如何获得MVC下拉选择值

Question

我正在一个MVC项目中，在其中对Employee对象执行CRUD（创建/读取/更新/删除）操作。

这是问题所在：我正在使用一个下拉列表将DepartmentName分配给该员工，并且在编辑该员工时，我想在较早分配给他的Department下拉列表中获取该员工的选定值。

这是代码：

主视图

<table class="table" id="Grid">
<tr>
    <th>
        @Html.DisplayNameFor(model => model.Name)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.GenderName)
    </th>
    <th>
        @Html.DisplayNameFor(model => model.DepartmentName)
    </th>
    <th></th>
</tr>

@foreach (var item in Model)
{
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.Name)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.GenderName)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.DepartmentName)
        </td>

        @if (Context.User.IsInRole("Admin"))
        {
            <td>
                @Html.ActionLink("Edit", "Edit", new { id = item.Id })

                @Html.ActionLink("Delete", "Delete", new { id = item.Id }, new { onclick = "return confirm('Are sure wants to delete?');" })
            </td>
        }
    </tr>
}

DBHelper

public List<Emloyee> GetEmployees()
{
    connection();
    List<Emloyee> employeelist = new List<Emloyee>();


    SqlCommand cmd = new SqlCommand("GetEmployeeDetails", con);
    cmd.CommandType = CommandType.StoredProcedure;
    SqlDataAdapter sd = new SqlDataAdapter(cmd);
    DataTable dt = new DataTable();


    con.Open();
    sd.Fill(dt);
    con.Close();

    foreach (DataRow dr in dt.Rows)
    {
        employeelist.Add(
            new Emloyee
            {
                Id = Convert.ToInt32(dr["Id"]),
                Name = Convert.ToString(dr["Name"]),
                GenderName = Convert.ToString(dr["GenderName"]),
                DepartmentName = Convert.ToString(dr["DepartmentName"])
            });
    }
    return employeelist;
}

调节器

public ActionResult Edit(int id)
{
    EmployeeDB edb = new EmployeeDB();
    var depart = edb.GetDepartment();
    ViewBag.DepartmentId = new SelectList(depart, "DepartmentId", "DepartmentName");


    return PartialView(edb.GetEmployees().Find(cmodel => cmodel.Id == id));
}

编辑视图

<div class="form-group">
    @Html.LabelFor(model => model.DepartmentName, htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownList("DepartmentId",(SelectList)ViewBag.DepartmentId, new { @class = "form-control" })

    </div>
</div>

Answer 1

如之前在注释中所述，您的Employee模型不包含departmentId ，在模型中包括departmentId 。 我怀疑这是您无法在“编辑视图”上查看部门的原因。 我相信下面的代码片段将解决此问题。

public List<Emloyee> GetEmployees()
{
    connection();
    List<Emloyee> employeelist = new List<Emloyee>();


    SqlCommand cmd = new SqlCommand("GetEmployeeDetails", con);
    cmd.CommandType = CommandType.StoredProcedure;
    SqlDataAdapter sd = new SqlDataAdapter(cmd);
    DataTable dt = new DataTable();


    con.Open();
    sd.Fill(dt);
    con.Close();

    foreach (DataRow dr in dt.Rows)
    {
        employeelist.Add(
            new Emloyee
            {
                Id = Convert.ToInt32(dr["Id"]),
                Name = Convert.ToString(dr["Name"]),
                GenderName = Convert.ToString(dr["GenderName"]),
                DepartmentName = Convert.ToString(dr["DepartmentName"])
                DepartmentId = Convert.ToInt32(dr["DepartmentId "])
            });
    }
    return employeelist;
}

控制器动作

public ActionResult Edit(int id)
{
    EmployeeDB edb = new EmployeeDB();
    var depart = edb.GetDepartment();
    ViewBag.Departments = new SelectList(depart, "DepartmentId", 
  "DepartmentName");


    return PartialView(edb.GetEmployees().Find(cmodel => cmodel.Id == id));
}

查看：

<div class="form-group">
    @Html.LabelFor(model => model.DepartmentName, htmlAttributes: new { @class = "control-label col-md-2" })
    <div class="col-md-10">
        @Html.DropDownList("DepartmentId",(SelectList)ViewBag.Departments, new { @class = "form-control" })

    </div>
</div>

Answer 2

您可以将构造函数设置为在selectList的默认值时覆盖第四个参数。

ViewBag.DepartmentId = new SelectList(depart, "DepartmentId", "DepartmentName",[setYourDefaultValue]);

的SelectList

编辑

您的DropDownList需要将SelectListItem设置为null

@Html.DropDownList("DepartmentId",null, new { @class = "form-control" })

您可以在asp.net MVC selectList上看到源代码

如果使用此覆盖方法。

DropDownList(HtmlHelper, String, IEnumerable<SelectListItem>, IDictionary<String, Object>)

您需要将selectList设置为null以获得默认值。

private static MvcHtmlString SelectInternal(this HtmlHelper htmlHelper, ModelMetadata metadata,
    string optionLabel, string name, IEnumerable<SelectListItem> selectList, bool allowMultiple,
    IDictionary<string, object> htmlAttributes)
{
    string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
    if (String.IsNullOrEmpty(fullName))
    {
        throw new ArgumentException(MvcResources.Common_NullOrEmpty, "name");
    }

    bool usedViewData = false;

    // If we got a null selectList, try to use ViewData to get the list of items.
    if (selectList == null)
    {
        selectList = htmlHelper.GetSelectData(name);
        usedViewData = true;
    }
    ....etc
}

MVCSourceCode