Using XML in C# in the simplest way

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Introduction

Like HTML, XML is made for the World Wide Web but the set of tags are not fixed. They can be extended and hence the name. We can have our own tags. The only thing we have to do is to maintain a structural relationship between them. It's written in SGML (Standard Generalized Markup Language) which is an international standard for defining descriptions across the globe.

XML was developed way back in 1996 by an XML Working Group (known originally as the SGML Editorial Review Board) which was formed under the guidance of the World Wide Web Consortium (W3C) which was chaired by Jon Bosak of Sun Microsystems. But, B-U-T, but many of us in spite of being in IT, still do not know much about XML. Like my previous article, even this one assumes the reader to be a beginner (or intermediate) to help you know even some hidden facts.

Getting late!! Let's get back to work first!!

To start with, just follow the instructions step by step. Thanks in advance for your co-operation. :)

Step By Step Walkthrough

1. Goto File->New->Blank Solution.
2. Select Visual C# Projects in Project Types.
3. Select WindowsApplication in Templates.
4. Type for eg., XMLReadWrite in the Name textbox.

Creating an XML file (the data file which will be read by our application)

Note: You will be demonstrated in Visual Studio .NET but you can create an XML file in literally any text editor.

1. Go to menu Project->Add New Item.
2. In the dialog box select XMLFile and click Open.

   Note:- It is generally recommended to give an appropriate name wherever required but please follow the instructions as it is, for simplicity.

3. Locate the following line.

   <?xml version="1.0" encoding="utf-8" ?> 

4. Below the line, add the following XML piece.

   <Book>
       <BookName>C# Professional</BookName>
       <BookName>C# Cookbook</BookName>
       <BookName>SQL Server Black Book</BookName>
       <BookName>Mastering VB.Net</BookName>
       <BookName>ASP.Net Unleashed</BookName>
       <BookName>.Net Framework Essentials</BookName>
       <ReleaseYear>2001</ReleaseYear>
       <ReleaseYear>2002</ReleaseYear>
       <ReleaseYear>2003</ReleaseYear>
       <ReleaseYear>2004</ReleaseYear>
       <Publication>EEE</Publication>
       <Publication>Microsoft Press</Publication>
       <Publication>O 'Reilly</Publication>
       <Publication>BpB</Publication>
       <Publication>Sams TechMedia</Publication>
   </Book>

Creating the schema (.XSD) file for validating our just made .xml file)

1. Go to menu XML -> Create Schema.
2. Notice that in the solution explorer, it has created a file XMLFile1.xsd.
3. Also notice what the IDE (Integrated Development Environment) has added in <Book> tag of ours.
4. It signifies our .xml file will be validated against which Schema file.

Creating a class clsSValidator

1. In the solution explorer, right click the XMLReadWrite project name.
2. Go to Add-> New Folder and name the folder as Classes.
3. Now right click the Classes folder name in the solution explorer.
4. Go to Add-> Add New Item.
5. Select class and name it as clsSValidator.cls.
6. This class needs the following namespaces. So paste it on top of the class.

     using System;
     using System.Xml;
     using System.Xml.Schema; 
     using System.Windows.Forms;

7. Just above the constructor, declare the following variables:

   // variable declarations 
     private string m_sXMLFileName ;
     private string m_sSchemaFileName ;
     private XmlSchemaCollection m_objXmlSchemaCollection ;
     private bool m_bIsFailure=false ;

8. Below the constructor clsSValidator, paste the following:

   //We are overloading the constructor
   //The following code creates a XmlSchemaCollection object 
   //this objects takes the xml file's Schema and adds it to its collection
   public clsSValidator (string sXMLFileName, string sSchemaFileName)
   { 
      m_sXMLFileName = sXMLFileName; 
      m_sSchemaFileName = sSchemaFileName;
      m_objXmlSchemaCollection = new XmlSchemaCollection ();
      //adding the schema file to the newly created schema collection
      m_objXmlSchemaCollection.Add (null, m_sSchemaFileName); 
   }

9. Just below the above code, add the following function:

   //This function will Validate the XML file(.xml) against xml schema(.xsd)
   public bool ValidateXMLFile()
   {
     XmlTextReader objXmlTextReader =null;
     XmlValidatingReader objXmlValidatingReader=null ;
   
     try
     { 
       //creating a text reader for the XML file already picked by the 
       //overloaded constructor above viz..clsSchemaValidator
       objXmlTextReader = new XmlTextReader(m_sXMLFileName); 
       //creating a validating reader for that objXmlTextReader just created
       objXmlValidatingReader = new XmlValidatingReader (objXmlTextReader);
       //For validation we are adding the schema collection in 
       //ValidatingReaders Schema collection.
       objXmlValidatingReader.Schemas.Add (m_objXmlSchemaCollection);
       //Attaching the event handler now in case of failures
       objXmlValidatingReader.ValidationEventHandler += 
                      new ValidationEventHandler 
       (ValidationFailed);
       //Actually validating the data in the XML file with a empty while.
       //which would fire the event ValidationEventHandler and invoke 
       //our ValidationFailed function
       while (objXmlValidatingReader.Read())
       {
       }
       //Note:- If any issue is faced in the above while it will invoke 
       //ValidationFailed which will in turn set the module level 
       //m_bIsFailure boolean variable to false thus returning true as  
       //a signal to the calling function that the ValidateXMLFile
       //function(this function) has encountered failure
       return m_bIsFailure;
       }
     catch (Exception ex)
     {
       MessageBox.Show ("Exception : " + ex.Message);
       return true;
     }
     finally 
     {
       // close the readers, no matter what.
       objXmlValidatingReader.Close (); 
       objXmlTextReader.Close ();
     }
   }

10. Notice that we are using an event handler in the ValidateXML function above.
11. Add the following snippet right below it:

    private void ValidationFailed (object sender, ValidationEventArgs args)
    {
      m_bIsFailure = true;
      MessageBox.Show ("Invalid XML File: " + args.Message);
    } 
    //This will be called only if an the XML file is not in proper format.
    //Since it is a file like HTML any one can go and change its format from 
    //any text editor. So we shud ensure that we are validating it properly.

