MEF程序设计指南七：使用目录（Catalog）动态装载xap与目录筛选（Filtered Catalog）

public   void  AddXap( string  relativeUri, Action < AsyncCompletedEventArgs >  completedAction)
{
    DeploymentCatalog catalog;
     if  ( ! _catalogs.TryGetValue(relativeUri,  out  catalog))
    {
        catalog  =   new  DeploymentCatalog(relativeUri);

         if  (completedAction  !=   null )
            catalog.DownloadCompleted  +=  (s, e)  =>  completedAction(e);
         else
            catalog.DownloadCompleted  +=  DownloadCompleted;

        catalog.DownloadAsync();
        _catalogs[relativeUri]  =  catalog;
        _aggregateCatalog.Catalogs.Add(catalog);

    }
}

[Import]
public  IDeploymentService Service {  get ;  set ; }

private   void  button1_Click( object  sender, System.Windows.RoutedEventArgs e)
{
     this .Service.AddXap( " MEFTraining.MefCatalogs.Parts.xap " ,  null );
}

public   void  OnImportsSatisfied()
{
            
}

public   class  FilteredCatalog : ComposablePartCatalog, INotifyComposablePartCatalogChanged
{
     private   readonly  ComposablePartCatalog _inner;
     private   readonly  INotifyComposablePartCatalogChanged _innerNotifyChange;
     private   readonly  IQueryable < ComposablePartDefinition >  _partsQuery;

     public  FilteredCatalog(ComposablePartCatalog inner,
                        Expression < Func < ComposablePartDefinition,  bool >>  expression)
    {
        _inner  =  inner;
        _innerNotifyChange  =  inner  as  INotifyComposablePartCatalogChanged;
        _partsQuery  =  inner.Parts.Where(expression);
    }

     public   event  EventHandler < ComposablePartCatalogChangeEventArgs >  Changed
    {
        add
        {
             if  (_innerNotifyChange  !=   null )
                _innerNotifyChange.Changed  +=  value;
        }
        remove
        {
             if  (_innerNotifyChange  !=   null )
                _innerNotifyChange.Changed  -=  value;
        }

    }

     public   event  EventHandler < ComposablePartCatalogChangeEventArgs >  Changing
    {
        add
        {
             if  (_innerNotifyChange  !=   null )
                _innerNotifyChange.Changing  +=  value;
        }
        remove
        {
             if  (_innerNotifyChange  !=   null )
                _innerNotifyChange.Changing  -=  value;
        }

    }

     public   override  System.Linq.IQueryable < ComposablePartDefinition >  Parts
    {
         get
        {
             return  _partsQuery;
        }
    }
}

var filteredCat  =   new  FilteredCatalog(catalog,
    def  =>  def.Metadata.ContainsKey(CompositionConstants.PartCreationPolicyMetadataName)  &&
        ((CreationPolicy)def.Metadata[CompositionConstants.PartCreationPolicyMetadataName])  ==  CreationPolicy.NonShared);

[PartMetadata( " UC " ,  " AA " )]
[Export( typeof (UserControl))]
public   partial   class  AA : UserControl
{
     public  AA()
    {
        InitializeComponent();
    }
}

[PartMetadata( " UC " ,  " BB " )]
[Export( typeof (UserControl))]
public   partial   class  BB : UserControl
{
     public  BB()
    {
        InitializeComponent();
    }
}

[PartMetadata( " UC " ,  " CC " )]
[Export( typeof (UserControl))]
public   partial   class  CC : UserControl
{
     public  CC()
    {
        InitializeComponent();
    }
}

// 获取当前应用程序目录
var catalog  =   new  AssemblyCatalog( typeof (MainPage).Assembly);
// 将目录装载进MEF组合容器
var parent  =   new  CompositionContainer(catalog);
// 通过元数据过滤筛选出元数据名称为"UC"值为"CC"的组合部件
var filteredCat  =   new  FilteredCatalog(catalog,
    def  =>  def.Metadata.ContainsKey( " UC " )  &&
    def.Metadata[ " UC " ].ToString()  ==   " CC " );
var perRequest  =   new  CompositionContainer(filteredCat, parent);
var control  =  perRequest.GetExportedValue < UserControl > ();