默认模型绑定抛出“没有为此对象定义无参数构造函数”

我有一个表格，我们想在其中为单个客户输入多个交易。表单的视图模型如下所示：

public class TradeSpendingEntryViewModel
{
    public TradeSpendingEntryViewModel()
    {
        Records = new List<TradeSpendingEntryViewModelRecord>();
    }

    public string CustomerNumber { get; set; }
    public DateTime Date { get; set; }
    public SelectList PlanningYears { get; set; }

    public List<TradeSpendingEntryViewModelRecord> Records { get; set; }
}

我们希望能够使用 JavaScript 动态添加和删除记录条目行。集合中的每条记录是：

public class TradeSpendingEntryViewModelRecord
{
    public TradeSpendingEntryViewModelRecord()
    {
    }

    public string LOB { get; set; }
    public string ProductCode { get; set; }
    public SelectList AllowType { get; set; }
    public int Cases { get; set; }
    public bool EndCurrentDeal { get; set; }
    public Single DealRate { get; set; }
    public DateTime StartDate { get; set; }
    public DateTime EndDate { get; set; }
    public string Comments { get; set; }
}

当我尝试将数据发布到控制器时，出现错误，指示“没有为此对象定义无参数构造函数：

[HttpPost]
    public ActionResult Index(TradeSpendingEntryViewModel vm)
    {
        try
        {
            if (ModelState.IsValid)
            {
                return RedirectToAction("Index");
            }
            // TODO: Add insert logic here
            return View(vm);
        }
        catch
        {
            return View();
        }
    }

堆栈跟踪表明它发生在模型绑定期间：

[MissingMethodException：没有为此对象定义无参数构造函数。] System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0 System.RuntimeType.CreateInstanceSlow（布尔publicOnly，布尔skipCheckThis，布尔fillCache，StackCrawlMark＆stackMark）+113 System.RuntimeType.CreateInstanceDefaultCtor（布尔publicOnly，布尔skipCheckThis，布尔fillCache，StackCrawlMark＆stackMark）+232 System.Activator.CreateInstance（类型类型，布尔非公共）+83 System.Activator.CreateInstance(类型类型) +6 System.Web.Mvc.DefaultModelBinder.CreateModel（ControllerContextcontrollerContext，ModelBindingContext绑定Context，类型modelType）+183

我的问题一定源于我如何设置视图，其标记是基于本文的http://www.hanselman.com/blog/ASPNETWireFormatForModelBindingToArraysListsCollectionsDictionaries.aspx http://www.hanselman.com/blog/ASPNETWireFormatForModelBindingToArraysListsCollectionsDictionaries.aspx

@using (Html.BeginForm())
{
<header class="clearfix">
        <img src="../../Content/images/logo.png" alt="Irving Consumer Products" />
        <h1>Enter Customer Deals</h1>
    </header>
    <hr />
    <fieldset>
        <legend>Customer details</legend>
        <table>
            <tr>
                <th>
                    Date:
                </th>
                <td>
                    <input type="date" disabled="disabled" value="@DateTime.Today.ToShortDateString()" />
            </tr>
            <tr>
                <th>
                    Customer Number:
                </th>
                <td>
                    @Html.TextBoxFor(m => m.CustomerNumber, new { id = "customer-number" })
                    <a href="#" id="change-customer-number">Change me</a>
                </td>
            </tr>
            <tr>
                <th>
                    Customer Name:
                </th>
                <td>
                    <input type="text" id="customer-name" disabled="disabled" />
                </td>
                <tr>
                    <th>
                        Planning Year:
                    </th>
                    <td>
                        @Html.DropDownList("PlanningYear", Model.PlanningYears)
                        <a href="#" id="change-planning-year">Change me</a>
                    </td>
                </tr>
        </table>
    </fieldset>
    <div class="buttonGroup">
        <input type="button" value="Add line" id="add-line">
        <input type="button" value="Copy line" id="copy-line">
        <input type="button" value="Delete line" id="delete-line">
    </div>
    <hr />
    <table id="tradeSpendingEntry">
        <thead>
            <tr>
                <th>
                </th>
                <th>
                    Line of business
                </th>
                <th>
                    Product Code
                </th>
                <th>
                    Product Description
                </th>
                <th>
                    Allowance
                    <br />
                    Type
                </th>
                <th>
                    Cases
                </th>
                <th>
                    End Current Deal
                </th>
                <th>
                    Start Date
                </th>
                <th>
                    End Date
                </th>
                <th>
                    Rate
                </th>
            </tr>
        </thead>
        @foreach (var r in Model.Records)
        {
            <tbody data-entry-index="0">
            <tr>
                <td>
                    <input type="checkbox" />
                </td>
                <td>
                    <input type="text" name="records[0].LOB" class="lobSelect" value="@r.LOB">
                </td>
                <td>
                    <!--<input type="hidden" name="records[0]ProductCodeSelected" value="@r.ProductCode" />-->
                    <input type="text" name="records[0].ProductCode" value="@r.ProductCode">
                </td>
                <td>
                    <input type="text" class="product-description" disabled="disabled" />
                </td>
                <td>
                    @Html.DropDownList("records[0].AllowType", r.AllowType)
                </td>
                <td>
                    <input name="records[0].Cases" type="number" />
                </td>
                <td>
                    <select name="records[0].EndCurrentDeal">
                        <option value="true" selected="selected">Yes</option>
                        <option value="false">No</option>
                    </select>
                </td>
                <td>
                    <input type="date" name="records[0].StartDate" />
                </td>
                <td>
                    <input type="date" name="records[0].EndDate" />
                </td>
                <td>
                    <input type="text" name="records[0].DealRate" />
                </td>
                </tr>
            <tr>
                <td></td>
                <td>
                    Comments:
                </td>
                <td colspan="8">
                    <input type="text" class="comment" name="records[0].Comments" />
                </td>
                </tr>
        </tbody>
        }
    </table>

