TextBox不显示值（MVC4）

Question

我在视图中有以下控件：

<div class="editor-label">
@Html.LabelFor(model => model.Number)
</div>
<div class="editor-field">
@Html.HiddenFor(model => model.Number)
@Html.TextBoxFor(model => model.Number, new { disabled = "disabled" })
</div>
<div class="editor-label">
@Html.LabelFor(model => model.ProjectID)
</div>
<div class="editor-field">
@Html.DropDownListFor(model => model.Project.ID, Model.ProjectList, "Select", new { onchange = "SelectedIndexChanged()" })
</div>

我在下拉列表值更改时提交表单以生成模型的Number字段，然后重新加载视图。如果没有HiddenFor控件，则在TextBoxFor中正确显示模型的编号。当我添加HiddenFor控件时，虽然Model.Number不为null，但不会显示Number字段。

这是什么原因？

我想要一个带有Number值的HiddenFor的原因是当我提交表单进行保存时，model.Number等于null。我想通过将值放在HiddenFor中我可以访问它...

编辑：控制器方法

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult CreateOpportunity(CreateEditOpportunityModel model)
    {
        // if the submit is made by the ddl
        if (model.SubmitValue.Equals("ChangeProject"))
        {
            Project parentProject = pCtx.Projects.Find(model.Project.ID);

            if (parentProject != null)
            {   
                // Generate the "Number field"
                Region projectRegion = rCtx.Regions.Find(parentProject.RegionID);
                int numOpportunity = oCtx.Opportunitites.Count(o => o.ProjectID == parentProject.ID);
                numOpportunity++;
                string oppNumber = numOpportunity < 10 ? "0" + numOpportunity : numOpportunity.ToString();
                model.Number = projectRegion.Name + "-" + parentProject.ID + "-" + oppNumber;



            }

            // Repopulate the ddl
            model.ProjectList = new SelectList(pCtx.Projects, "ID", "ID");

            return View(model);
        }

        // if submit is made by the save button
        else if (model.SubmitValue.Equals("CreateOpportunity"))
        {
            if (ModelState.IsValid)
            {
                Opportunity opportunity = new Opportunity();
                opportunity.ID = model.ID;
                opportunity.Number = model.Number;
                opportunity.ActivationDate = model.ActivationDate;
                opportunity.Assignee = model.Assignee;
                opportunity.Comments = model.Comments;
                opportunity.CreationDate = DateTime.Now;
                opportunity.LicenseFilePath = model.LicenseFilePath;
                opportunity.LicenseRequestFilePath = model.LicenseRequestFilePath;
                opportunity.OkPermanentStatus = model.OkPermanentStatus;
                opportunity.PaidStatus = model.PaidStatus;
                opportunity.PartNumber = model.PartNumber;
                opportunity.Project = pCtx.Projects.Find(model.Project.ID);

                //tell EF that Project already exists in Company table
                oCtx.Entry(opportunity.Project).State = EntityState.Modified;

                // Saves project
                oCtx.Opportunitites.Add(opportunity);
                oCtx.SaveChanges();
                return RedirectToAction("Index");
            }

            model.ProjectList = new SelectList(pCtx.Projects, "ID", "ID");

            return View(model);
        }

        model.ProjectList = new SelectList(pCtx.Projects, "ID", "ID");

        return View(model);
    }

这部分代码运行正常，我只是把它放在这里澄清事情。