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Attribute::GetCustomAttribute Method (ParameterInfo, Type)

Retrieves a custom attribute applied to a method parameter. Parameters specify the method parameter, and the type of the custom attribute to search for.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public:
static Attribute^ GetCustomAttribute(
	ParameterInfo^ element, 
	Type^ attributeType
)

Parameters

element
Type: System.Reflection::ParameterInfo
An object derived from the ParameterInfo class that describes a parameter of a member of a class.
attributeType
Type: System::Type
The type, or a base type, of the custom attribute to search for.

Return Value

Type: System::Attribute
A reference to the single custom attribute of type attributeType that is applied to element, or nullptr if there is no such attribute.

ExceptionCondition
ArgumentNullException

element or attributeType is nullptr.

ArgumentException

attributeType is not derived from Attribute.

AmbiguousMatchException

More than one of the requested attributes was found.

TypeLoadException

A custom attribute type cannot be loaded.

If element represents a parameter in a method of a derived type, the return value includes the inheritable custom attributes applied to the same parameter in the overridden base methods.

The following code example defines a custom parameter Attribute class and applies the custom attribute to a method in a derived class and the base of the derived class. The example shows the use of the GetCustomAttribute method to return the attributes.


// Example for the Attribute::GetCustomAttribute( ParameterInfo*, Type* ) 
// method.
using namespace System;
using namespace System::Collections;
using namespace System::Reflection;

namespace NDP_UE_CPP
{

   // Define a custom parameter attribute that takes a single message argument.

   [AttributeUsage(AttributeTargets::Parameter)]
   public ref class ArgumentUsageAttribute: public Attribute
   {
   protected:

      // usageMsg is storage for the attribute message.
      String^ usageMsg;

   public:

      // This is the attribute constructor.
      ArgumentUsageAttribute( String^ UsageMsg )
      {
         this->usageMsg = UsageMsg;
      }


      property String^ Message 
      {
         // This is the Message property for the attribute.
         String^ get()
         {
            return usageMsg;
         }

         void set( String^ value )
         {
            this->usageMsg = value;
         }
      }
   };

   public ref class BaseClass
   {
   public:

      // Assign an ArgumentUsage attribute to the strArray parameter.
      // Assign a ParamArray attribute to strList.
      virtual void TestMethod( [ArgumentUsage("Must pass an array here.")]array<String^>^strArray,
                               ...array<String^>^strList ){}
   };

   public ref class DerivedClass: public BaseClass
   {
   public:

      // Assign an ArgumentUsage attributes to the strList parameter.
      virtual void TestMethod( array<String^>^strArray, [ArgumentUsage(
      "Can pass a parameter list or array here.")]array<String^>^strList ) override {}
   };
}

int main()
{
   Console::WriteLine( "This example of Attribute::GetCustomAttribute( Param"
   "eterInfo*, Type* )\ngenerates the following output." );

   // Get the class type, and then get the MethodInfo object 
   // for TestMethod to access its metadata.
   Type^ clsType = NDP_UE_CPP::DerivedClass::typeid;
   MethodInfo^ mInfo = clsType->GetMethod( "TestMethod" );

   // Iterate through the ParameterInfo array for the method parameters.
   array<ParameterInfo^>^pInfoArray = mInfo->GetParameters();
   if ( pInfoArray != nullptr )
   {
      // This implements foreach( ParameterInfo* paramInfo in pInfoArray ).
      IEnumerator^ myEnum = pInfoArray->GetEnumerator();
      while ( myEnum->MoveNext() )
      {
         ParameterInfo^ paramInfo = safe_cast<ParameterInfo^>(myEnum->Current);

         // See if the ParamArray attribute is defined.
         bool isDef = Attribute::IsDefined( paramInfo, ParamArrayAttribute::typeid );
         if ( isDef )
                  Console::WriteLine( "\nThe ParamArray attribute is defined for \n"
         "parameter {0} of method {1}.", paramInfo->Name, mInfo->Name );

         // See if ParamUsageAttribute is defined.  
         // If so, display a message.
         NDP_UE_CPP::ArgumentUsageAttribute^ usageAttr = static_cast<NDP_UE_CPP::ArgumentUsageAttribute^>(Attribute::GetCustomAttribute( paramInfo, NDP_UE_CPP::ArgumentUsageAttribute::typeid ));
         if ( usageAttr != nullptr )
         {
            Console::WriteLine( "\nThe ArgumentUsage attribute is defined for \n"
            "parameter {0} of method {1}.", paramInfo->Name, mInfo->Name );
            Console::WriteLine( "\n    The usage "
            "message for {0} is:\n    \"{1}\".", paramInfo->Name, usageAttr->Message );
         }
      }
   }
   else
      Console::WriteLine( "The parameters information could "
   "not be retrieved for method {0}.", mInfo->Name );
}

/*
This example of Attribute::GetCustomAttribute( ParameterInfo*, Type* )
generates the following output.

The ArgumentUsage attribute is defined for
parameter strArray of method TestMethod.

    The usage message for strArray is:
    "Must pass an array here.".

The ParamArray attribute is defined for
parameter strList of method TestMethod.

The ArgumentUsage attribute is defined for
parameter strList of method TestMethod.

    The usage message for strList is:
    "Can pass a parameter list or array here.".
*/


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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