MVC DropDownList滞后 [英] MVC DropDownList lagging
问题描述
我正在将下拉列表的ID发回到索引(index2视图).但落后了.再按一次Select(选择)按钮，它会向我显示正确的列表.
http://www.jeroenchristens.be/CountriesWorld (第一页仅用于显示完整列表，从下拉列表中进行选择后，它会进入index2(一个较短的列表).然后从下拉列表中选择另一个选择"后，您每次必须尝试两次.
我成功地从id中复制了该值并将其传递给它，为什么它滞后了.
Index2 Viewpage
@using System.Collections
@using System.Web.UI.WebControls
@model IEnumerable<CVtje.Models.Countries>
<h2>Index</h2>
@using (Html.BeginForm("Index2", "CountriesWorld", new { @id = Request.Form["SelectedContinent"] }, FormMethod.Post))
{
<div class="form-group">
@Html.DropDownList("SelectedContinent",
new SelectList((IEnumerable) ViewData["continentsList"], "Continent", "Continentomschrijving"))
<button type="submit" class="btn btn-primary">Select</button>
</div>
}
<table id="countriesworld" class="table table-active table-hover">
<thead>
<tr>
<th>Vlag</th>
<th>
Code
</th>
<th>
Land
</th>
<th>Continent</th>
</tr>
</thead>
@foreach (var item in Model)
{
<tr>
<td>
<img src="@string.Format("../../images/countries/{0}.png", item.Code)" width="25" HEIGHT="15" />
</td>
<td>
@item.Code
</td>
<td>
@item.Country
@*@Html.ActionLink("Details", "Index", "ReizensDetails", new { id = item.ReizenId }, null)*@
@*|
@Html.ActionLink("Details", "Details", new { id = item.Id }) |
<button data-myprofile-id="@item.Id" class="btn-link js-delete">Delete</button>*@
</td>
<td>@item.Continents.Continentomschrijving</td>
</tr>
}
</table>
我的控制器:
public ActionResult Index(int? id)
{
List<Continents> continentsList = new List<Continents>();
continentsList = _context.Continents.ToList();
ViewData["continentsList"] = continentsList;
var countriesWorld = _context.Countries.OrderBy(e => e.Country).ToList();
return View(countriesWorld);
}
[HttpPost]
public ActionResult Index2(int id)
{
//return View(db.MyProfiles.ToList());
List<Continents> continentsList = new List<Continents>();
continentsList = _context.Continents.ToList();
ViewData["SelectedContinent"] = id.ToString();
ViewData["continentsList"] = continentsList;
var countriesWorld = _context.Countries.Where(e => e.Continent == id).OrderBy(e => e.Country).ToList();
return View(countriesWorld);
您已经在BeginForm()方法中使用new { @id = Request.Form["SelectedContinent"] }添加了路由值.
假设初始值为0，则它将生成action = "/CountriesWorld/Index2/0".假设您使用value="1"选择选项，然后发布表单. id属性绑定到0，并且您基于.Where(e => e.Continent == 0)过滤国家/地区-在哪里都没有使用所选选项的值绑定到一个不存在的名为SelectedContinent的属性. >
现在，您返回视图，并且表单action的属性现在为action = "/CountriesWorld/Index2/1"(因为Request.Form["SelectedContinent"]为1).如果使用value="2"选择选项，则会发生相同的事情-您忽略所选选项的值，并过滤基于.Where(e => e.Continent == 1)的国家/地区，因为id参数是1.
始终绑定到一个模型，在您的情况下将是
public class CountriesVM
{
public int? SelectedContinent { get; set }
public IEnumerable<SelectListItem> ContinentsList { get; set; }
public IEnumerable<Country> Countries { get; set; }
}
并在视图中牢固绑定到模型(请注意FormMethod.Get和DropDownListFor()中的第3个参数)
@model CountriesVM
@using (Html.BeginForm("Index", "CountriesWorld", FormMethod.Get))
{
@Html.DropDownListFor(m => m.SelectedContinent, Model.ContinentsList, "All")
<button type="submit" class="btn btn-primary">Select</button>
}
<table ... >
....
@foreach(var country in Model.Countries)
{
....
}
</table>
您只需要一种方法
public ActionResult Index(int? selectedContinent)
{
var countries = _context.Countries.OrderBy(e => e.Country);
if (selectedContinent.HasValue)
{
countries = countries.Where(e => e.Continent == selectedContinent.Value);
}
continentsList = _context.Continents.Select(x => new SelectListItem
{
Value = x.Continent.ToString(),
Text = x.Continentomschrijving
});
var model = new CountriesVM
{
SelectedContinent = selectedContinent,
ContinentsList = continentsList,
Countries = countries
};
return View(model);
}
请注意，您可能还想考虑缓存Continents，以防止重复的数据库调用(假设它们不经常更改)(并且如果更新其值，则使缓存无效)
I am posting the id of a dropdownlist back to the index (index2 view). but is lagging behind. After a second time pressing Select it shows me the correct list.
http://www.jeroenchristens.be/CountriesWorld (the first page is only for showing the complete list, after selecting from the dropdownlist,, it gets to index2, a shorter list) And then after choosing another Selection from the dropdownlist, you have to try this twice each time.
