列表<SelectListItem>未顯示 @Html.DropDownListFor 的選定值

Question

我有一個剃須刀頁面。 在加載時，它會通過以下函數並創建一個 SelectListItem 列表：

        List<SelectListItem> groups = new List<SelectListItem>();
        for (int i = 0; i < Model.List.key.Count(); i++)
        {
            bool selected = false;
            if(Model.List.key[i] == Model.rkey)
            {
                selected = true;
            }
            groups.Add(new SelectListItem
            {
                Text = Model.List.description[i],
                Value = Model.List.key[i].ToString(),
                Selected = selected
            });
        }

當鍵匹配時，它正確地將 Selected 值設置為 true，但是它沒有顯示所選值：

@Html.DropDownListFor(model => Model.groupTypeList, groups, new { @class = "form-control", onchange = "chosenGroup(this.value)", id = "groupTypeList" })

上面的 ddl 顯示了所有添加的值，但沒有設置為 Selected 值。 我嘗試了以下但它然后顯示選定的值兩次：

@Html.DropDownListFor(model => Model.groupTypeList, groups, groups.First(x => x.Selected == true).Text, new { @class = "form-control", onchange = "chosenGroup(this.value)", id = "groupTypeList" })

Answer 1

你可以試試這個：

模型：

public class Group
{
    public IEnumerable<Key> List { get; set; }

    public int rkey { get; set; }
}

public class Key
{
    public int key { get; set; }

    public string desc { get; set; }
}

動作控制器：

public ActionResult Index()
{
    Group g = new Group
    { 
        List = new List<Key>() 
        { 
            new Key { key = 1, desc = "Test" } ,
            new Key { key = 2, desc = "Test2" },
            new Key { key = 3, desc = "Test3" },
            new Key { key = 4, desc = "Test4" },
            new Key { key = 5, desc = "Test5" }
        } 
    };

    g.rkey = 4;

    return View(g);
}

看法：

@model WebMVC.Models.Group

<div> 

    @{

        List<SelectListItem> groups = new List<SelectListItem>();

        for (int i = 0; i < Model.List.Count(); i++)
        {
            bool selected = false;

            if (Model.List.ElementAt(i).key == Model.rkey)
            {
                selected = true;
            }

            groups.Add(new SelectListItem {  Text = Model.List.ElementAt(i).desc, Value = Model.List.ElementAt(i).key.ToString(), Selected = selected });
        }

    }

    <label>Select option:</label>

    @Html.DropDownList("MyDropDownList", groups, null, new { @class = "form-control", onchange = "chosenGroup(this.value)", id = "groupTypeList" })

</div>

另一種方法是直接使用DropdownListFor而不在視圖中進行 razor 驗證：

@Html.DropDownListFor(x => x.rkey, new SelectList(Model.List, "key", "desc"), null, new { @class = "form-control", onchange = "chosenGroup(this.value)", id = "groupTypeList" })