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ExportAttribute Class

Specifies that a type, property, field, or method provides a particular export.

System.Object
  System.Attribute
    System.ComponentModel.Composition.ExportAttribute
      System.ComponentModel.Composition.InheritedExportAttribute

Namespace:  System.ComponentModel.Composition
Assembly:  System.ComponentModel.Composition (in System.ComponentModel.Composition.dll)

'Declaration
<AttributeUsageAttribute(AttributeTargets.Class Or AttributeTargets.Method Or AttributeTargets.Property Or AttributeTargets.Field, AllowMultiple := True,  _
	Inherited := False)> _
Public Class ExportAttribute _
	Inherits Attribute

The ExportAttribute type exposes the following members.

  NameDescription
Public methodSupported by Portable Class LibraryExportAttributeInitializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under the default contract name.
Public methodSupported by Portable Class LibraryExportAttribute(String)Initializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under the specified contract name.
Public methodSupported by Portable Class LibraryExportAttribute(Type)Initializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under a contract name derived from the specified type.
Public methodSupported by Portable Class LibraryExportAttribute(String, Type)Initializes a new instance of the ExportAttribute class, exporting the specified type under the specified contract name.
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  NameDescription
Public propertySupported by Portable Class LibraryContractNameGets the contract name that is used to export the type or member marked with this attribute.
Public propertySupported by Portable Class LibraryContractTypeGets the contract type that is exported by the member that this attribute is attached to.
Public propertyTypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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  NameDescription
Public methodSupported by Portable Class LibraryEqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Protected methodSupported by Portable Class LibraryFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by Portable Class LibraryGetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public methodSupported by Portable Class LibraryGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodIsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public methodMatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Protected methodSupported by Portable Class LibraryMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSupported by Portable Class LibraryToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Explicit interface implemetationPrivate method_Attribute.GetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.InvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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In the Attributed Programming Model, the ExportAttribute declares that a part exports, or provides to the composition container, an object that fulfills a particular contract. During composition, parts with imports that have matching contracts will have those dependencies filled by the exported object.

The ExportAttribute can decorate either an entire class, or a property, field, or method of a class. If the entire class is decorated, an instance of the class is the exported object. If a member of a class is decorated, the exported object will be the value of the decorated member.

Whether or not a contract matches is determined primarily by the contract name and the contract type. For more information, see ImportAttribute.

The following example shows three classes decorated with the ExportAttribute, and three imports that match them.

    'Default export infers type and contract name from the 
    'exported type.  This is the preferred method.
    <Export()>
    Public Class MyExport1
        Public ReadOnly Property data As String 
            Get 
                Return "Test Data 1." 
            End Get 
        End Property 
    End Class 

    Public Class MyImporter1

        <Import()>
        Public Property ImportedMember As MyExport1

    End Class 

    Public Interface MyInterface

    End Interface 

    'Specifying the contract type may be important if 
    'you want to export a type other then the base type, 
    'such as an interface.
    <Export(GetType(MyInterface))>
    Public Class MyExport2
        Implements MyInterface
        Public ReadOnly Property data As String 
            Get 
                Return "Test Data 2." 
            End Get 
        End Property 
    End Class 

    Public Class MyImporter2
        'The import must match the contract type!
        <Import(GetType(MyInterface))>
        Public Property ImportedMember As MyExport2
    End Class 

    'Specifying a contract name should only be  
    'needed in rare caes. Usually, using metadata 
    'is a better approach.
    <Export("MyContractName", GetType(MyInterface))>
    Public Class MyExport3
        Implements MyInterface
        Public ReadOnly Property data As String 
            Get 
                Return "Test Data 3." 
            End Get 
        End Property 
    End Class 

    Public Class MyImporter3
        'Both contract name and type must match!
        <Import("MyContractName", GetType(MyInterface))>
        Public Property ImportedMember As MyExport3
    End Class 



    Sub Main()
        Dim catalog As AggregateCatalog = New AggregateCatalog()
        catalog.Catalogs.Add(New AssemblyCatalog(GetType(MyExport1).Assembly))
        Dim container As CompositionContainer = New CompositionContainer(catalog)
        Dim test1 As MyImporter1 = New MyImporter1()
        Dim test2 As MyImporter2 = New MyImporter2()
        Dim test3 As MyImporter3 = New MyImporter3()
        container.SatisfyImportsOnce(test1)
        container.SatisfyImportsOnce(test2)
        container.SatisfyImportsOnce(test3)
        Console.WriteLine(test1.ImportedMember.data)
        Console.WriteLine(test2.ImportedMember.data)
        Console.WriteLine(test3.ImportedMember.data)
        Console.ReadLine()
    End Sub

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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