ExportAttribute Class
Definition
Important
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Specifies that a type, property, field, or method provides a particular export.
public ref class ExportAttribute : Attribute[System.AttributeUsage(System.AttributeTargets.Class | System.AttributeTargets.Property, AllowMultiple=true, Inherited=false)]
public class ExportAttribute : Attribute[<System.AttributeUsage(System.AttributeTargets.Class | System.AttributeTargets.Property, AllowMultiple=true, Inherited=false)>]
type ExportAttribute = class
inherit AttributePublic Class ExportAttribute
Inherits Attribute- Inheritance
- Attributes
Examples
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 cases. 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();
}
}
'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 cases. 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
Remarks
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.
Constructors
| ExportAttribute() |
Initializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under the default contract name. |
| ExportAttribute(String, Type) |
Initializes a new instance of the ExportAttribute class, exporting the specified type under the specified contract name. |
| ExportAttribute(String) |
Initializes a new instance of the ExportAttribute class, exporting the type or member marked with this attribute under the specified contract name. |
| ExportAttribute(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. |
Properties
| ContractName |
Gets the contract name that is used to export the type or member marked with this attribute. |
| ContractType |
Gets the contract type that is exported by the member that is marked by this attribute. |
| TypeId |
When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute) |
Methods
| Equals(Object) |
Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute) |
| GetHashCode() |
Returns the hash code for this instance. (Inherited from Attribute) |
| GetType() |
Gets the Type of the current instance. (Inherited from Object) |
| IsDefaultAttribute() |
When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute) |
| Match(Object) |
When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute) |
| MemberwiseClone() |
Creates a shallow copy of the current Object. (Inherited from Object) |
| ToString() |
Returns a string that represents the current object. (Inherited from Object) |
