在 ASP.NET Core 中提交表单后如何保持选择的 SelectListItem 值？

Question

我正在尝试使用下拉列表过滤 table，但在 ASP.NET Core 中提交表单后我无法保持选中的 SelectListItem 值。

过滤器似乎有效，但每当页面重新加载时，所选项目始终相同

获取控制器

    public ActionResult Index(int myDropDown)
    {
        var myItems= new List<Items>();

        myItems = _myRepository.GetAllItems();

        var filteredItems = myItems.Where(x => x.Color.DemoId == myDropDown);
        
        if (myDropDown != 0 )
        {
            return View(filteredItems);
        }

        return View(myItems);
    }

Index.chtml

<form asp-controller="MyController">
<div class="row">
    <div class="form-group col-3">
        <select class="form-control" id="exampleFormControlSelect1" name="myDropDown" 
                asp-items="(_myRepository.GetDemos()).Select(x => new SelectListItem() 
                             { Text = x.Name, Value = x.Id.ToString()})" onchange="this.form.submit()">

        </select>
    </div>
 </form>

C# 方法

    public List<Demo> GetDemos()
    {
        var demos = _dbContext.Demos.Select(x => new Demo()
        {
            Id = x.Id,
            Name = x.Name
        }).ToList();

        return demos;
    }

Answer 1

trying to filter a table using a dropdown-list but I'm not able to keep SelectListItem value selected after submitting the form

您可以尝试动态设置 Selected 属性 of SelectListItem，如下所示。

<select class="form-control" id="exampleFormControlSelect1" name="myDropDown"
        asp-items="(_myRepository.GetDemos()).Select(x => new SelectListItem()
                    { Text = x.Name, Value = x.Id.ToString(), Selected = x.Id == ViewBag.SelectedIndex ? true : false })" onchange="this.form.submit()">
</select>

动作方法

public ActionResult Index(int myDropDown)
{
    var myItems = new List<Items>();

    myItems = _myRepository.GetAllItems();

    var filteredItems = myItems.Where(x => x.Color.DemoId == myDropDown);

    //pass selected value through ViewBag etc
    ViewBag.SelectedIndex = myDropDown;

    if (myDropDown != 0)
    {
        return View(filteredItems);
    }

    return View(myItems);
}

在 ASP.NET Core 中提交表单后如何保持选择的 SelectListItem 值？

How to keep SelectListItem value selected after submitting form in ASP.NET Core?

c#

asp.net-core

drop-down-menu

razor-pages

selectlistitem