Question

当表格最初显示时，我会显示问题和答案。我显示了多个单选按钮以供回答。因此用户只能选择一个答案。当我提交表单和操作方法调用时，会出现问题。我看到表单帖子然后答案模型变为空。因此，指导我如何编写代码，因为当表单发布时，答案模型不应为null。

这是完整的代码。请仔细阅读代码，如果需要更改答案模型将不会为空，此时表单将发布到操作方法。

我的ViewModels代码

namespace ViewModels
{
    public class Question
    {
        public int ID { set; get; }
        public string QuestionText { set; get; }

        public List<Answer> Answers { set; get; }
        [Required]
        public string SelectedAnswer { set; get; }

        public Question()
        {
            Answers = new List<Answer>();
        }
    }

    public class Answer
    {
        public int ID { set; get; }
        public string AnswerText { set; get; }
    }

    public class Evaluation
    {
        public List<Question> Questions { set; get; }
        public Evaluation()
        {
            Questions = new List<Question>();
        }
    }
}

controller code

 public ActionResult Index()
        {
            var evalVM = new Evaluation();

            //the below is hardcoded for DEMO. you may get the data from some  
            //other place and set the questions and answers

            var q1 = new Question { ID = 1, QuestionText = "What is your favourite language" };
            q1.Answers.Add(new Answer { ID = 12, AnswerText = "PHP" });
            q1.Answers.Add(new Answer { ID = 13, AnswerText = "ASP.NET" });
            q1.Answers.Add(new Answer { ID = 14, AnswerText = "Java" });
            evalVM.Questions.Add(q1);

            var q2 = new Question { ID = 2, QuestionText = "What is your favourite DB" };
            q2.Answers.Add(new Answer { ID = 16, AnswerText = "SQL Server" });
            q2.Answers.Add(new Answer { ID = 17, AnswerText = "MySQL" });
            q2.Answers.Add(new Answer { ID = 18, AnswerText = "Oracle" });
            evalVM.Questions.Add(q2);

            return View(evalVM);           
        }

 [HttpPost]
        public ActionResult Index(Evaluation model)
        {
            if (ModelState.IsValid)
            {
                foreach (var q in model.Questions)
                {
                    if(q.Answers==null)
                    {
                        // Answers is null
                    }
                    var qId = q.ID;
                    var selectedAnswer = q.SelectedAnswer;
                    // Save the data 

                }
                return RedirectToAction("ThankYou"); //PRG Pattern
            }
            //reload questions
            return View(model);
        }

index.cshtml code

@model ViewModels.Evaluation
<h2>Quiz 24</h2>
@using (Html.BeginForm())
{
    @Html.EditorFor(x=>x.Questions)
    <input type="submit" />
}

and view code which is stored in EditorTemplates folder

@model ViewModels.Question
<div>
    @Html.HiddenFor(x=>x.ID)
    <h3> @Model.QuestionText </h3>

    @foreach (var a in Model.Answers)
    {
        <p>
            @Html.RadioButtonFor(b=>b.SelectedAnswer,a.ID)  @a.AnswerText 
        </p>

    }
</div>

问题出在这里

 [HttpPost]
        public ActionResult Index(Evaluation model)
        {
            if (ModelState.IsValid)
            {
                foreach (var q in model.Questions)
                {
                    if(q.Answers==null)
                    {
                        // Answers is null
                    }
                    var qId = q.ID;
                    var selectedAnswer = q.SelectedAnswer;
                    // Save the data 

                }
                return RedirectToAction("ThankYou"); //PRG Pattern
            }
            //reload questions
            return View(model);
        }

q.Answers == null在我发布表单时变为null。我想知道如何在表单将发布到操作时以这种方式编写代码然后Answers应该为null。很多人告诉我，我需要手动重建模型，因为Answers将始终为null。 MVC中没有任何机制可以保留所有数据，并在发布表单时将其正确地反序列化为模型。

Answer 1

AnswerText通常我会建议为Editor Template模型使用另一个嵌套Answer，但在这种情况下，它会导致问题正确构建单选按钮组，并且aftwerwards将检索{{1}的值}}。作为一个简单的解决方案，我将通过以下方式调整SelectedAnswer Editor Template模型：

Question

这将创建以下HTML（跳过不相关的属性）：

<div>
    @Html.HiddenFor(x=>x.ID)
    <h3> @Model.QuestionText </h3>
    <div>
        @for (int i = 0; i < Model.Answers.Count; i++)
        {
            <p>
                @Html.RadioButtonFor(model => model.SelectedAnswer, Model.Answers[i].AnswerText  @Model.Answers[i].AnswerText
                @Html.HiddenFor(model => model.Answers[i].ID)
                @Html.HiddenFor(model => model.Answers[i].AnswerText)
            </p>
        }
    </div>
</div>

输出将允许MVC正确重建<input type="radio" name="Questions[0].SelectedAnswer" ...> <input type="hidden" name="Questions[0].Answers[0].ID" ...> <input type="hidden" name="Questions[0].Answers[0].AnswerText" ...>集合。

<强>更新

在原始代码中，您正在寻找Answer，因此我更新了代码，而不是Answer.AnswerText。

希望这有帮助。

如何在表单发布时保留模型数据

1 个答案: