DefaultParameterValueAttribute 类

定义

设置当从支持默认参数的语言中调用参数时参数的默认值。Sets the default value of a parameter when called from a language that supports default parameters. 无法继承此类。This class cannot be inherited.

public ref class DefaultParameterValueAttribute sealed : Attribute
[System.AttributeUsage(System.AttributeTargets.Parameter)]
public sealed class DefaultParameterValueAttribute : Attribute
type DefaultParameterValueAttribute = class
    inherit Attribute
Public NotInheritable Class DefaultParameterValueAttribute
Inherits Attribute
继承
DefaultParameterValueAttribute
属性

示例

下面的代码示例演示如何将 DefaultParameterValueAttribute 特性应用于用编写的方法的参数C#。The following code example demonstrates how to apply the DefaultParameterValueAttribute attribute to a parameter of a method written in C#.

static public void MethodWithDefaultParam([System.Runtime.InteropServices.DefaultParameterValue("DEFAULT_PARAM_VALUE")] string var)
{
    Console.WriteLine("The passed value is: " + var);
}

注解

DefaultParameterValueAttribute 属性允许你使用不支持默认参数的语言指定默认参数值。The DefaultParameterValueAttribute attribute allows you to specify a default parameter value in a language that does not otherwise support default parameters. 将此特性应用于代码后,支持默认参数的语言可以使用指定的值作为默认参数。After you apply this attribute to your code, languages that support default parameters can use the specified value as a default parameter.

请注意,DefaultParameterValueAttribute 不会向不支持此功能的语言添加对默认参数的支持。Note that the DefaultParameterValueAttribute does not add support for default parameters to languages that do not support this feature. 例如,如果你将 DefaultParameterValueAttribute 与用编写的方法C#(不支持默认参数)结合使用,则在从C#调用方法时,不能使用默认参数。For example, if you use the DefaultParameterValueAttribute with a method written in C#, which does not support default parameters, you cannot use the default parameter when calling the method from C#. 仅当使用支持功能的语言(如) C++调用方法时,才可以使用默认参数。You can use the default parameter only when calling the method in a language such as C++ that does support the feature.

对于指定 COM 互操作接口的方法的默认参数,DefaultParameterValueAttribute 特别有用。The DefaultParameterValueAttribute is particularly useful to specify default parameters for methods of a COM interop interface.

构造函数

DefaultParameterValueAttribute(Object)

用参数的默认值初始化 DefaultParameterValueAttribute 类的新实例。Initializes a new instance of the DefaultParameterValueAttribute class with the default value of a parameter.

属性

TypeId

在派生类中实现时,获取此 Attribute 的唯一标识符。When implemented in a derived class, gets a unique identifier for this Attribute.

(继承自 Attribute)
Value

获取参数的默认值。Gets the default value of a parameter.

方法

Equals(Object)

返回一个值,该值指示此实例是否与指定的对象相等。Returns a value that indicates whether this instance is equal to a specified object.

(继承自 Attribute)
GetHashCode()

返回此实例的哈希代码。Returns the hash code for this instance.

(继承自 Attribute)
GetType()

获取当前实例的 TypeGets the Type of the current instance.

(继承自 Object)
IsDefaultAttribute()

在派生类中重写时,指示此实例的值是否是派生类的默认值。When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.

(继承自 Attribute)
Match(Object)

当在派生类中重写时,返回一个指示此实例是否等于指定对象的值。When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.

(继承自 Attribute)
MemberwiseClone()

创建当前 Object 的浅表副本。Creates a shallow copy of the current Object.

(继承自 Object)
ToString()

返回表示当前对象的字符串。Returns a string that represents the current object.

(继承自 Object)

显式接口实现

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

将一组名称映射为对应的一组调度标识符。Maps a set of names to a corresponding set of dispatch identifiers.

(继承自 Attribute)
_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

检索对象的类型信息,然后可以使用该信息获取接口的类型信息。Retrieves the type information for an object, which can be used to get the type information for an interface.

(继承自 Attribute)
_Attribute.GetTypeInfoCount(UInt32)

检索对象提供的类型信息接口的数量(0 或 1)。Retrieves the number of type information interfaces that an object provides (either 0 or 1).

(继承自 Attribute)
_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

提供对某一对象公开的属性和方法的访问。Provides access to properties and methods exposed by an object.

(继承自 Attribute)

适用于