具有 IEnumerable 或 List 字段的 ASP.NET Core MVC 发布模型为空答案

【问题标题】：ASP.NET Core MVC post model with IEnumerable or List fields are null具有 IEnumerable 或 List 字段的 ASP.NET Core MVC 发布模型为空
【发布时间】：2021-02-27 21:27:16
【问题描述】：

我需要帮助来找出下一个错误。我正在尝试使用列表参数发布模型。但是，当我收到列表时，它的值为空。

模型类：

public class DiagModel{
    public List<Component> components { get; set; }
    public List<Question> questions { get; set; }
    public List<Answer> answers { get; set; }
    public List<Questionnaire> forms { get; set; } //it populates after instatiate object from the questions 
    //forms->(The propierties are idQuestion and idAnswer)
}

视图如下所示（省略了 fors 中对象的每个属性的@Html.hiddenFor()）：

@using Test.Models.compounds;
@model DiagModel;

@{
    Layout = "~/Views/Shared/_LayoutCommon.cshtml";
}

@if (!string.IsNullOrEmpty(ViewBag.Message))
{
    <script type="text/javascript">
        alert("@ViewBag.Message");
    </script>
}

@using (Html.BeginForm(new { @id = "requestForm" }))
{
    @for (int i = 0; i < Model.components.Count(); i++)
    {
        //The hidden components with razor helper was deleted to make short the code [Component]        
        <div class="row text-center">
            <div class="col-md-10 offset-md-1 text-start" style="background-color: #dddddd">
                <span class="text-start">@Model.components[i].name</span>
            </div>
        </div>
        <div class="row">&nbsp;</div>
        
        List<Question> _questions = Model.questions.Where(p => p.Idcomponent == Model.components[i].Idcomponent).ToList();
        for (int j = 0; j < _questions.Count; j++)
        {
            //The hidden components with razor helper was deleted to make short the code [Question]
            <div class="row p-1">
                <div class="col-md-10 offset-md-1 text-start">
                    <label class="form-label fw-bold">@_questions[j].Idquestion @_questions[j].Textopregunta</label>
                    @Html.DropDownListFor(model => model.forms.Where(c => c.Idquestion == @_questions[j].Idquestion).First().Idanswer, new SelectList(Model.answers.Where(r => r.Idquestion == @_questions.ElementAt(j).Idquestion), "Idquestion", "Text"), "Select an option", new { @class = "form-control" })
                </div>
            </div>
            <div class="row">&nbsp;</div>
            }


    }
    <div class="row p-1 text-center">
        <div class="col-md-12">
            <button name="submit" type="submit" class="btn btn-danger" formaction="Question" value=@Model>Enviar</button>
        </div><!--end col -->
    </div>


}
<div class="row p-2">&nbsp;</div>

控制器获取值但集合被接收为空。

[HttpPost]
public ActionResult Question(DiagModel model){
    //ViewBag.Message($"Q #1: {model.forms.First().IdQuestion} , R #1: {model.forms.First().IdAnswer}"); 
    ViewBag.Message = $"count: {model.forms.Count}";//Breakpoint
    if (ModelState.IsValid) {
        return View(model);
    }
    return View("Index");
}

【问题讨论】：

标签： c# html

【解决方案1】：

你只能发送带有表单的input元素，或者您可以使用 javascript xhr 请求将它们作为参数发送。

razor 最重要的是输入元素 [name] 属性需要匹配模型字段。

<input type="text" name="questions[1].Id" class="form-label fw-bold" value="@Model.questions[1].Id" />

如果您处理嵌套对象，则它必须反映在您尝试在服务器端绑定的模型上。

【讨论】：