C# 下拉选择未被清除
我试图从下拉列表中清除所选的值,但该值仍然存在。使用C# 下拉选择未被清除,c#,asp.net-mvc,asp.net-core-mvc,C#,Asp.net Mvc,Asp.net Core Mvc,我试图从下拉列表中清除所选的值,但该值仍然存在。使用@Html.DropDownListFor 控制器 public class HomeController : Controller { [Route("/Home/Index")] [Route("/Home/Index/{Category}")] [Route("/Home/Index/{Category}/{Type}")] public IActionResult Index(HomeModel mod
@Html.DropDownListFor
控制器
public class HomeController : Controller
{
[Route("/Home/Index")]
[Route("/Home/Index/{Category}")]
[Route("/Home/Index/{Category}/{Type}")]
public IActionResult Index(HomeModel model)
{
// Issue is here
// for url: home/index/accessories/test
// "Category" is cleared if it is not valid "type"
// but still "Accessories" remains selected in the drop down
if (model.Type != "Electronics" && model.Type != "Furniture")
{
model.Category = string.Empty;
}
return View(new HomeModel() { Category = model.Category, Type = model.Type });
}
查看
@model WebApplication1.Controllers.HomeModel
<select asp-for="Category" asp-items="@Model.Categories"></select>
<select asp-for="Type" asp-items="@Model.Types"></select>
@model WebApplication1.Controllers.HomeModel
型号
public class HomeModel
{
public string Category { get; set; }
public string Type { get; set; }
public List<SelectListItem> Categories { get; set; } = new List<SelectListItem>
{
new SelectListItem() { Text="Computers & Laptops", Value="Computers-Laptops" },
new SelectListItem() { Text="Accessories", Value="Accessories" },
};
public List<SelectListItem> Types { get; set; } = new List<SelectListItem>
{
new SelectListItem() { Text="Electronics", Value="Electronics" },
new SelectListItem() { Text="Furniture", Value="Furniture" },
};
}
公共类HomeModel
{
公共字符串类别{get;set;}
公共字符串类型{get;set;}
公共列表类别{get;set;}=新列表
{
新建SelectListItem(){Text=“Computers&Laptops”,Value=“Computers Laptops”},
新建SelectListItem(){Text=“附件”,Value=“附件”},
};
公共列表类型{get;set;}=新列表
{
新建SelectListItem(){Text=“Electronics”,Value=“Electronics”},
新建SelectListItem(){Text=“Furniture”,Value=“Furniture”},
};
}
更新
我试图在类别下拉列表中添加一个空值,但仍然没有成功
<select asp-for="Category" asp-items="@Model.Categories">
<option value="">Select Category</option>
</select>
选择类别
问题在ModelState
中。当URL参数绑定到视图模型时,会将这些值添加到模型状态字典中。渲染视图时,不仅会将HomeModel
传递给视图,而且还会在场景下方传递ModelState
,并且该视图的属性高于视图模型。因此,当您重置model.Category
时,ModelState
中的Category
键仍然具有值附件
,这就是为什么在下拉列表中选择它
解决方案很简单,请调用.Clear()
清除模型状态并使视图模型获胜:
[Route("/Home/Index")]
[Route("/Home/Index/{Category}")]
[Route("/Home/Index/{Category}/{Type}")]
public IActionResult Index(HomeModel model) {
// Issue is here
// for url: home/index/accessories/test
// "Category" is cleared if it is not valid "type"
// but still "Accessories" remains selected in the drop down
if (model.Type != "Electronics" && model.Type != "Furniture") {
model.Category = string.Empty;
}
ModelState.Clear();
return View(new HomeModel() { Category = model.Category, Type = model.Type });
}
问题在
ModelState
中。当URL参数绑定到视图模型时,会将这些值添加到模型状态字典中。渲染视图时,不仅会将HomeModel
传递给视图,而且还会在场景下方传递ModelState
,并且该视图的属性高于视图模型。因此,当您重置model.Category
时,ModelState
中的Category
键仍然具有值附件
,这就是为什么在下拉列表中选择它
解决方案很简单,请调用.Clear()
清除模型状态并使视图模型获胜:
[Route("/Home/Index")]
[Route("/Home/Index/{Category}")]
[Route("/Home/Index/{Category}/{Type}")]
public IActionResult Index(HomeModel model) {
// Issue is here
// for url: home/index/accessories/test
// "Category" is cleared if it is not valid "type"
// but still "Accessories" remains selected in the drop down
if (model.Type != "Electronics" && model.Type != "Furniture") {
model.Category = string.Empty;
}
ModelState.Clear();
return View(new HomeModel() { Category = model.Category, Type = model.Type });
}
选择列表中没有空值。尝试添加Text=”“选项。@KevinRaffay在添加空值后,它仍然不工作。我猜,它正在从路由中拾取值。浏览器中生成了什么html?发生错误时,您是否向该方法发布或发布了任何内容?或者只是访问“新鲜”链接?选择列表中没有空值。尝试添加Text=”“选项。@KevinRaffay在添加空值后,它仍然不工作。我猜,它正在从路由中拾取值。浏览器中生成了什么html?发生错误时,您是否向该方法发布或发布了任何内容?或者只是访问一个“新鲜”链接?