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.
Assembly: mscorlib (in mscorlib.dll)
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.AttributeA reference to the single custom attribute of type attributeType that is applied to element, or null if there is no such attribute.
| Exception | Condition |
|---|---|
| ArgumentNullException | element or attributeType is null. |
| 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 System; using System.Reflection; namespace NDP_UE_CS { // Define a custom parameter attribute that takes a single message argument. [AttributeUsage( AttributeTargets.Parameter )] public class ArgumentUsageAttribute : Attribute { // This is the attribute constructor. public ArgumentUsageAttribute( string UsageMsg ) { this.usageMsg = UsageMsg; } // usageMsg is storage for the attribute message. protected string usageMsg; // This is the Message property for the attribute. public string Message { get { return usageMsg; } set { usageMsg = value; } } } public class BaseClass { // Assign an ArgumentUsage attribute to the strArray parameter. // Assign a ParamArray attribute to strList using the params keyword. public virtual void TestMethod( [ArgumentUsage("Must pass an array here.")] String[] strArray, params String[] strList) { } } public class DerivedClass : BaseClass { // Assign an ArgumentUsage attribute to the strList parameter. // Assign a ParamArray attribute to strList using the params keyword. public override void TestMethod( String[] strArray, [ArgumentUsage("Can pass a parameter list or array here.")] params String[] strList) { } } class CustomParamDemo { static void 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 = typeof( DerivedClass ); MethodInfo mInfo = clsType.GetMethod("TestMethod"); // Iterate through the ParameterInfo array for the method parameters. ParameterInfo[] pInfoArray = mInfo.GetParameters(); if (pInfoArray != null) { foreach( ParameterInfo paramInfo in pInfoArray ) { // See if the ParamArray attribute is defined. bool isDef = Attribute.IsDefined( paramInfo, typeof(ParamArrayAttribute)); if( isDef ) Console.WriteLine( "\nThe ParamArray attribute is defined " + "for \nparameter {0} of method {1}.", paramInfo.Name, mInfo.Name); // See if ParamUsageAttribute is defined. // If so, display a message. ArgumentUsageAttribute usageAttr = (ArgumentUsageAttribute) Attribute.GetCustomAttribute( paramInfo, typeof(ArgumentUsageAttribute) ); if( usageAttr != null ) { Console.WriteLine( "\nThe ArgumentUsage attribute is defined " + "for \nparameter {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.". */
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0