title: Model Warnings in ASP.NET MVC
body: <p>I'm currently using the ModelStateDictionary in asp.net mvc to hold validation errors and pass then back to the user. Being able to check if the whole model is valid with ModelState.IsValid is particularly. However, a current application I'm working on has a need to be able to report warnings. These aren't as critical so the form content can still be saved, but they should be shown to the user so that action can be optionally taken.</p>
  
  <p>I've been looking through the framework to see if there are any obvious place to extend it to allow me to do this. I'm thinking that another dictionary with warnings in and a subclass of model error called model warning. I'm not sure how I'd get the framework to use my new container classes in the view etc. though, I still want all of the existing error stuff to work.</p>
  
  <p>If anyone has tried anything similar or has any thoughts I'd appreciate their input.</p>
  
  <p>Update:</p>
  
  <p>I've got as far as extending the ViewDataDictionary to add some warnings</p>
  
  <pre><code>public class AetherViewDataDictionary : ViewDataDictionary
  {
      public AetherViewDataDictionary()
      {
          ModelStateWarning = new ModelStateDictionary();
      }
  
      public AetherViewDataDictionary(object model) : base(model)
      {
          ModelStateWarning = new ModelStateDictionary();
      }
  
      public AetherViewDataDictionary(ViewDataDictionary viewDataDictionary) : base(viewDataDictionary) 
      {
          ModelStateWarning = new ModelStateDictionary();
      }
  
      public ModelStateDictionary ModelStateWarning { get; private set; }
  }
  </code></pre>
  
  <p>The problem that I'm having now is that when I get to my view code, this is just for debug I'm losing the fact that its my new type, so when I try to cast it back and get access to my new dictionary I have no joy.</p>
  
  <pre><code>public partial class Index : ViewPage&lt;PageViewData&gt;
  {
      protected override void SetViewData(ViewDataDictionary viewData)
      {
          base.SetViewData(viewData);
      }
  }
  </code></pre>
  
  <p>It sets it correctly here, but when I check the type its gone.</p>
  
  <p>Edit:
  This turned out to be a dumb way of doing things, see answer below.</p>