asp.net-mvc-4 - 在 ASP.NET MVC 4 中填充和选择下拉列表值

Question

ASP.NET MVC 中的下拉列表让我感到困惑。我有一个模型课。模型类有一个名为 SelectedValue 的字符串。此字符串表示先前选择的值。我有一组从数据库中提取的项目。集合的每个项目都有一个 ID 和一个 Name 值。我的问题是，我不知道将这些信息导入 UI 的推荐方法是什么。

我不确定我应该使用 ViewBag 还是 Model。但是，一旦值在那里，我什至不确定填充 UI 的最佳方式是什么。我见过 HTML 助手和使用 RAZOR 语法的人。我很困惑。人们推荐什么？

谢谢

Answer 1

我就是这样做的，假设你有 2 个模型Team and Player：

播放器.cs

public class Player
{
    [HiddenInput(DisplayValue = false)]
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }        

    [Required]
    [ForeignKey("Team")]
    [Display(Name = "Team")]
    public int TeamId { get; set; }        

    [Display(Name = "First name")]
    public string FirstName { get; set; }

    [Display(Name = "Last name")]
    public string LastName { get; set; }

    public virtual Team Team { get; set; }        
}

团队.cs

 public class Team
{
    [Key]
    [HiddenInput(DisplayValue = false)]
    public int TeamId { get; set; }

    [Display(Name = "Full Name:")]
    public string Name { get; set; }        

    public virtual ICollection<Player> Players { get; set; }
}

然后在你的 PlayerController 中： 注意：团队需要存在才能创建一个玩家

    private void PopulateTeamsDropDownList(object selectedTeams = null)
    {
        var teamsQuery = from d in _dataSource.Teams
                         orderby d.Name
                         select d;
        ViewBag.TeamID = new SelectList(teamsQuery, "TeamId", "Name", selectedTeams);
    }

    [HttpGet]
    public ActionResult Create()
    {
        PopulateTeamsDropDownList();
        return View();
    }

    [HttpPost]
    public ActionResult Create(Player model)
    {
        if (ModelState.IsValid)
        {
            using (EFootballDb db = new EFootballDb())
            {
                try
                {
                    var player = new Player
                                     {
                                         FirstName = model.FirstName,
                                         LastName = model.LastName
                                     };
                    db.Players.Add(player);
                    db.SaveChanges();
                    return RedirectToAction("About", "Home");
                }
                catch (Exception)
                {
                    ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
                }
            }
        }
        PopulateTeamsDropDownList(model.TeamId);
        return View(model);
    }

最后，您的 Create View for Player 将如下所示：

@{
ViewBag.Title = "Create";
 }

<h2>Create</h2>

@using (Html.BeginForm()) {
@Html.ValidationSummary(true)

<fieldset>
    <legend>Player</legend>

    <div class="editor-label">
            @Html.LabelFor(model => model.TeamId, "Pick Your Team")
    </div>
    <div class="editor-field">
        @Html.DropDownList("TeamId", String.Empty)
        @Html.ValidationMessageFor(model => model.TeamId)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.FirstName)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.FirstName)
        @Html.ValidationMessageFor(model => model.FirstName)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.LastName)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.LastName)
        @Html.ValidationMessageFor(model => model.LastName)
    </div>        

    <p>
        <input type="submit" value="Create" />
    </p>
  </fieldset>
 }

 <div>
     @Html.ActionLink("Back to List", "Index")
 </div>

 @section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

Answer 2

我这样做的方式是让下拉列表成为我的 ViewModel 的一部分 .... 说它是 Products .... 所以在我的 ViewModel 中我有一个

public SelectList Products { get; set;}
public int ProductId { get; set; }  // For the the selected Product

因此，当视图加载时，我正在填充模型以返回控制器中的视图，我会执行以下操作：

model.Products = new SelectList(MyEnumerableofProducts, "ValueField", "TextField", {value of the selected item in the dropdown, as a string)

在我看来，我会：

@Html.DropDownListFor(model => model.ProductId, Model.Products, "Please Select")



return View(model)

Answer 3

除了上述方法，您还可以使用此方法在查找表中使用多个外键。据我所见，它非常清晰有效。

Answer 4

如果您使用的是 VB.Net - MVC4- Razor 这个答案与 Frigik 几乎相同（感谢 Frigik）

在您的模型中创建两个字段，一个是保存 SelectedItem 的字段（这里是字符串的 TagType），第二个是下拉值（TagTypeList）

模型类- Tag.vb

Imports System.Web.Mvc

Private _tagType As String
Private _tagTypeList As List(Of SelectListItem)

Public Property TagType() As String
        Get
            Return _tagType
        End Get
        Set(ByVal value As String)
            _tagType = value
        End Set
End Property

Public Property TagTypeList() As List(Of SelectListItem)
        Get
            Return _tagTypeList
        End Get
        Set(value As List(Of SelectListItem))
            _tagTypeList = value
        End Set
    End Property

'In the constructor

Sub New()
        TagTypeList = CommonUtility.LoadDropDownByName("TAGTYPE")
End Sub

在 CommonUtility 类中 - CommonUtility.vb

Imports System.Web.Mvc
Imports System.Collections.Generic


Public Shared Function LoadDropDownByName(ByVal DropDownName As String) As List(Of SelectListItem)
        Dim dt As DataTable
        Dim ds As DataSet
        Dim results As List(Of SelectListItem) = Nothing
        Try
            ds = objSignOn.LoadDropDown(DropDownName)   'Pass the dropdown name here and get the values from DB table which is - select ddlId, ddlDesc from <table name>
            If Not ds Is Nothing Then
                dt = ds.Tables(0)
                If (dt.Rows.Count > 0) Then
                    results = (From p In dt Select New SelectListItem With {.Text = p.Item("ddlDesc").ToString(), .Value = p.Item("ddlId").ToString()}).ToList()
                End If
            End If
        Catch ex As Exception
        End Try
        Return results
    End Function

在视图中

@Html.DropDownListFor(Function(x) x.TagType, Model.TagTypeList, "", New With {.id = "ddlTagType",.class = "dropDown", .style = "width: 140px"})

这里第三个参数（可选）为空，它将在下拉列表中插入第一个为空的项目。第一个参数是 selectedItem，一旦值已经存在于 DB 表中，它有助于填充。

希望这对使用 VB.Net 的人有所帮助