    <footer>
        <div class="buttonGroup">
        <input type="submit" value="Submit Changes">
        <input type="button" value="Main Menu">
        <input type="button" value="View Customer Deals">
    </div>
    </footer>
    }

因此，我希望第一个字段集中的字段能够映射到 TradeSpendingEntryViewModel 对象的直接属性（CustomerName、Date、PlanningYears）。然后，对于每个代表 TradeSpendingEntryViewModelRecord 的对象，将被绑定为 TradeSpendingEntryViewModel.Records 集合中的一项。相反，我只是得到一个神秘的“未定义无参数构造函数”异常，尽管 ViewModel 和记录对象都具有无参数构造函数。

我的问题是，我可以使用上述文章中指出的约定使用默认模型绑定程序，还是需要为此目的构建自定义模型绑定程序？

为了完整起见，以下是用户通过 javascript 向表单动态添加一行后生成的表单标记：

<form method="post" action="/TradeSpendingEntry/Index">
<header class="clearfix">
<img alt="Irving Consumer Products" src="../../Content/images/logo.png">
<h1>Enter Customer Deals</h1>
</header>
<hr>
<fieldset>
<legend>Customer details</legend>
<table>
<tbody>
<tr>
<th> Date: </th>
<td>
<input id="dp1363608756704" class="hasDatepicker" type="date" value="18/03/2013" disabled="disabled" style="background-color: rgb(238, 238, 238);">
</td>
</tr>
<tr>
<th> Customer Number: </th>
<td>
<input id="customer-number" type="text" value="" name="CustomerNumber">
<a id="change-customer-number" href="#">Change me</a>
</td>
</tr>
<tr>
<th> Customer Name: </th>
<td>
<input id="customer-name" type="text" disabled="disabled" style="background-color: rgb(238, 238, 238);">
</td>
</tr>
<tr>
<th> Planning Year: </th>
<td>
<select id="PlanningYears" name="PlanningYears">
<option value="2011">2011</option>
<option value="2012">2012</option>
<option value="2013">2013</option>
<option value="2014">2014</option>
</select>
<a id="change-planning-year" href="#">Change me</a>
</td>
</tr>
</tbody>
</table>
</fieldset>
<div class="buttonGroup">
<input id="add-line" type="button" value="Add line">
<input id="copy-line" type="button" value="Copy line">
<input id="delete-line" type="button" value="Delete line">
</div>
<hr>
<table id="tradeSpendingEntry">
<thead>
<tr>
<th> </th>
<th> Line of business </th>
<th> Product Code </th>
<th> Product Description </th>
<th>
Allowance
<br>
Type
</th>
<th> Cases </th>
<th> End Current Deal </th>
<th> Start Date </th>
<th> End Date </th>
<th> Rate </th>
</tr>
</thead>
<tbody data-entry-index="0">
<tr>
<td>
<input type="checkbox">
</td>
<td>
<input class="lobSelect" type="text" name="records[0].LOB">
</td>
<td>
<input type="text" name="records[0].ProductCode">
</td>
<td>
<input class="product-description" type="text" disabled="disabled" style="background-color: rgb(238, 238, 238);">
</td>
<td>
<select id="records_0__AllowType" name="records[0].AllowType">
<option selected="selected">BillBack$</option>
<option>Billback%</option>
<option>O&A%</option>
<option>Coop%</option>
<option>VR%</option>
<option>Lump - O&A$</option>
<option>Lump - CP$</option>
<option>Lump - VR$</option>
<option>Lump - BB$</option>
</select>
</td>
<td>
<input type="number" name="records[0].Cases">
</td>
<td>
