自定义DirectoryCatalog类处理ReflectionTypeLoadException

当我在MEF中使用DirectoryCatalog来实现对应用程序的扩展功能。使用的扩展类，可能会带入一些独立使用的引用DLL,这些DLL内不会存在扩展实现接口，此时在程序导入扩展模块时，会导致ReflectionTypeLoadException。

    实现方法是通过自定义DirectoryCatalog类处理ReflectionTypeLoadException或其他类似的异常

下面是实现代码示例

C#

public class SafeDirectoryCatalog : ComposablePartCatalog
{
    private readonly AggregateCatalog _catalog;

    public SafeDirectoryCatalog(string directory)
    {
        var files = Directory.EnumerateFiles(directory,"*.dll", SearchOption.AllDirectories);

        _catalog = new AggregateCatalog();

        foreach (var file in files)
        {
            try
            {
                var asmCat = new AssemblyCatalog(file);

                //Force MEF to load the plugin and figure out if there are any exports
                // good assemblies will not throw the RTLE exception and can be added to the catalog
                if (asmCat.Parts.ToList().Count > 0)
                    _catalog.Catalogs.Add(asmCat);
            }
            catch (ReflectionTypeLoadException)
            {
            }
            catch (BadImageFormatException)
            {
            }
        }
    }
    public override IQueryable<ComposablePartDefinition> Parts
    {
        get { return _catalog.Parts; }
    }
}

VB.Net

Public Class SafeDirectoryCatalog
    Inherits ComposablePartCatalog

    Private ReadOnly Property _catalog As AggregateCatalog

    Public Sub New(pDirectory As String)
        Dim files = Directory.EnumerateFiles(pDirectory, "*.dll", SearchOption.TopDirectoryOnly)

        _catalog = New AggregateCatalog()

        For Each file In files
            Try
                Dim asmCat = New AssemblyCatalog(file)
                If (asmCat.Parts.ToList().Count > 0) Then
                    _catalog.Catalogs.Add(asmCat)
                End If
            Catch ex As ReflectionTypeLoadException

            Catch ex As BadImageFormatException

            End Try
        Next

    End Sub

    Public Overrides ReadOnly Property Parts As IQueryable(Of ComposablePartDefinition)
        Get
            Return _catalog.Parts
        End Get
    End Property

End Class

调用例子

Dim pDirectoryCatalog As New SafeDirectoryCatalog("Plugins")        '增加对扩展目录的导入
pCatalogAggregate.Catalogs.Add(pDirectoryCatalog)
mPluginsMEFContainer = New CompositionContainer(pCatalogAggregate)