ModelBinded IList项为空OnPost

Question

在我的页面中，基于这样的模型生成多个表单：

@for (var i = 0; i < Model.CaseData.Case.CaseSheets.Count; i++)
{
    Model.CaseData.CaseSheetNum = i;
    <div class="sheet @Model.CaseData.Case.CaseSheets[i].Id hide">
        <form method="post">
            <input type="hidden" asp-for="CaseData.Case.Id" />
            <input type="hidden" asp-for="CaseData.Case.CaseSheets[i].Id" />
            <input type="hidden" asp-for="CaseData.CaseSheetNum" />
            <h2>@Model.CaseData.Case.CaseSheets[i].Title</h2>
            @for (var n = 0; n < Model.CaseData.Case.CaseSheets[i].CaseSheetOptions.Count; n++)
            {
                Model.CaseData.CaseSheetOptionNum = n;
                await Html.RenderPartialAsync("PartialName", Model.CaseData);
            }
            <br /><p class="text-right"><button type="submit" name="Submit" class="btn">Save sheet</button></p>
        </form>
    </div>
}

发布表单时，我可以获取CaseData.Case.Id的值，但CaseData.Case.CaseSheets为空（应为6个项目的列表）。

模型：

public class Case
{

    public Guid Id { get; set; }
    public Guid AccountId { get; set; }
    public DateTime CreatedDate { get; set; }
    public Guid CreatedBy { get; set; }
    public DateTime? ClosedDate { get; set; }
    public Guid? ClosedBy { get; set; }
    public int Status { get; set; }

    public IList<CaseSheet> CaseSheets { get; set; }

}

public class CaseSheet
{

    public Guid Id { get; set; }
    public string Title { get; set; }
    public int MajorNum { get; set; }
    public int MinorNum { get; set; }
    public Guid CaseId { get; set; }
    public int Status { get; set; }

    public IList<CaseSheetOption> CaseSheetOptions { get; set; }

}

public class CaseSheetOption
{

    public Guid Id { get; set; }
    public string Headline { get; set; }
    public string Text { get; set; }
    public bool Yes { get; set; }
    public bool No { get; set; }
    public string Comment { get; set; }
    public Guid CaseSheetId { get; set; }
    public int Priority { get; set; }
    public int Status { get; set; }

}

public class CaseData
{

    public Case Case { get; set; }
    public int CaseSheetNum { get; set; }
    public int CaseSheetOptionNum { get; set; }

}

控制器：

[BindProperty]
public CaseData CaseData { get; set; }

public async Task<IActionResult> OnGetAsync(Guid id)
{

    var c = await _dbContext.Cases.Include(x => x.CaseSheets).ThenInclude(x => x.CaseSheetOptions).FirstOrDefaultAsync(x => x.Id == id);
    c.CaseSheets = c.CaseSheets.OrderBy(x => x.MajorNum).ThenBy(x => x.MinorNum).ToList();

    foreach (var sheet in c.CaseSheets)
    {
        sheet.CaseSheetOptions = sheet.CaseSheetOptions.OrderBy(x => x.Priority).ToList();
    }

    CaseData = new CaseData
    {
        Case = c,
        CaseSheetNum = 0,
        CaseSheetOptionNum = 0
    };

    return Page();

}

public async Task<IActionResult> OnPostAsync()
{

    var caseSheets = CaseData.Case.CaseSheets;
    int caseSheetNum = CaseData.CaseSheetNum;
    Guid caseSheetId = caseSheets[caseSheetNum].Id;         

    var sheetOptions = await _dbContext.CaseSheetOptions.Where(x => x.CaseSheetId == caseSheetId && x.Status == 1).ToListAsync();

    foreach (var option in caseSheets[caseSheetNum].CaseSheetOptions)
    {
        var sheetOption = sheetOptions.FirstOrDefault(x => x.Id == option.Id);
        sheetOption.Yes = option.Yes;
        sheetOption.No = option.No;
        sheetOption.Comment = option.Comment;
        _dbContext.Update(sheetOption);
    }
    await _dbContext.SaveChangesAsync();

    return RedirectToPage("", new { caseSheetId });

}

在OnPost()中，caseSheets.GetType()是Generic.List，但是caseSheets.Count是0（应该是6）。

输入字段的命名类似于CaseData.Case.CaseSheets[2].CaseSheetOptions[0].Id。

我想念什么？