Simple fix for 'Cannot bind source type Umbraco.Web.Models.RenderModel to model type xx'

When calling @Html.Partial("MyPartialName", myModel), you might sometimes run into 'Cannot bind source type Umbraco.Web.Models.RenderModel to model type xx', it turns out that the solution to this issue might be a little simpler than you first thought.

What you shouldn't do (not the fix):

Your first thought might be to make your model inherit from RenderModel, but if you're doing everything the same as all your other partials and they don't have their models extend RenderModel, then chances are, that's not the issue. Don't do it. It'll be more work than you think to implement, you'll spend hours on it and it'll turn out that you need to remove it all again.

public class MyModel : RenderModel { ... all the other things that go with setting up a render model ... }

What's wrong?

If like me, you have a helper function to get your model for this particular instance, your issues could become obfuscated because that function might not be returning what you think it is. The error is a misleading one at best.

The Fix:

Make sure your model isn't null before using it as a parameter for Html.Partial. Seriously. The error is misleading because it reports your model is of the wrong type, technically it's true, but that's only because it's null. You could try something like the below:

MyModel objModel = SomeNamespace.GetModelFromPlace(myParams); // Might return null

if (objModel != null) // Only render partial of there's something to work with.
{
    @Html.Partial("MyPartial", myModel)
}

Or failing that, if you need to render the partial:

MyModel objModel = SomeNamespace.GetModelFromPlace(myParams); // Might return null.

if (objModel == null) // If model is null, just use a blank one.
{
    obj|Model = new MyModel();
}

@Html.Partial("MyPartial", myModel) // Sorted

Simple isn't it? Don't let the 'Cannot bind source type Umbraco.Web.Models.RenderModel to model type xx' error fool you.

Still not working? See other reasons it might not be working:

This guy was returning a view from a controller with the same error.