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PONullReferenceException in MVC3 Controller
 

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  1. PONullReferenceException in MVC3 Controller
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    <p>I'm playing around with MVC3, trying to create small test projects which simulate problems that I anticipate I will encounter in a larger project I'm migrating from PHP. I keep getting a "NullReferenceException" on instantiating the "model" variable in the project with the elements below:</p> <p>Model:</p> <pre><code>public class MainModel { public IEnumerable&lt;Chemical&gt; chemicals { get; set; } } public class Chemical { public int ChemicalId { get; set; } public string Name { get; set; } public virtual ICollection&lt;Hazard&gt; Hazards { get; set; } } public class Hazard { public int HazardId { get; set; } public string Description { get; set; } public virtual ICollection&lt;Chemical&gt; Chemicals { get; set; } } </code></pre> <p>Controller:</p> <pre><code>public class MainController : Controller { public ActionResult Index() { var h1 = new Hazard { HazardId = 1, Description = "Flammable" }; var h2 = new Hazard { HazardId = 2, Description = "Carcinogen" }; var h3 = new Hazard { HazardId = 3, Description = "Water Reactive" }; var model = new [] { new Chemical { ChemicalId = 1, Name = "Benzene", Hazards = {h1, h2}}, new Chemical { ChemicalId = 2, Name = "Sodium", Hazards = { h3 } }, new Chemical { ChemicalId = 3, Name = "Chloroform", Hazards = { h2 } }, new Chemical { ChemicalId = 4, Name = "Water" } }; //NULL EXCEPTION THROWN HERE return View(model); } } </code></pre> <p>So, I have two questions:</p> <ol> <li>Why do I keep getting the NullReferenceException, and how could it be fixed?</li> <li>In writing this code, I used this <a href="https://stackoverflow.com/questions/4872192/checkboxlist-in-mvc3-0">StackOverFlow Page</a> as a starting point. Why is this okay, but what I wrote is not? Granted, I didn't test this code, but the author seems very competent.</li> </ol> <p>Thanks! </p>
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    1. USChemProfMatt
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    1. COPost your Index view please. I bet your Index view expects a Model of type "MainModel" while you pass a simple array of "Chemicals" to your Index view. I think you meant to instantiate a "MainModel" in your Controller action?
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      1. PONullReferenceException in MVC3 Controller
      1. USSimon
    2. COI agree with @Simon too; you're going to have another problem once your view gets rendered, because you're calling `View()` with an array of `Chemical[]`, not a `MainModel`. Fixing it would look like: `var model = new MainModel(){chemicals = new [] { ... chemicals ... }};`
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      1. PONullReferenceException in MVC3 Controller
      1. USScott Rippey
 

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