.net mvc view not return model on post

Question

Before i started i would like to say i searched and found nothing similar
in my solution i have a model that contains a list of some of my objects

public class ModelView
{
    public Owner owner = new Owner();
    public Tenant tnt = new Tenant();
}

In my view i call that class as a model which is this way

@model WebApp.Models.ModelView

<form name="export_form" action="Export" method="post">
    <table cellpadding="2" cellspacing="2" border="0">
        @if (Condition_1)
        { 
            <tr>
                <td>
                    <!-- ID -->
                </td>
                <td>
                    @Html.HiddenFor(model => model.owner.ID)
                </td>
            </tr>
            <tr>
                <td>
                    Name
                </td>
                <td>
                    @Html.EditorFor(model => model.owner.name)
                </td>
            </tr>
            <tr>
                <td>
                    Phone
                </td>
                <td>
                    @Html.CheckBoxFor(model => model.owner.is_Checked_Phone)
                </td>
            </tr>
        }
        else 
        {
            <tr>
                <td>
                    <!-- ID -->
                </td>
                <td>
                    @Html.HiddenFor(model => model.tnt.ID)
                </td>
            </tr>
            <tr>
                <td>
                    Name
                </td>
                <td>
                    @Html.EditorFor(model => model.tnt.name)
                </td>
            </tr>
            <tr>
                <td>
                    Adress
                </td>
                <td>
                    @Html.CheckBoxFor(model => model.tnt.is_Checked_Adress)
                </td>
            </tr>
        }
    </table>
    <input type="submit" name="SaveStuff" value="Save" />
    <input type="submit" name="ExportStuff" value="Export" />
</form>

In my controller i have a class that handles multiple submit buttons and depending on the button name it would redirect to a method. below is the SaveStuff method

    [HttpPost]
    [SubmitButtonClass(Name = "SaveStuff")]
    public ActionResult Save_Definition(Owner owner, Tenant tnt) 
    {
        /*
          Stuff Here
        */
    }

the problem here is i keep getting null values even thought the entities are not null. is there a reason why? no values are returned.

Update
Model A

 public partial class Owner
{
    public long ID { get; set; }
    public bool is_Checked_Name { get; set; }
    public bool is_Checked_Phone { get; set; }
}

Model B

 public partial class Tenant
{
    public long ID{ get; set; }
    public bool is_Checked_Name { get; set; }
    public bool is_Checked_Adress { get; set; }
}

these are auto generated using EF

Answer 1

You have multiple issues with your code. Firstly the model in your view is ModelView and you generating form controls prefixed with that models property names, for example

<input type="checkbox" name="owner.is_Checked_Phone" ... />

which means your POST method needs to match the model in the view

public ActionResult Save_Definition(ModelView model)

The next issue is that you model only has fields, not properties with { get; set; }, so the DefaultModelBinder cannot set any values. Your view model would need properties such as public Owner owner { get; set; } and you set the value in either the controller before you pass the model to the view, or in a parameterless constructor for ModelView.

However a view model should not contain properties which are data models, but rather be a flat structure containing only the properties you need. In your case, it would be

public class ModelView
{
    public long ID { get; set; }
    [Display(Name = "Name")]
    public bool IsNameSelected { get; set; }
    [Display(Name = "Phone")]
    public bool IsPhoneSelected { get; set; }
    [Display(Name = "Address")]
    public bool IsAddressSelected { get; set; }
    // additional property to define if the form is for an Owner or Tenant
    public bool IsOwner { get; set; }
}

and in the GET method

var model = new ModelView()
{
    IsOwner = true // or false
};
return View(model);

and in the view

@model ModelView
....
@using (Html.BeginForm("Save_Definition"))
{
    @Html.HiddenFor(m => m.ID)
    @Html.HiddenFor(m => m.IsOwner)
    @Html.CheckBoxFor(m => m.IsNameSelected )
    @Html.LabelFor(m => m.IsNameSelected )
    if (Model.IsOwner)
    {
        @Html.CheckBoxFor(m => m.IsPhoneSelected)
        @Html.LabelFor(m => m.IsPhoneSelected)
    }
    else
    {
        @Html.CheckBoxFor(m => m.IsAddressSelected)
        @Html.LabelFor(m => m.IsAddressSelected)
    }
    .... // submit buttons
}

and the POST method, you can check the value of model.IsOwner to know if you have submitted an Owner or Tenant and take the appropriate action.

Side notes:

1. Recommend you read What is ViewModel in MVC?
2. The <table> element is for tabular data. Do not use it for layout.
3. Your view has <form action="Export" .. > yet your POST method is named Save_Definition so unsure which method you intending to submit the form to.

Answer 2

If your post controller is changing original model data, you will need to issue a ModelState.Remove("propertyname") followed by model.propertyname = "new value" and then a simple return View(model) will update the changed value on your already posted view.