ExportAttribute Class

.NET Framework (current version)
 

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

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

System.Object
System.Attribute
System.Composition.ExportAttribute

[AttributeUsageAttribute(AttributeTargets.Class | AttributeTargets.Property, 
	AllowMultiple = true, Inherited = false)]
public class ExportAttribute : Attribute

NameDescription
System_CAPS_pubmethodExportAttribute()

Initializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under the default contract name.

System_CAPS_pubmethodExportAttribute(String)

Initializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under the specified contract name.

System_CAPS_pubmethodExportAttribute(String, Type)

Initializes a new instance of the ExportAttribute class, exporting the specified type under the specified contract name.

System_CAPS_pubmethodExportAttribute(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.

NameDescription
System_CAPS_pubpropertyContractName

Gets the contract name that is used to export the type or member marked with this attribute.

System_CAPS_pubpropertyContractType

Gets the contract type that is exported by the member that is marked by this attribute.

System_CAPS_pubpropertyTypeId

(Inherited from Attribute.)

NameDescription
System_CAPS_pubmethodEquals(Object)

(Inherited from Attribute.)

System_CAPS_protmethodFinalize()

(Inherited from Object.)

System_CAPS_pubmethodGetHashCode()

(Inherited from Attribute.)

System_CAPS_pubmethodGetType()

(Inherited from Object.)

System_CAPS_pubmethodIsDefaultAttribute()

(Inherited from Attribute.)

System_CAPS_pubmethodMatch(Object)

(Inherited from Attribute.)

System_CAPS_protmethodMemberwiseClone()

(Inherited from Object.)

System_CAPS_pubmethodToString()

(Inherited from Object.)

In the attributed programming model, the ExportAttribute attribute 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 have those dependencies filled by the exported object.

The ExportAttribute attribute can apply to either an entire class, or a property, field, or method of a class. If it's applied to the entire class, an instance of the class is the exported object. If it's applied to a member of a class, the exported object will be the value of that member.

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

The following example shows ExportAttribute being applied to three classes, 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 String data = "Test Data 1.";
}

public class MyImporter1
{
    [Import]
    public MyExport1 importedMember { get; set; }
}

public interface MyInterface
{

}

//Specifying the contract type may be important if
//you want to export a type other then the base type,
//such as an interface.
[Export(typeof(MyInterface))]
public class MyExport2 : MyInterface
{
    public String data = "Test Data 2.";
}

public class MyImporter2
{
    //The import must match the contract type!
    [Import(typeof(MyInterface))]
    public MyExport2 importedMember { get; set; }
}

//Specifying a contract name should only be 
//needed in rare caes. Usually, using metadata
//is a better approach.
[Export("MyContractName", typeof(MyInterface))]
public class MyExport3 : MyInterface
{
    public String data = "Test Data 3.";
}

public class MyImporter3
{
    //Both contract name and type must match!
    [Import("MyContractName", typeof(MyInterface))]
    public MyExport3 importedMember { get; set; }
}

class Program
{      

    static void Main(string[] args)
    {
        AggregateCatalog catalog = new AggregateCatalog();
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(MyExport1).Assembly));
        CompositionContainer _container = new CompositionContainer(catalog);
        MyImporter1 test1 = new MyImporter1();
        MyImporter2 test2 = new MyImporter2();
        MyImporter3 test3 = 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();

    }
}

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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