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ExportAttribute Class

.NET Framework 4.6 and 4.5

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

System.Object
  System.Attribute
    System.Composition.ExportAttribute

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

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

The ExportAttribute type exposes the following members.

  NameDescription
Public methodExportAttribute()Initializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under the default contract name.
Public methodExportAttribute(String)Initializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under the specified contract name.
Public methodExportAttribute(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 methodExportAttribute(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 propertyContractNameGets the contract name that is used to export the type or member marked with this attribute.
Public propertyContractTypeGets the contract type that is exported by the member that is marked by this attribute.
Public propertyTypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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  NameDescription
Public methodEqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public methodGetTypeGets 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 methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns 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 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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