Events in C# .Net:

[sukishan]

Events in C# .Net:

Delegate usefulness does not just lie in the fact that it can hold the references to functions but in the fact that it can define and use function names at runtime and not  at compile time. A large goal of design delegates is their applicability in events model of .Net. Events are the actions of the system on user manipulations (e.g. mouse clicks, key press, timer etc.) or any event triggered by the program. To understand the usage of delegates for event model, the previous examples are used here. We should add to our Figure class next things:

public delegate void FigureHandler(string msg);
public static event FigureHandler Inverted; 
public void InvertZ()
{

   m_zPos = - m_zPos;
   Inverted("inverted by z-axis");

}


   Now we have a delegate declared and event that uses this delegate's type. In every function we should call our event. The next code snippet should explain it clearly:

static void Main(string[] args)
{ 
   Figure figure = new Figure(10,20,30);
   Figure.Inverted+=new Test.Figure.FigureHandler(OnFigureInverted);
   figure.InvertX();
   figure.InvertZ();
}
private static void OnFigureInverted(string msg)
{
  Console.WriteLine("Figure was {0}",msg);
}


   So, in the main function we should create an object of figure class and attach event handler to the method OnFigureInverted. And when we call any of invert methods the event is fired and it calls our event handler. The application will print the following string into the console: Figure was inverted by x-axis Figure was inverted by z-axis There was simple examples of using delegates and events and should be treated as a starting point to learn it more yourself. Download the C# Delegates source files from the link. To compile and run it need to run .NET command line. Just type: csc TestClass.cs. It creates TestClass.exe that can be run as standard executable file.