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Indexers In C#





  1. Introduction
  2. Syntax
  3. Creation of XML file
  4. Creating a class to implement an indexer
  5. Code explanation
  6. Reading the XML file
  7. Conclusion

Introduction







Syntax


<modifier> <return type > this[argument list] {
	get {
		// Get codes goes here
	}
	set {
		// Set codes goes here
	}
}




Creation Of XML File




<root>
    <subject value = ".Net"></subject>
    <subject value = ".Net Web Service"></subject>
    <subject value = "ADO.NET"></subject>
    <subject value = "IBM Lotus Notes"></subject>
    <subject value = "JavaScript"></subject>
    <subject value = "Silverlight"></subject>
    <subject value = "Software Testing"></subject>
    <subject value = "SQL Server"></subject>
    <subject value = "WPF"></subject>
</root>





Creating A Class To Implement An Indexer


class Subject
{
    private Dictionary<string, string> _subjectDictionary = new Dictionary<string, string>();

    /// <summary>
    /// Indexer
    /// </summary>
    /// <param name="index"></param>
    /// <returns></returns>
    public string this[int index]
    {
        get
        {
            string key = _subjectDictionary.Keys.Where((n, i) => i == index).FirstOrDefault();
            return string.Format("{0}", _subjectDictionary[key]);
        }
    }

    /// <summary>
    /// Get List of subjects
    /// </summary>
    private void GetListOfSubjects()
    {
        DataSet ds = new DataSet();
        ds.ReadXml("subject.xml");
        for (int i = 0; i < ds.Tables[0].Rows.Count - 1; i++)
        {
            _subjectDictionary.Add(i.ToString(), ds.Tables[0].Rows[i]["value"].ToString());
        }
    }

    /// <summary>
    /// Constructor
    /// </summary>
    public Subject()
    {
        if (_subjectDictionary.Count == 0)
        {
            GetListOfSubjects();
        }
    }
    /// <summary>
    /// Subject Count to save from 
    /// index out of range
    /// </summary>
    public int SubjectCount
    {
        get
        {
            return _subjectDictionary.Count;
        }
    }
}




Code Explanation




  1. First of all an object of type dictionary is created
  2. private Dictionary<string,string> _subjectDictionary = new Dictionary<string,string>();



  3. A property "SubjectCount" is created to get the count of items in "_subjectDictionary". This property is optional but it is better to create it, because when you loop through "_subjectDictionary", then this property ensures that you won’t get any index out-of-range run time error. I will come back to this point when I will show the list of subjects in the "div" tag
  4. A method "GetListOfSubjects()" is created. The purpose of this method is to get a list of subjects from XML (It should be noted that I have ignored the validation part deliberately to make the code simple and easy to understand)
  5. A constructor to call the "GetListOfSubjects()" method
  6. Indexer is defined
public string this[int index] {
	get {
		string key = _subjectDictionary.Keys.Where((n, i) = >i == index).FirstOrDefault();
		return string.Format("{0}", _subjectDictionary[key]);
	}
}






Reading The Xml File




Subject oSubject = new Subject();
StringBuilder sbMenu = new StringBuilder(string.Empty);
sbMenu.Append("<ul id = \"MenuLeft\">");
for (int i = 0; i < oSubject.SubjectCount; i++) {
	sbMenu.Append("<li>");
	sbMenu.Append(oSubject[i].ToString());
	sbMenu.Append("</li>");
}
sbMenu.Append("</ul>");
divLeftMenu.InnerHtml = sbMenu.ToString();






Conclusion





Posted By  -  Karan Gupta
 
Posted On  -  Monday, June 21, 2010

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