Virtual Keyword in C#
- When a derived class want to override the base class member(s) then base class member(s) need to marked as virtual members.
- A function marked as virtual can be overridden by subclasses wishing to provide a specialized implementation.
- Methods, properties, indexers, and events can all be declared as virtual.
- In the derived class those members will be marked by override keyword.
Following example will illustrates briefly the concept of virtual keyword.
Creating Types
public class Asset
{
public string Name;
public virtual decimal Liability
{
get
{
return 0;
}
}
}
A subclass overrides a virtual method by applying the override modifier:
public class Stock : Asset
{
public long SharesOwned;
}
public class House : Asset
{
public decimal Mortgage;
public override decimal Liability
{
get
{
return Mortgage;
}
}
}
By default, the Liability of an Asset is 0. A Stock does not need to specialize this behavior. However, the House specializes the Liability property to return the value of the Mortgage:
House mansion = new House { Name="McMansion",Mortgage=250000 };
Console.WriteLine (mansion.Liability); // 250000
- The signatures, return types, and accessibility of the virtual and overridden methods must be identical.
- An overridden method can call its base class implementation via the base keyword.
