In this article I'm going to explain Delegate Covariance and Contravariance. I will try to make this article as simple as possible as this topic has been a source of confusion to some of the developers. To start with a plain definition of a delegate, A delegate is nothing but a list of one or more methods that can be called when required. A delegate can add to it only the methods that match its signature. A delegate is internally treated as a class. This article assumes that you have a basic knowledge of delegates. A basic knowledge of how a delegate is created and how the methods are added to the delegate and how are they invoked is required.

parseInt() is one of the common JavaScript methods which helps the developer to convert a string representation of a number into an integer. This method returns NaN when a valid number is not sent to it. The main intention of this article is to focus on a small situation where you will end up in receiving an incorrect number after you use parseInt method.

In this article I am going to demonstrate on how to make a hierarchical GridView which enables the user to open up the hierarchy with the click on a row, which enables the user to close the currently opened hierarchy when the user clicks on another row or the same row. Unlike the hierarchical grids which place a Plus or Minus sign to open and close the hierarchy, we will create this GridView without using them (i.e., the user will be able to just click the row and open up the hierarchy).

There are many posts in the forums where people ask how to make a Grid which behaves like an excel sheet i.e. a Grid which has resizable columns, a Grid which has resizable rows, a Grid which has editable cells, a Grid whose cells can be navigated by using the arrow keys and the Tab key, a focussed cell in the Grid which responds to the key strokes when a user starts typing. When you Google for an “Excel Like GridView” or “Excel Like DataGrid” what you get is a link which doesn’t meet your expectations or a link which is already dead. I hope you will enjoy this article on making “An Excel Like GridView.” I would like thank Matt Berseth whose blog provoked my thought on making “An Excel Like GridView.”