Question

Why wouldn’t I choose abstract? What are the limitations to declaring a class member virtual? Can only methods be declared virtual?

Answer 1

An abstract method or property (both can be virtual or abstract) can only be declared in an abstract class and cannot have a body, i.e. you can’t implement it in your abstract class.

A virtual method or property must have a body, i.e. you must provide an implementation (even if the body is empty).

If someone want to use your abstract class, he will have to implement a class that inherits from it and explicitly implement the abstract methods and properties but can chose to not override the virtual methods and properties.

Exemple :

using System; using C=System.Console;  namespace Foo {     public class Bar     {         public static void Main(string[] args)         {             myImplementationOfTest miot = new myImplementationOfTest();             miot.myVirtualMethod();             miot.myOtherVirtualMethod();             miot.myProperty = 42;             miot.myAbstractMethod();         }     }      public abstract class test     {         public abstract int myProperty         {             get;             set;         }          public abstract void myAbstractMethod();          public virtual void myVirtualMethod()         {             C.WriteLine('foo');         }          public virtual void myOtherVirtualMethod()         {         }     }      public class myImplementationOfTest : test     {         private int _foo;         public override int myProperty         {             get { return _foo; }             set { _foo = value; }         }          public override void myAbstractMethod()         {             C.WriteLine(myProperty);         }          public override void myOtherVirtualMethod()         {             C.WriteLine('bar');         }     } }