我需要在表单内张贴对象列表，它包含另一个列表，但我得到了这个错误：

索引超出范围。必须为非负数且小于集合的大小

我的模型：

public class SurveyQuestionDto
{
    public SurveyQuestionDto()
    {
        SurveyChoices = new List<SurveyChoiceDto>();
    }

    public int SurveyQuesId { get; set; }

    public DateTime? DateStart { get; set; }

    public DateTime? DateEnd { get; set; }

    [Required(ErrorMessage = "Required")]
    public short ChoicesType { get; set; }

    [StringLength(500, ErrorMessage = "MaxLength")]
    public string TextAnswer { get; set; }

    public virtual List<SurveyChoiceDto> SurveyChoices { get; set; }
}

public class SurveyChoiceDto
{

    [Required(ErrorMessage = "Required")]
    public int? LanguageId { get; set; }

    [Required(ErrorMessage = "Required"),
    StringLength(200, ErrorMessage = "MaxLength")]
    public string Title { get; set; }

    public long ChoiceId { get; set; }

    public int SurveyQuesId { get; set; }

    public long Count { get; set; }

    public bool MarkedToDelete { get; set; }

    public bool IsSelected { get; set; }
}

我的看法是：

@model List<SurveyQuestionDto>

@if (Model != null && Model.Count() > 0)
{
    <form action="@Url.Action("Answer", "Survey", new { typeId })" method="post" class="form form-horizontal" enctype="multipart/form-data">
        @Html.AntiForgeryToken()
        @Html.ValidationSummary(true)

        @foreach (var question in Model)
        {
            int i = 0;
            @Html.HiddenFor(m => m[i].SurveyQuesId, new { Value = question.SurveyQuesId })
            <div style="background:#cccccc; padding:20px; margin:20px;">
                <h2>@question.Title</h2>
                @if (question.ChoicesType == (int)ChoicesTypeEnum.Text)
                {
                    @Html.TextAreaFor(m => m[i].TextAnswer, new Dictionary<string, object> { { "data-val", "true" }, { "data-val-required", _loc["Required"] } })
                }
                else
                {
                    <ul style="list-style-type:none;">
                        @foreach (var choice in question.SurveyChoices)
                        {
                            int a = 0;
                            <li>
                                @Html.HiddenFor(m => m[i].SurveyChoices[a].ChoiceId, new { Value = choice.ChoiceId })
                                @if (question.ChoicesType == (int)ChoicesTypeEnum.SingleChoice)
                                {
                                    @Html.RadioButtonFor(m => m[i].SurveyChoices[a].IsSelected, null, new Dictionary<string, object> { { "data-val", "true" }, { "data-val-required", _loc["Required"] } })
                                }
                                else
                                {
                                    @Html.CheckBoxFor(m => m[i].SurveyChoices[a].IsSelected, new Dictionary<string, object> { { "data-val", "true" }, { "data-val-required", _loc["Required"] } })
                                }
                                <label>@choice.Title</label>
                            </li>
                            a++;
                        }
                    </ul>
                }
            </div>
            i++;
        }
        <button type="submit">Submit now</button>
    </form>
}

模型对象已经有了它的值：

public async Task<IActionResult> Index(int id)
{
    return View(await _rep.GetSurveyQuestionsWithChoices(id));
}

问题从这行代码m[i]开始。调查选择[a]。有什么建议吗？