OptionalAttribute Class

Definition

Indicates that a parameter is optional.

public ref class OptionalAttribute sealed : Attribute
[System.AttributeUsage(System.AttributeTargets.Parameter, Inherited=false)]
public sealed class OptionalAttribute : Attribute
[System.AttributeUsage(System.AttributeTargets.Parameter, Inherited=false)]
[System.Runtime.InteropServices.ComVisible(true)]
public sealed class OptionalAttribute : Attribute
[<System.AttributeUsage(System.AttributeTargets.Parameter, Inherited=false)>]
type OptionalAttribute = class
    inherit Attribute
[<System.AttributeUsage(System.AttributeTargets.Parameter, Inherited=false)>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type OptionalAttribute = class
    inherit Attribute
Public NotInheritable Class OptionalAttribute
Inherits Attribute
Inheritance
OptionalAttribute
Attributes

Examples

The following code example demonstrates how to apply the OptionalAttribute attribute to a parameter of a method written in C#.

using System;
using System.Runtime.InteropServices;

public class Program
{
    public static void MethodWithOptionalAttribute([Optional] string str)
    {
        Console.WriteLine($"str is null: {str == null}");
    }

    public static void Main()
    {
        MethodWithOptionalAttribute(); // str is null: True
        MethodWithOptionalAttribute("abc"); // str is null: False
    }
}

Remarks

You can apply this attribute to parameters.

Optional parameters are not supported by all languages.

OptionalAttribute is sometimes used in conjunction with DefaultParameterValueAttribute.

Constructors

OptionalAttribute()

Initializes a new instance of the OptionalAttribute class with default values.

Properties

TypeId

When implemented in a derived class, gets a unique identifier for this Attribute.

(Inherited from Attribute)

Methods

Equals(Object)

Returns a value that indicates whether this instance is equal to a specified object.

(Inherited from Attribute)
GetHashCode()

Returns the hash code for this instance.

(Inherited from Attribute)
GetType()

Gets the Type of the current instance.

(Inherited from Object)
IsDefaultAttribute()

When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.

(Inherited from Attribute)
Match(Object)

When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.

(Inherited from Attribute)
MemberwiseClone()

Creates a shallow copy of the current Object.

(Inherited from Object)
ToString()

Returns a string that represents the current object.

(Inherited from Object)

Explicit Interface Implementations

_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.

(Inherited from Attribute)
_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.

(Inherited from Attribute)
_Attribute.GetTypeInfoCount(UInt32)

Retrieves the number of type information interfaces that an object provides (either 0 or 1).

(Inherited from Attribute)
_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.

(Inherited from Attribute)

Applies to