How to recomposit empty DirectoryCatalog for MEF in WPF

Question

I have an application with these step:

1. startup application and ConfigureAggregateCatalog
2. logon user to app
3. download DLL MEF modules to directory called 'Modules'
4. refresh directory catalog -- there is a problem

I have empty directory 'Modules' after download dll i tried to load modules but without succes. There is an error on line where I called DirectoryCatalog.Refresh()

System.ComponentModel.Composition.ChangeRejectedException was unhandled by user code Message=The composition remains unchanged. The changes were rejected because of the following error(s): The composition produced multiple composition errors, with 14 root causes. The root causes are provided below. Review the CompositionException.Errors property for more detailed information.

1) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleInitializer..ctor (Parameter="downloadedPartCatalogs", ContractName="Microsoft.Practices.Prism.MefExtensions.Modularity.DownloadedPartCatalogCollection")' on part 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleInitializer'.

2) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager.mefFileModuleTypeLoader (ContractName="Microsoft.Practices.Prism.MefExtensions.Modularity.MefFileModuleTypeLoader")' on part 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager'.

3) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager..ctor (Parameter="moduleInitializer", ContractName="Microsoft.Practices.Prism.Modularity.IModuleInitializer")' on part 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager'.

4) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager.mefFileModuleTypeLoader (ContractName="Microsoft.Practices.Prism.MefExtensions.Modularity.MefFileModuleTypeLoader")' on part 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager'.

5) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager..ctor (Parameter="moduleInitializer", ContractName="Microsoft.Practices.Prism.Modularity.IModuleInitializer")' on part 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager'.

6) Change in exports prevented by non-recomposable import 'GXBilling.ViewsModels.ShellViewModel.ModuleManager (ContractName="Microsoft.Practices.Prism.Modularity.IModuleManager")' on part 'GXBilling.ViewsModels.ShellViewModel'.

7) More than one export was found that matches the constraint '((exportDefinition.ContractName == "Microsoft.Practices.Prism.Regions.RegionAdapterMappings") AndAlso (exportDefinition.Metadata.ContainsKey("ExportTypeIdentity") AndAlso "Microsoft.Practices.Prism.Regions.RegionAdapterMappings".Equals(exportDefinition.Metadata.get_Item("ExportTypeIdentity"))))'.

Resulting in: Cannot set import 'Microsoft.Practices.Prism.MefExtensions.Regions.Behaviors.MefDelayedRegionCreationBehavior..ctor (Parameter="regionAdapterMappings", ContractName="Microsoft.Practices.Prism.Regions.RegionAdapterMappings")' on part 'Microsoft.Practices.Prism.MefExtensions.Regions.Behaviors.MefDelayedRegionCreationBehavior'. Element: Microsoft.Practices.Prism.MefExtensions.Regions.Behaviors.MefDelayedRegionCreationBehavior..ctor (Parameter="regionAdapterMappings", ContractName="Microsoft.Practices.Prism.Regions.RegionAdapterMappings") --> Microsoft.Practices.Prism.MefExtensions.Regions.Behaviors.MefDelayedRegionCreationBehavior --> AssemblyCatalog (Assembly="Microsoft.Practices.Prism.MefExtensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")

8) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Regions.MefSelectorRegionAdapter..ctor (Parameter="regionBehaviorFactory", ContractName="Microsoft.Practices.Prism.Regions.IRegionBehaviorFactory")' on part 'Microsoft.Practices.Prism.MefExtensions.Regions.MefSelectorRegionAdapter'.

9) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Regions.MefItemsControlRegionAdapter..ctor (Parameter="regionBehaviorFactory", ContractName="Microsoft.Practices.Prism.Regions.IRegionBehaviorFactory")' on part 'Microsoft.Practices.Prism.MefExtensions.Regions.MefItemsControlRegionAdapter'.

10) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Regions.MefContentControlRegionAdapter..ctor (Parameter="regionBehaviorFactory", ContractName="Microsoft.Practices.Prism.Regions.IRegionBehaviorFactory")' on part 'Microsoft.Practices.Prism.MefExtensions.Regions.MefContentControlRegionAdapter'.

11) More than one export was found that matches the constraint '((exportDefinition.ContractName == "Microsoft.Practices.Prism.Regions.IRegionViewRegistry") AndAlso (exportDefinition.Metadata.ContainsKey("ExportTypeIdentity") AndAlso "Microsoft.Practices.Prism.Regions.IRegionViewRegistry".Equals(exportDefinition.Metadata.get_Item("ExportTypeIdentity"))))'.

