Question

I have:
1)

public class Model
{
    public String Name { get; set; }
    public SubModel SubModel { get; set; }
}  

2)

public SubModel
{
    public String Title { get; set; }
}

3) Model-typed ModelViewUserControl
4) SubModel-typed SubModelViewUserControl
5) Page

I need:
Show on the Page 2 TextBoxes: for Model.Name and Model.SubModel.Title.

I do:
1) In Page:

<% Html.RenderPartial("ModelViewUserControl", Model); %>

2) In ModelViewUserControl:

<%= Html.TextBoxFor(m => m.Name) %>
<% Html.RenderPartial("SubModelViewUserControl", Model.SubModel); %>

3) In SubModelViewUserControl:

<%= Html.TextBoxFor(m => m.Title) %>

Result is
In Controller’s method I have Model.Name == “Bla” but Model.SubModel == null.
Of course, I use Html.BeginForm().

HTML:

<input id="Name" name="Name" type="text" value="" />
<input id="Title" name="Title" type="text" value="" />

Answer 1

Instead of using RenderPartial I would recommend you using editor templates which will make your life easier:

In the main View:

<% using (Html.BeginForm()) { %>
    <%= Html.EditorForModel() %>
    <input type="submit" value="OK" />
<% } %>

Editor template for the model (~/Views/Shared/EditorTemplates/Model.ascx):

<%= Html.TextBoxFor(x => x.Name) %>
<%= Html.EditorFor(x => x.SubModel) %>

Editor template for the SubModel (~/Views/Shared/EditorTemplates/SubModel.ascx):

<%= Html.TextBoxFor(m => m.Title) %>