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POHow to export parts from an object not instantiated by the MEF container
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  1. POHow to export parts from an object not instantiated by the MEF container
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    copied!<h1>Introduction</h1> <p>Class <code>SessionModel</code> is a service locator providing several services (I am going to elaborate my system architecture in the future, but for now I need to do it that way).</p> <h1>Code</h1> <p>I edited the following code part to be a Short, Self Contained, Correct (Compilable), Example (SSCCE):</p> <pre class="lang-c# prettyprint-override"><code>using System; using System.ComponentModel.Composition; using System.ComponentModel.Composition.Hosting; namespace ConsoleApplication1 { internal class Program { private static void Main(string[] args) { var sessionModel = new SessionModel(3); // first case (see text down below): var compositionContainer = new CompositionContainer(); // second case (see text down below): //var typeCatalog = new TypeCatalog(typeof (SessionModel)); //var compositionContainer = new CompositionContainer(typeCatalog); compositionContainer.ComposeExportedValue(sessionModel); var someService = compositionContainer.GetExportedValue&lt;ISomeService&gt;(); someService.DoSomething(); } } public class SessionModel { private int AValue { get; set; } [Export] public ISomeService SomeService { get; private set; } public SessionModel(int aValue) { AValue = aValue; // of course, there is much more to do here in reality: SomeService = new SomeService(); } } public interface ISomeService { void DoSomething(); } public class SomeService : ISomeService { public void DoSomething() { Console.WriteLine("DoSomething called"); } } } </code></pre> <h1>Problem</h1> <p>I would like MEF to consider the parts (i.e. <code>SomeService</code>) exported by the service locator when composing other parts, but unfortunately this does not work.</p> <h2>First Case</h2> <p>When I try to get the exported value for <code>ISomeService</code> there is a <code>System.ComponentModel.Composition.ImportCardinalityMismatchException</code> telling me there are no exports with this contract name and required type identity (<code>ConsoleApplication1.ISomeService</code>).</p> <h2>Second Case</h2> <p>If I create the <code>CompositionContainer</code> using the <code>TypeCatalog</code> the exception is slightly different. It is a <code>System.ComponentModel.Composition.CompositionException</code> telling me MEF doesn't find a way to create a <code>ConsoleApplication1.SessionModel</code> (which is right and the reason why I am doing it myself).</p> <h1>Additional Information</h1> <p><code>mefx</code> says for both cases:</p> <pre><code>[Part] ConsoleApplication1.SessionModel from: DirectoryCatalog (Path=".") [Export] ConsoleApplication1.SessionModel.SomeService (ContractName="ConsoleApplication1.ISomeService") [Part] ConsoleApplication1.SessionModel from: AssemblyCatalog (Assembly="ConsoleApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null") [Export] ConsoleApplication1.SessionModel.SomeService (ContractName="ConsoleApplication1.ISomeService") </code></pre> <p>What do I have to do? Is this possible with MEF or do I have to use Unity or StructureMap, or something else? Can this be done implementing an <code>ExportProvider</code>?</p>
 

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