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    <p>As far as your example is concerned, you can think of <code>IEnumerable&lt;T&gt;</code> as being pretty much synonymous with <code>List&lt;T&gt;</code>: it's a collection of objects; it could be just one, it could be none, it could be a hundred. There's more to <code>IEnumerable</code> than that, but for your purposes that's as much as you need to think about.</p> <p>In this code:</p> <pre><code>[ImportMany] public IEnumerable&lt;IEmailAddressesProvider&gt; AddressProviders { get; set; } </code></pre> <p>you're asking MEF to gather all the exported implementations of <code>IEmailAddressesProvider</code>. What you get back is a collection of objects: even if it finds just one, you still get a collection with only one element. In this later line:</p> <pre><code>ev.ViewModel.ProviderName = AddressProviders; </code></pre> <p>I'm guessing that the left hand side is expecting a <code>string</code>, but the right hand side is a collection of <code>IEmailAddressesProvider</code>. Apart from the fact that you probably actually want the <code>ProviderName</code> property of the <code>IEmailAddressesProvider</code> and not the whole object, you also need to say which object in the collection to use. There are two ways you might deal with this:</p> <ol> <li><p><strong>If you know that there will only be one implementation of <code>IEmailAddressesProvider</code></strong>, then change <code>ImportMany</code> to <code>Import</code> like so</p> <pre><code>[Import] public IEmailAddressesProvider AddressProviders { get; set; } </code></pre> <p>and change that other assignment to <code>ev.ViewModel.ProviderName = AddressProviders.ProviderName</code>. Note that this will break as soon as you export a second implementation of <code>IEmailAddressesProvider</code>, so only do this if you really know there can only be one.</p></li> <li><strong>If there may be several implementations of <code>IEmailAddressesProvider</code></strong>, then you need to find the specific one you want. You would query the <code>AddressProviders</code> collection with something like <code>FirstOrDefault</code> (as the other answers have said) to find the right object and then use the <code>ProviderName</code> property from that result. It's not possible to say much more about the query you need from the code you've provided.</li> </ol>
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    1. COI was trying to implement this code: I receive this error: Error 24 'System.Collections.Generic.IEnumerable<Alliance.Library.Email.IEmailAddressesProvider>' does not contain a definition for 'ProviderName' and no extension method 'ProviderName' accepting a first argument of type 'System.Collections.Generic.IEnumerable<Alliance.Library.Email.IEmailAddressesProvider>' could be found (are you missing a using directive or an assembly reference?) C:\TFS-Alliance\Suite\Main\Source\Core\Core\Services\EmailService.cs 88 58 Core (Common\Core\Core)
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    2. COSorry for the bad formatting!
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    3. COWhich of the two were you trying to implement - option #1 or #2?
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