Resulting in: Cannot set import 'Microsoft.Practices.Prism.MefExtensions.Regions.Behaviors.MefAutoPopulateRegionBehavior..ctor (Parameter="regionViewRegistry", ContractName="Microsoft.Practices.Prism.Regions.IRegionViewRegistry")' on part 'Microsoft.Practices.Prism.MefExtensions.Regions.Behaviors.MefAutoPopulateRegionBehavior'. Element: Microsoft.Practices.Prism.MefExtensions.Regions.Behaviors.MefAutoPopulateRegionBehavior..ctor (Parameter="regionViewRegistry", ContractName="Microsoft.Practices.Prism.Regions.IRegionViewRegistry") --> Microsoft.Practices.Prism.MefExtensions.Regions.Behaviors.MefAutoPopulateRegionBehavior --> AssemblyCatalog (Assembly="Microsoft.Practices.Prism.MefExtensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35")

12) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleInitializer..ctor (Parameter="downloadedPartCatalogs", ContractName="Microsoft.Practices.Prism.MefExtensions.Modularity.DownloadedPartCatalogCollection")' on part 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleInitializer'.

13) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager.mefFileModuleTypeLoader (ContractName="Microsoft.Practices.Prism.MefExtensions.Modularity.MefFileModuleTypeLoader")' on part 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager'.

14) Change in exports prevented by non-recomposable import 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager..ctor (Parameter="moduleInitializer", ContractName="Microsoft.Practices.Prism.Modularity.IModuleInitializer")' on part 'Microsoft.Practices.Prism.MefExtensions.Modularity.MefModuleManager'.

Source=System.ComponentModel.Composition StackTrace: at System.ComponentModel.Composition.CompositionResult.ThrowOnErrors(AtomicComposition atomicComposition) at System.ComponentModel.Composition.Hosting.ExportProvider.OnExportsChanging(ExportsChangeEventArgs e) at System.ComponentModel.Composition.Hosting.CatalogExportProvider.OnCatalogChanging(Object sender, ComposablePartCatalogChangeEventArgs e) at System.ComponentModel.Composition.Hosting.ComposablePartCatalogCollection.OnChanging(Object sender, ComposablePartCatalogChangeEventArgs e) at System.ComponentModel.Composition.Hosting.AggregateCatalog.OnChanging(ComposablePartCatalogChangeEventArgs e) at System.ComponentModel.Composition.Hosting.ComposablePartCatalogCollection.OnContainedCatalogChanging(Object sender, ComposablePartCatalogChangeEventArgs e) at System.ComponentModel.Composition.Hosting.DirectoryCatalog.OnChanging(ComposablePartCatalogChangeEventArgs e) at System.ComponentModel.Composition.Hosting.DirectoryCatalog.Refresh() at GXBilling.Bootstrapper.RefreshCatalog() in E:\Projects!New!\GXBilling\GXBilling\Bootstrapper.cs:line 36 at GXBilling.ViewsModels.WinLogOnViewModel.FWCore_OnDownloadedModulesCompleted(Object sender, EventArgs e) in E:\Projects!New!\GXBilling\GXBilling\ViewsModels\WinLogOnViewModel.cs:line 168 at BillingCore.FWCore.FWCore_ModuleDownloadedCompleted(Object sender, ModuleDownloadedEventArgs e) in E:\Projects!New!\GXBilling\BillingCore\FWCore.cs:line 169 at BillingCore.FWCore.client_DownloadFileCompleted(Object sender, DownloadFileCompletedEventArgs e) in E:\Projects!New!\GXBilling\BillingCore\FWCore.cs:line 207 at BillingCore.BillingServiceRef.FileTransferServiceClient.OnDownloadFileCompleted(Object state) in E:\Projects!New!\GXBilling\BillingCore\Service References\BillingServiceRef\Reference.cs:line 739 at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.DispatcherOperation.InvokeImpl() at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state) at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Threading.DispatcherOperation.Invoke() at System.Windows.Threading.Dispatcher.ProcessQueue() at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame) at System.Windows.Window.ShowHelper(Object booleanBox) at System.Windows.Window.Show() at System.Windows.Window.ShowDialog() InnerException:

There is parts of code marked by attribute Import:

[Import]
public ShellViewModel ViewModel

[Import(AllowRecomposition = false)]
public IModuleManager ModuleManager { get; set; }

[Import(typeof(IShell), AllowRecomposition = true)]
public IShell MainShell { get; set; }

[ImportingConstructor]
public ModuleImporting(IRegionManager regionManager)

That's all. I have not IEnureable or IList or etc. In code. So where is problem?

Answer 1

Whenever there is error like :

"Activation error occurred while trying to get instance of type , key "" "

Then please check whether [Export] attribute is specified in <User Control page> that we are going to inject in Region.

It is small thing but can waste you hours in debugging!

Thanks! Bassi

Answer 2

Refreshing the DirectoryCatalog triggers a recomposition. An import on a MEF part can only be recomposed if it is explicitly marked as such, for example like this:

[ImportMany(typeof(IFoo),AllowRecomposition=true)]
IEnumerable<IFoo> Foos { private get; set; }

If an import is affected by the recomposition, but it isn't marked with AllowRecomposition=true, then you get an error: "Change in exports prevented by non-recomposable import".

Also, imports via a constructor don't support recomposition at all. However, you can work around this.