How to get data from partial in form - asp.net-mvc

Question

I have
ASP.NET MVC Form in popup with some controls and partial (data grid) with his own Model.
here is popup:
<div id="AddEditDialog" class="none">
#using (Ajax.BeginForm("Save", "Templates", new AjaxOptions
{
InsertionMode = InsertionMode.Replace,
UpdateTargetId = "AddEditPlaceHolder",
OnSuccess = "OnSaveSuccess",
HttpMethod = "Post"
}))
{
<div>
<div id="AddEditPlaceHolder"></div>
<div id="PopupButtons" class="btn-holder-centered">
<input type="submit" value="Save" name="SaveButton" />
<input type="button" value="Cancel" name="SaveCancelButton" id="CancelEditHandler" />
</div>
</div>
}
</div>
here is form which I render in AddEditPlaceHolder via js:
#model TemplatesViewModel
<div class="form-field-plain overflow">
<div class="forRow narRow float-left">
#Html.LabelFor(x => x.Revocable)
#Html.CheckBoxFor(x => x.Revocable)
</div>
</div>
<div class="form-field-plain overflow">
<div class="forRow narRow float-left">
#Html.LabelFor(x => x.HtmlTemplate)
#Html.TextAreaFor(x => x.HtmlTemplate)
</div>
</div>
#Html.Partial("_VariablesGridView", Model.Variables)
_VariablesGridView.cshtml:
#model List<TemplateVariableViewModel>
<table id="TemplateVariablesGrid">
<thead>
<tr>
<td>Tag/Code</td>
<td>Prompt</td>
<td>Action</td>
</tr>
</thead>
<tbody>
#foreach (var i in Model)
{
<tr>
<td>
#Html.TextBox("txtTag", #i.Tag, new {})
</td>
<td>
#Html.TextBox("txtPrompt", #i.Prompt, new { })
</td>
<td>
#Html.HiddenFor(x => x.First(s => s.Id == #i.Id).Id)
<label class="delete-variable">delete</label>
</td>
</tr>
}
</tbody>
</table>
<br />
<input type="button" name="btnAddTemplateVariable" value="add new variable"/>
<br />
My problem is :
in Controller 'save form' method public ActionResult Save(TemplateViewModel model)
my model contains all data from form but TemplateViewModel.Variables is empty
Is there any way to fill it in there?
Models:
public class TemplateViewModel
{
public int Id { get; set; }
public string HtmlTemplate { get; set; }
public List<TemplateVariableViewModel> Variables { get; set; }
}
public class TemplateVariableViewModel
{
public int Id { get; set; }
public string Tag { get; set; }
public string Prompt { get; set; }
}

Answer 1

I believe it is because the ASP.Net MVC binding is not putting these fields in context, have a look at your field names delivered to the browser, what is txtTag prefixed by when it gets to the browser and what is is after you do the following:
#Html.Partial("_VariablesGridView", Model)
_VariablesGridView.cshtml:
#model TemplatesViewModel
...
#for (int i = 0; i < Model.Variables.Count; i++)
#Html.TextBox("txtTag", #Model.Variables[i].Tag, new {})
Forgive me if this fails miserably (again), I'm shooting from the hip.