Related Attributes

These attributes are under namespace System.ComponentModel.Composition

• Import
  
  The attribute can be used on fields, properties, parameters. E.g. If a property is defined with the attribute, the property will be created automatically when the object is created.
  
  Example:

        [Import(RequiredCreationPolicy = CreationPolicy.NonShared)]

        public EmployeeGridViewModel Model

        {

            get

            {

                return this.Owner.DataContext as EmployeeGridViewModel;

            }

            set

            {

                this.Owner.DataContext = value;

            }

        }

• ImportingConstructor
  
  For previous example, how to create an instance of EmployeeGridViewModel? It will need attribute ImportingConstructor.

        [ImportingConstructor]

        public EmployeeGridViewModel(IEmployeeService employeeService)

        {

            this.employeeService = employeeService;

            ...

        }

• Export: This attribute is used to register a class into MEF.
  
  Next question is how to create an instance of IEmployeeService, look this:

    [Export(typeof(IEmployeeService))]

    [PartCreationPolicy(CreationPolicy.Shared)]

    public class EmployeeService : IEmployeeService

    {

    }

These code registers EmployeeService as an impelement of type IEmployeeService.

• PartCreationPolicy
  
  The attribtue is used with attribute Export, tell MEF the class creation policy, implment a singleton policy or create an instance always.