Here are some tips for MEF

Update: 5/27/2015

Index

• MEF as of .NET4 leaks memory
• How can I load a specific Export?
• How can I extract LoaderExceptions?

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MEF as of .NET4 leaks memory

We just found out that MEF of .NET 4 leaks memory due to the container never removes the reference. We found that our application memory usage kept increasing and at the end it ran out of memory. The details of why and how to avoid is described here. http://toreaurstad.blogspot.com/2012/09/freeing-up-memory-used-by-mef.html He also describes how MEF2 under .NET4.5 can solve the memory leak http://toreaurstad.blogspot.no/2013/07/mef-and-memory-in-mef-2.html.

Index

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How can I load a specific Export?

Sometimes you cannot use the assemblies in the executing directory.I wanted to resolve export only from a particular assembly.

  
  [Import]  
  IStatusLogger statusLogger = null;  
  ...  
  AggregateCatalog agg = new AggregateCatalog();  
  var statusCatalog = new AssemblyCatalog(typeof(ConsoleStatusLogger).Assembly);  
  var container = new CompositionContainer(agg);  
  try  
  {    
    statusLogger = container.GetExportedValue<IStatusLogger>();  
  }  
  catch(Exception ex)  
  {    
    var typeLoadException = ex as ReflectionTypeLoadException;    
	var loaderExceptions = typeLoadException.LoaderExceptions;    
	foreach (var item in loaderExceptions)    
	{      
	  Trace.WriteLine(item.Message);    
	}  
  }
  

Index

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How can I extract LoaderExceptios?

When I composing the exported object and try to get the import resolved, I got the following exception message:
Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.
It turned out thatin order to retrieve the LoaderExceptions, you have to know how to cast the exception object into the right object. Here is how.

   
  using System.Reflection;   
  ...   
  try   
  {   
  }   
  catch (Exception ex)   
  {     
    var typeLoadException = ex as ReflectionTypeLoadException;      
	var loaderExceptions = typeLoadException.LoaderExceptions;      
	string msg = string.Empty;     
	foreach (var item in loaderExceptions)     
	{       
	  msg += item.Message;       
	  msg += "\n";     
	}     
	// show message here   
  }
  

Index