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Attribute.IsDefined Method (Assembly, Type)


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Determines whether any custom attributes are applied to an assembly. Parameters specify the assembly, and the type of the custom attribute to search for.

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

public static bool IsDefined(
	Assembly element,
	Type attributeType


Type: System.Reflection.Assembly

An object derived from the Assembly class that describes a reusable collection of modules.

Type: System.Type

The type, or a base type, of the custom attribute to search for.

Return Value

Type: System.Boolean

true if a custom attribute of type attributeType is applied to element; otherwise, false.

Exception Condition

element or attributeType is null.


attributeType is not derived from Attribute.


Starting with the .NET Framework version 2.0, this method returns true if the assembly has security attributes stored in the new metadata format. Assemblies compiled with version 2.0 or later use the new format. Dynamic assemblies and assemblies compiled with earlier versions of the .NET Framework use the old XML format. See Emitting Declarative Security Attributes.

The following code example illustrates the use of IsDefined, taking an Assembly as a parameter.

using System;
using System.Reflection;

// Add an AssemblyDescription attribute
[assembly: AssemblyDescription("A sample description")]
namespace IsDef1CS
    public class DemoClass
        static void Main(string[] args)
            // Get the class type to access its metadata.
            Type clsType = typeof(DemoClass);
            // Get the assembly object.
            Assembly assy = clsType.Assembly;
            // Store the assembly's name.
            String assyName = assy.GetName().Name;
            // See if the Assembly Description is defined.
            bool isdef = Attribute.IsDefined(assy, 
            if (isdef)
                // Affirm that the attribute is defined.
                Console.WriteLine("The AssemblyDescription attribute " +
                    "is defined for assembly {0}.", assyName);
                // Get the description attribute itself.
                AssemblyDescriptionAttribute adAttr = 
                    assy, typeof(AssemblyDescriptionAttribute));
                // Display the description.
                if (adAttr != null)
                    Console.WriteLine("The description is \"{0}\".", 
                    Console.WriteLine("The description could not " +
                        "be retrieved.");            
                Console.WriteLine("The AssemblyDescription attribute is not " +
                    "defined for assembly {0}.", assyName);

 * Output:
 * The AssemblyDescription attribute is defined for assembly IsDef1CS.
 * The description is "A sample description".

.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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