ASP.NET MVC ViewModel属性为null

Question

I have the following ViewModel:

public class ProjectViewModel
{
    public Project Project { get; set; }
    public Customer Customer { get; set; }
}

The Customer property is only used to link a new Project to the Customer, so I don't include this property in my Create view, which looks like this:

@using (Html.BeginForm()) 
{
@Html.AntiForgeryToken()

<div class="form-horizontal">
    <h4>Project</h4>
    <hr />
    @Html.ValidationSummary(true, "", new { @class = "text-danger" })
    <div class="form-group">
        @Html.LabelFor(model => model.Project.Name, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.Project.Name, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.Project.Name, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" value="Create" class="btn btn-default" />
        </div>
    </div>
</div>
}

When I post the form, the following method in my ProjectsController is triggered:

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create([Bind(Include = "Project,Customer")] ProjectViewModel vm)
{
    var project = Mapper.Map<Project>(vm);
    if (ModelState.IsValid)
    {
        _db.Create(project);
        return RedirectToAction("Index");
    }
    return View(vm);
}

This is where the unexpected behaviour occurs. Now, when I examine the vm property, the Customer property is null .

The question How can I still keep the Customer property filled, while not using it in the view?

Answer 1

如果要保留客户数据，则需要将所有字段设置为隐藏元素，否则它们将在重定向中丢失。

@Html.HiddenFor(model => model.Customer.Property1) ...etc...

Answer 2

The short answer is that you can't. When data is posted back, the only data that is included is what is in the form on the HTML page.

Your best bet is to either use a session variable or look up the data again in the post handler, or alternatively, serialize the data to hidden fields.

Answer 3

To make sure the Customer property is never null when initializing ProjectViewModel , you could add a constructor to your ProjectViewModel class initializing the Customer property to a new Customer() like so:

public class ProjectViewModel
{
    // Constructor
    public ProjectViewModel()
    {
        Customer = new Customer();
    }

    public Customer Customer { get; set; }
}