Reading the values from the XML file

1. Right click Form1 in Solution Explorer and select View Code.
2. Replace the namespaces used on the top by the following snippet:

   using System;
   using System.Windows.Forms;
   using System.Xml;
   using XMLReadWrite.Classes;

3. Right click Form1 in Solution Explorer and select View Designer.
4. From the toolbox, place three labels, three comboboxes and one command button as shown in the figure.
5. Change their properties as following:

   Name	Property	Value
   Label1	Caption	Book Name
   Label2	Caption	Release Year
   Label3	Caption	Publication
   Combo1	(Name)	cboBookName
   	Text	[make it blank]
   	DropDownStyle	DropDownList
   Combo2	(Name)	cboReleaseYear
   	Text	[make it blank]
   	DropDownStyle	DropDownList
   Combo3	(Name)	cboPublication
   	Text	[make it blank]
   	DropDownStyle	DropDownList
   Button1	(Name)	cmdWriteToFile
   	Text	&Write To File

6. Double click on the form (not on any other controls area) to open its Load event.

   Note: XmlTextReader (Namespace:- System.Xml) is used in our code below. It gives a read-only forward only access. This class helps us to read XML from stream or file with a very important feature of skipping unwanted data from it. Check out our usage below:

7. Just above the Load event paste the following code:

   private void ReadXMLFileAndFillCombos()
   {
     try
     {
       string sStartupPath = Application.StartupPath;
       clsSValidator objclsSValidator = 
             new clsSValidator(sStartupPath +  @"..\..\..\XMLFile1.xml", 
             sStartupPath +  @"..\..\..\XMLFile1.xsd");
       if (objclsSValidator.ValidateXMLFile()) return;
       XmlTextReader objXmlTextReader = 
             new XmlTextReader(sStartupPath +  @"..\..\..\XMLFile1.xml"); 
       string sName="";
       while ( objXmlTextReader.Read() ) 
       { 
         switch (objXmlTextReader.NodeType)
         {
           case XmlNodeType.Element:
           sName=objXmlTextReader.Name;
           break;
           case XmlNodeType.Text:
           switch(sName)
           {
             case "BookName":
             cboBookName.Items.Add(objXmlTextReader.Value); 
             break;
             case "ReleaseYear":
             cboReleaseYear.Items.Add(objXmlTextReader.Value); 
             break;
             case "Publication":
             cboPublication.Items.Add(objXmlTextReader.Value); 
             break;
           }
           break;
         }
       } 
     }
     catch(Exception ex)
     {
       MessageBox.Show(ex.ToString());
     }
   }

8. Now in the load event paste the following to call this method:

    ReadXMLFileAndFillCombos();

Writing the values to the XML file

1. Now right click the form1 again in solution explorer and go to its designer.
2. Double click the command button to see its Click event.

   Note: XmlTextWriter (Namespace: System.Xml) is used in our code below. This class helps us to write XML on many places like stream, console, file etc. We are pushing the XML on a file. Simply nest the Start and End method and it's done.

3. Just above the click event paste the following snippet:

   private void WriteXMLFileUsingValuesFromCombos()
   {
     try
     {
       string sStartupPath = Application.StartupPath;    
       XmlTextWriter objXmlTextWriter = 
            new XmlTextWriter(sStartupPath +  @"\selected.xml",null);
       objXmlTextWriter.Formatting = Formatting.Indented;
       objXmlTextWriter.WriteStartDocument();
       objXmlTextWriter.WriteStartElement("MySelectedValues");
       objXmlTextWriter.WriteStartElement("BookName");
       objXmlTextWriter.WriteString(cboBookName.Text);
       objXmlTextWriter.WriteEndElement();
       objXmlTextWriter.WriteStartElement("ReleaseYear");
       objXmlTextWriter.WriteString(cboReleaseYear.Text);
   
       objXmlTextWriter.WriteEndElement();
       objXmlTextWriter.WriteStartElement("Publication");
       objXmlTextWriter.WriteString(cboPublication.Text); 
       objXmlTextWriter.WriteEndElement();
       objXmlTextWriter.WriteEndElement();
       objXmlTextWriter.WriteEndDocument();
       objXmlTextWriter.Flush();
       objXmlTextWriter.Close();
       MessageBox.Show("The following file has been successfully created\r\n" 
           + sStartupPath 
           + @"\selected.xml","XML",MessageBoxButtons.OK,
           MessageBoxIcon.Information );
     }
     catch(Exception ex)
     {
       MessageBox.Show(ex.ToString());
     }
   }

4. Now we have to call this method from the click event of the button. So make it look like the following:

   private void cmdWriteToFile_Click(object sender, System.EventArgs e)
   {
     WriteXMLFileUsingValuesFromCombos();
   }

5. Run it to see its beauty ;)

Njoi programming!!

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