<select name="records[0].EndCurrentDeal">
<option selected="selected" value="true">Yes</option>
<option value="false">No</option>
</select>
</td>
<td>
<input id="dp1363608756707" class="hasDatepicker" type="date" name="records[0].StartDate">
</td>
<td>
<input id="dp1363608756708" class="hasDatepicker" type="date" name="records[0].EndDate">
</td>
<td>
<input type="text" name="records[0].DealRate">
</td>
</tr>
<tr>
<td></td>
<td> Comments: </td>
<td colspan="8">
<input class="comment" type="text" name="records[0].Comments">
</td>
</tr>
</tbody>
<tbody data-entry-index="1">
<tr>
<td>
<input type="checkbox">
</td>
<td>
<input class="lobSelect" type="text" name="records[1].LOB">
</td>
<td>
<input type="text" name="records[1].ProductCode">
</td>
<td>
<input class="product-description" type="text" disabled="disabled" style="background-color: rgb(238, 238, 238);">
</td>
<td>
<select id="records_0__AllowType" name="records[1].AllowType">
<option selected="selected">BillBack$</option>
<option>Billback%</option>
<option>O&A%</option>
<option>Coop%</option>
<option>VR%</option>
<option>Lump - O&A$</option>
<option>Lump - CP$</option>
<option>Lump - VR$</option>
<option>Lump - BB$</option>
</select>
</td>
<td>
<input type="number" name="records[1].Cases">
</td>
<td>
<select name="records[1].EndCurrentDeal">
<option selected="selected" value="true">Yes</option>
<option value="false">No</option>
</select>
</td>
<td>
<input id="dp1363608756709" class="hasDatepicker" type="date" name="records[1].StartDate">
</td>
<td>
<input id="dp1363608756710" class="hasDatepicker" type="date" name="records[1].EndDate">
</td>
<td>
<input type="text" name="records[1].DealRate">
</td>
</tr>
<tr>
<td></td>
<td> Comments: </td>
<td colspan="8">
<input class="comment" type="text" name="records[1].Comments">
</td>
</tr>
</tbody>
</table>
<footer>
<div class="buttonGroup">
<input type="submit" value="Submit Changes">
<input type="button" value="Main Menu">
<input type="button" value="View Customer Deals">
</div>
</footer>
</form>

毫无疑问它就是SelectList。就在昨天我也遇到了同样的问题。

如果您查看 SelectList，它的所有构造函数都需要一个参数。http://msdn.microsoft.com/en-us/library/system.web.mvc.selectlist(v=vs.108).aspx http://msdn.microsoft.com/en-us/library/system.web.mvc.selectlist(v=vs.108).aspx

问题是当你的Action叫做public ActionResult Index(TradeSpendingEntryViewModel vm)

控制器尝试绑定发回的数据POST to TradeSpendingEntryViewModel需要根据其设置值PlanningYears它厌倦了通过创建一个新的SelectList

要解决此问题，您需要将 SelectList 设置为私有变量（也称为支持字段），然后默认将其设置为空列表。这为其提供了所需的参数化构造函数：

    //select list
    private SelectList planningYears = new SelectList(new List<YourObject>());

    public SelectList PlanningYears 
    {
        get
        {
            return planningYears;
        }
        set
        {
            locations = planningYears;
        }
    }

或者将 PlanningYears 更改为 List 并将其转换为视图上的选择列表。

@Html.DropDownListFor(m => m.PlanningYears , new SelectList(Model.PlanningYears ), "choose", null)