无法将下拉列表中的选定项设置为控制器

本文关键字：设置 控制器 下拉列表 | 更新日期: 2023-09-27 17:50:52

在我看来下拉列表显示了正确的字段，但是当我在"编辑或创建"中选择一个字段时，该字段将被保存/修改为NULL。在调试时，我可以看到新值没有发送。我认为ID和SurveyID不匹配…

视图:

@model Project_ASP_2012.Models.QuestionGroup
@{
ViewBag.Title = "Edit";
}
<h2>Edit</h2>
@using (Html.BeginForm()) {
@Html.ValidationSummary(true)
<fieldset>
    <legend>QuestionGroup</legend>
    @Html.HiddenFor(model => model.ID)

    <div class="editor-label">
        @Html.LabelFor(model => model.Description)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.Description)
        @Html.ValidationMessageFor(model => model.Description)
    </div>
    <div class="editor-label">
        @Html.LabelFor(model => model.SurveyID, "Survey")
    </div>
    <div class="editor-field">
        @Html.DropDownList("Id", String.Empty)
        @Html.ValidationMessageFor(model => model.SurveyID)
    </div>
    <p>
        <input type="submit" value="Save" />
    </p>
</fieldset>
}
<div>
@Html.ActionLink("Back to List", "Index")
</div>
 @section Scripts {
@Scripts.Render("~/bundles/jqueryval")
}

模型:

public class Survey : IEntity
{

    [Key]
    [Display(Name = "SurveyID")]
    public int ID { get; set; }
    [Required(ErrorMessage = "Survey title is required.")]
    [Display(Name = "Survey Title")]
    [MaxLength(20, ErrorMessage = "Title cannot be longer than 20 characters.")]
    public string Title { get; set; }
    [MaxLength(50, ErrorMessage = "Description cannot be longer than 50 characters.")]
    public string Description { get; set; }
    public virtual ICollection<QuestionGroup> QuestionGroups { get; set; }
}
public class QuestionGroup : IEntity
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ID { get; set; }
    [MaxLength(50, ErrorMessage = "Description cannot be longer than 50 characters.")]
    public string Description { get; set; }
    [Display(Name = "SurveyID")]
    public int? SurveyID { get; set; }
    public virtual Survey Survey { get; set; }
}

控制器:

    public ActionResult Edit(int id)
    {
        QuestionGroup questiongroup = unitOfWork.QuestionGroupRepository.GetById(id);
        if (questiongroup == null)
        {
            return HttpNotFound();
        }
        PopulateSurveysDropDownList(questiongroup.SurveyID);
        return View(questiongroup);
    }
    //
    // POST: /QuestionGroup/Edit/5
    [HttpPost]
    public ActionResult Edit(QuestionGroup questiongroup)
    {
        try
        {
           if (ModelState.IsValid)
            {
                unitOfWork.UoWContext.Entry(questiongroup).State = EntityState.Modified;
                unitOfWork.SaveChanges();
                return RedirectToAction("Index");
            }
        }
        catch (DataException)
        {
            ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists see your system administrator.");
        }
        PopulateSurveysDropDownList(questiongroup.SurveyID);
        return View(questiongroup);
    }

    private void PopulateSurveysDropDownList(object selectedSurvey = null)
    {
        var surveyQuery = unitOfWork.SurveyRepository.Get(
            orderBy: q => q.OrderBy(d => d.Title));
        ViewBag.Id = new SelectList(surveyQuery, "Id", "Title", selectedSurvey);
    }

无法将下拉列表中的选定项设置为控制器

在您的视图中，您有Id下拉而不是SurveyId。此外，您还可以在下拉框和隐藏字段中设置两次ID。

<div class="editor-field">
    @Html.DropDownList("Id", String.Empty)
    @Html.ValidationMessageFor(model => model.SurveyID)
</div>

尝试更改:

private void PopulateSurveysDropDownList(object selectedSurvey = null)
{
    var surveyQuery = unitOfWork.SurveyRepository.Get(
        orderBy: q => q.OrderBy(d => d.Title));
    ViewBag.Id = new SelectList(surveyQuery, "Id", "Title", selectedSurvey);
}
....
<div class="editor-field">
    @Html.DropDownList("Id", String.Empty)
    @Html.ValidationMessageFor(model => model.SurveyID)
</div>

: 

private void PopulateSurveysDropDownList(object selectedSurvey = null)
{
    var surveyQuery = unitOfWork.SurveyRepository.Get(
        orderBy: q => q.OrderBy(d => d.Title));
    //don't provide the select value here.  you will bind to it in your view
    ViewBag.SurveySelectList = new SelectList(surveyQuery, "Id", "Title");
}
....
<div class="editor-field">
    //selected value will be whatever SurveyID is on your model.
    @Html.DropDownListFor(model => model.SurveyID, ViewBag.SurveySelectList, String.Empty)
    @Html.ValidationMessageFor(model => model.SurveyID)
</div>

希望对你有帮助。

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