Prism MEF example

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.