回发表单时出错："Collection is read-only“

Question

我有一个5个字符串值的列表(每个问题的可能答案)，我想让用户键入。但是当我提交表单时，会出现一个错误："Collection is read-only“。这里出了什么问题？

这是我的视图模型：

public class QuestionVM
    {
        public QuestionVM() {
            PossibleAnswers = new string[5];
        }
        public QuestionVM(Question question) : this()
        {
            ID = question.ID;
            Text = question.Text;
            IsAssociatedWithProfessor = question.IsAssociatedWithProfessor;
            IsAssociatedWithAssistant = question.IsAssociatedWithAssistant;
        }
        public int? ID { get; set; }
        public string Text { get; set; }
        public bool IsAssociatedWithProfessor { get; set; }
        public bool IsAssociatedWithAssistant { get; set; }
        public IEnumerable<string> PossibleAnswers { get; set; }
        public Question ToQuestion(ApplicationDbContext context)
        {
            Question question = new Question
            {
                Text = this.Text,
                IsAssociatedWithProfessor = this.IsAssociatedWithProfessor,
                IsAssociatedWithAssistant = this.IsAssociatedWithAssistant
            };
            //ID will be null if creating new question
            if(ID != null)
            {
                question.ID = (int) ID;
            }
            foreach (string possibleAnswer in this.PossibleAnswersVM.PossibleAnswers)
            {
                if (!String.IsNullOrEmpty(possibleAnswer))
                {
                    PossibleAnswer existingPossibleAnswer = context.PossibleAnswers.SingleOrDefault(ans => ans.Text == possibleAnswer);
                    if (existingPossibleAnswer == null)
                    {
                        PossibleAnswer ans = new PossibleAnswer { Text = possibleAnswer };
                        context.PossibleAnswers.Add(ans);
                        question.PossibleAnswers.Add(ans);
                    }
                    else
                    {
                        question.PossibleAnswers.Add(existingPossibleAnswer);
                    }
                }
            }
            return question;
        }
    }

控制器中的我的post方法：

[HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult AddQuestion(QuestionVM questionVM)
        {
            try
            {
                if (ModelState.IsValid)
                {
                    Question question = questionVM.ToQuestion(context);
                    context.Questions.Add(question);
                    context.SaveChanges();
                    return RedirectToAction("Questions");
                }
            }
            catch (DataException /* dex */)
            {
                //Log the error (uncomment dex variable name and add a line here to write a log.
                ModelState.AddModelError("", "Trenutno nije moguće snimiti promjene, pokušajte ponovo.");
            }
            return View(questionVM);
        }

视图的一部分：

@Html.EditorFor(model => model.PossibleAnswers, "PossibleAnswers")

和模板：

@model IEnumerable<string>
@{
    ViewBag.Title = "PossibleAnswers";
}

@foreach (var str in Model)
{
       @Html.TextBoxFor(m => str)
}

Answer 1

请确保您遵循了以下提示：

1. 只需在Views/Shared/EditorTemplates文件夹内添加编辑器模板
2. 使用参数化模板通过定义适当的@models让应用程序检测起来更容易。《
3. 指南》在需要时使用[UIHint("TemplateName")]剃须刀。

看看aspnet-mvc-display-and-editor-templates吧。