What do you mean by Override?

Question

1.What do you mean by Override?What's the use of it? Any simple example/Article? 2. What's the meaning of keywords in the following: protected override void OnMouseMove(MouseEventArgs e)

alobiuc · Answer

Oh, I forgot to mention: -aside methods, also properties and indexers can be overriden; -the base method can (must) be marked as virtual or as abstract; -the signature of the overriden property must match exactly the base property. For more info, take a look here: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csref/html/vclrfoverridepg.asp

alobiuc · Answer

1. To override a method means to implement a different behaviour of it than the original one. For example, if you have a base class which implements a certain method and you want it to behave differently in a derived class, you override it in the derived class. In order for a method to be overriden, it must be marked as virtual in the base class: class BaseClass { public BaseClass(){} public virtual void method1(int x) {Console.Writeline("X is: {0}",x);} } class DerivedClass: BaseClass { public DerivedClass(){} public override void method1(int x) {Console.Writeline("X+1 is {0}",(x+1));} } class MainClass {public MainClass(){} BaseClass b=new BaseClass(); DerivedClass d=new DerivedClass(); b.method1(10);//output: "X is 10" d.method1(10);//output: "X+1 is 11"; } If you hadn't overriden the method1 in DerivedClass and you would call: d.method1(10) the output would be: "X is 10". 2. protected -- the access level for the method override -- as described at (1) void -- return type MouseEventArgs e -- this is not a keyword but a parameter of type MouseEventArgs, a class that holds informations about a MouseEvent. Also, this is a class derived from the Event class.