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POIssue With Custom Collection Model Binder in MVC 3
 

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  1. POIssue With Custom Collection Model Binder in MVC 3
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    <p>I'm having an issue creating a model binder in MVC.</p> <p>The action that I'm targeting looks like:</p> <pre><code>public ActionResult GetAccounts (ICollection&lt;Account&gt; accounts ){} </code></pre> <p>I created a custom model binder and registered it with the following code:</p> <pre><code>ModelBinders.Binders.Add(typeof(ICollection&lt;Account&gt;),new CollectionModelBinder()); </code></pre> <p>With a debugger attached, I can see that the <code>CollectionModelBinder's CreateModel</code> method is being called. However, when execution reaches the action method of the controller, the accounts parameter is null.</p> <p>What's the issue?</p> <p>My model binder looks like:</p> <pre><code>public class CollectionModelBinder : DefaultModelBinder { protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType) { return new List&lt;Account&gt; { new Account {Id = 1}, new Account {Id = 2}, new Account {Id = 3}}; } } </code></pre> <p><strong>UPDATE:</strong></p> <p>This was a problem with <code>DefaultModelBinder.</code> After <code>CreateModel</code> was called, another internal method, <code>UpdateCollection</code> was called, which effectively nulled out the collection that was created by <code>CreateModel.</code> The solution was to roll my own implementation of <code>IModelBinder.</code> The only argument that's missing on <code>IModelBinder.BindModel</code> is the <code>modelType,</code> which is easy to get:</p> <pre><code>public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) { var type = bindingContext.ModelType; //... } </code></pre>
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    1. USJeremy Durnell
    1. USJeremy Durnell
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