
        catch (Exception)
        {
          userID = 0;
        }

        // step 4
        LoadDataFromXML(GetXML(userID));
      }
    }

    private XmlTextReader GetXML(int userID)
    {
      // step 5
      XMLExchanger exchange1 = new XMLExchanger();
      exchange1.proxy =
        (Request.ServerVariables["SERVER_NAME"].IndexOf("localhost") == -1)
         ? "http://liveproxy:8080" : "http://testproxy";

      // step 6
      XmlTextReader reader1 = null;
      try
      {
        reader1 = exchange1. transmitXML("?userID=" + userID);
      }
      catch (Exception exception1)
      {
        // however you want to surface the error
      }
      return reader1;
    }

    // step 7
    private void LoadDataFromXML(XmlTextReader xtr)
    {
      while (xtr.Read())
      {
        string text2;
        // step 8
        if (xtr.NodeType != XmlNodeType.Element)
        {
          continue;
        }
        string text1 = xtr.Name.ToLower();
        xtr.Read();
        if (xtr.NodeType == XmlNodeType.Text)
        {
          text2 = xtr.ReadString();
          switch (text1)
          {
            case "email":
            {
              this.EmailTxt.Text = text2;
              continue;
            }
            case "firstname":
            {
              this.FirstNameTxt.Text = text2;
              continue;
            }
            case "lastname":
            {
              this.LastNameTxt.Text = text2;
              continue;
             }
             case "company":
             {
               this.CompanyTxt.Text = text2;
               continue;
            }
          }
        }
      }
    }
  }
}

Code Explained

Steps:

1. Import the namespaces, don’t forget System.Xml!
2. Declare objects on the ASP.Net page in this case. This will be unnecessary with .Net 2.0 and the advent of partial classes. I’m only reading first and last name, email, and company. You can customize this to your needs.
3. Here we attempt to pull the user ID out of the query string. If it is not a valid integer value, then you can decide how you want to display an error. For the sake of simplity, I just assigned the value of 0 to move on with the code. You would however opt to prompt the user to input a valid user ID.
4. Here two steps actually take place on one line. First we call the GetXML method with the ID of the user, which in turn uses our XMLExchanger class. This returns XML, which we pass into the method to load the data into our form fields.
5. Here’s where we’re actually instantiating the XMLExchanger class, and declaring its properties. There’s a nice line there to switch the proxy depending if you’re running the code in development versus production, therefore you wouldn’t need to manually change the proxy before deploying the application.
6. Here we call the transmitXML method, passing only the string necessary to get the user info. Therefore the default URL is being used, only the query string parameter is appended. You could even pass through XML in string format here, if that’s what your remote system requires to process a request. An XML reader is returned.
7. This method steps through the XML, node by node to read the data, and populate the appropriate fields with the pertinent user information. I use ‘while xtr.Read()’ to sequentially read the XML until the end.
8. Depending on how the data is structured, you may need to modify this to suit your needs. I wanted to read only elements, so I skip everything else. You can set it up to look for attributes, or anything else you need to read.

XML is a very fast, reliable method of transmitting data. No doubt the methods described in this article will be useful to you, they’ve proven themselves essential in a number of applications I’ve created.

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