I successfully copied this from the id the value and pass this on, why is it lagging behind.
Index2 Viewpage
@using System.Collections
@using System.Web.UI.WebControls
@model IEnumerable<CVtje.Models.Countries>
<h2>Index</h2>
@using (Html.BeginForm("Index2", "CountriesWorld", new { @id = Request.Form["SelectedContinent"] }, FormMethod.Post))
{
<div class="form-group">
@Html.DropDownList("SelectedContinent",
new SelectList((IEnumerable) ViewData["continentsList"], "Continent", "Continentomschrijving"))
<button type="submit" class="btn btn-primary">Select</button>
</div>
}
<table id="countriesworld" class="table table-active table-hover">
<thead>
<tr>
<th>Vlag</th>
<th>
Code
</th>
<th>
Land
</th>
<th>Continent</th>
</tr>
</thead>
@foreach (var item in Model)
{
<tr>
<td>
<img src="@string.Format("../../images/countries/{0}.png", item.Code)" width="25" HEIGHT="15" />
</td>
<td>
@item.Code
</td>
<td>
@item.Country
@*@Html.ActionLink("Details", "Index", "ReizensDetails", new { id = item.ReizenId }, null)*@
@*|
@Html.ActionLink("Details", "Details", new { id = item.Id }) |
<button data-myprofile-id="@item.Id" class="btn-link js-delete">Delete</button>*@
</td>
<td>@item.Continents.Continentomschrijving</td>
</tr>
}
</table>
my controller:
public ActionResult Index(int? id)
{
List<Continents> continentsList = new List<Continents>();
continentsList = _context.Continents.ToList();
ViewData["continentsList"] = continentsList;
var countriesWorld = _context.Countries.OrderBy(e => e.Country).ToList();
return View(countriesWorld);
}
[HttpPost]
public ActionResult Index2(int id)
{
//return View(db.MyProfiles.ToList());
List<Continents> continentsList = new List<Continents>();
continentsList = _context.Continents.ToList();
ViewData["SelectedContinent"] = id.ToString();
ViewData["continentsList"] = continentsList;
var countriesWorld = _context.Countries.Where(e => e.Continent == id).OrderBy(e => e.Country).ToList();
return View(countriesWorld);
You have added a route value using new { @id = Request.Form["SelectedContinent"] } in your BeginForm() method.
Assuming the initial value is 0, then it generates action = "/CountriesWorld/Index2/0". Lets assume you select the option with value="1" and you now post the form. The id attribute is bound to 0 and you filter the Countries based on .Where(e => e.Continent == 0) - no where have you ever used the value of the selected option which is bound to a non-existent property named SelectedContinent.
Now you return the view and the forms action attribute is now action = "/CountriesWorld/Index2/1" (because Request.Form["SelectedContinent"] is 1). If you select the option with value="2", the same thing occurs - you ignore the value of the selected option and the filter the Countries based on .Where(e => e.Continent == 1) because the id parameter is 1.
Always bind to a model, which in your case will be
public class CountriesVM
{
public int? SelectedContinent { get; set }
public IEnumerable<SelectListItem> ContinentsList { get; set; }
public IEnumerable<Country> Countries { get; set; }
}
and in the view, strongly bind to your model (note the FormMethod.Get and the 3rd parameter in DropDownListFor())
@model CountriesVM
@using (Html.BeginForm("Index", "CountriesWorld", FormMethod.Get))
{
@Html.DropDownListFor(m => m.SelectedContinent, Model.ContinentsList, "All")
<button type="submit" class="btn btn-primary">Select</button>
}
<table ... >
....
@foreach(var country in Model.Countries)
{
....
}
</table>
and you need only one method
public ActionResult Index(int? selectedContinent)
{
var countries = _context.Countries.OrderBy(e => e.Country);
if (selectedContinent.HasValue)
{
countries = countries.Where(e => e.Continent == selectedContinent.Value);
}
continentsList = _context.Continents.Select(x => new SelectListItem
{
Value = x.Continent.ToString(),
Text = x.Continentomschrijving
});
var model = new CountriesVM
{
SelectedContinent = selectedContinent,
ContinentsList = continentsList,
Countries = countries
};
return View(model);
}
Note you might also want to consider caching the Continents to avoid repeated database calls assuming they do not change often (and invalidate the cache if their values are updated)
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