new Modifier (C# Reference)

When used as a modifier, the new keyword explicitly hides a member that's inherited from a base class. When you hide an inherited member, the derived version of the member replaces the base-class version. You can hide members without using the new modifier, but the result is a warning. If you use new to explicitly hide a member, the modifier suppresses this warning and documents the fact that the derived version is intended as a replacement.

To hide an inherited member, declare it in the derived class by using the same name, and modify it with the new modifier. For example:

public class BaseC
{
    public int x;
    public void Invoke() { }
}
public class DerivedC : BaseC
{
    new public void Invoke() { }
}

In this example, BaseC.Invoke is hidden by DerivedC.Invoke. The field x is not affected because it is not hidden by a similar name.

Name hiding through inheritance takes one of the following forms:

  • A constant, field, property, or type introduced in a class or struct hides all base class members with the same name.

  • A method introduced in a class or struct hides properties, fields, and types, with the same name, in the base class. It also hides all base class methods with the same signature.

  • An indexer introduced in a class or struct hides all base class indexers with the same signature.

It is an error to use both new and override on the same member because the two modifiers have mutually exclusive meanings. The new modifier creates a new member with the same name and causes the original member to become hidden. The override modifier extends the implementation for an inherited member. For examples that demonstrate the difference, see Knowing When to Use Override and New Keywords (C# Programming Guide).

Using the new modifier in a declaration that does not hide an inherited member generates a warning.

In this example, a base class, BaseC, and a derived class, DerivedC, use the same field name x, which hides the value of the inherited field. The example demonstrates the use of the new modifier. It also demonstrates how to access the hidden members of the base class by using their fully qualified names.

public class BaseC
{
    public static int x = 55;
    public static int y = 22;
}

public class DerivedC : BaseC
{
    // Hide field 'x'. 
    new public static int x = 100;

    static void Main()
    {
        // Display the new value of x:
        Console.WriteLine(x);

        // Display the hidden value of x:
        Console.WriteLine(BaseC.x);

        // Display the unhidden member y:
        Console.WriteLine(y);
    }
}
/*
Output:
100
55
22
*/

In this example, a nested class hides a class that has the same name in the base class. The example demonstrates how to use the new modifier to eliminate the warning message and how to access the hidden class members by using their fully qualified names.

public class BaseC 
{
    public class NestedC 
    {
        public int x = 200;
        public int y;
    }
}

public class DerivedC : BaseC 
{
    // Nested type hiding the base type members. 
    new public class NestedC   
    {
        public int x = 100;
        public int y; 
        public int z;
    }

    static void Main() 
    {
        // Creating an object from the overlapping class:
        NestedC c1  = new NestedC();

        // Creating an object from the hidden class:
        BaseC.NestedC c2 = new BaseC.NestedC();

        Console.WriteLine(c1.x);
        Console.WriteLine(c2.x);   
    }
}
/*
Output:
100
200
*/

If you remove the new modifier, the program will still compile and run, but you will get the following warning:

The keyword new is required on 'MyDerivedC.x' because it hides inherited member 'MyBaseC.x'.

For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.

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