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Indexers In C#





  1. Introduction.
  2. Syntax.
  3. Creation of XML file.
  4. Creating a class to implement 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 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 list of subjects in div tag.
  4. A method GetListOfSubjects() is created. The purpose of this method is to get 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 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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