asp.net-mvc 如何将项目添加到 ASP.net MVC 中的 SelectList
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How can I add an item to a SelectList in ASP.net MVC
提问by tvanfosson
Basically I am looking to insert an item at the beginning of a SelectList with the default value of 0 and the Text Value of " -- Select One --"
基本上，我希望在 SelectList 的开头插入一个项目，默认值为 0，文本值为“ -- Select One --”
Something like
就像是
SelectList list = new SelectList(repository.func.ToList());
ListItem li = new ListItem(value, value);
list.items.add(li);
Can this be done?
这能做到吗？
回答by tvanfosson
There really isn't a need to do this unless you insist on the value of 0. The HtmlHelper DropDownList extension allows you to set an option label that shows up as the initial value in the select with a null value. Simply use one of the DropDownList signatures that has the option label.
除非您坚持值为 0，否则确实没有必要这样做。 HtmlHelper DropDownList 扩展允许您设置一个选项标签，该标签在选择中显示为带有空值的初始值。只需使用具有选项标签的 DropDownList 签名之一。
<%= Html.DropDownList( "DropDownValue",
(IEnumerable<SelectListItem>)ViewData["Menu"],
"-- Select One --" ) %>
回答by davewilliams459
I got this to work by Populating a SelectListItem, converting to an List, and adding a value at index 0.
我通过填充 SelectListItem、转换为 List 并在索引 0 处添加值来实现此目的。
List<SelectListItem> items = new SelectList(CurrentViewSetups, "SetupId", "SetupName", setupid).ToList();
items.Insert(0, (new SelectListItem { Text = "[None]", Value = "0" }));
ViewData["SetupsSelectList"] = items;
回答by eaf
This is possible.
这个有可能。
//Create the select list item you want to add
SelectListItem selListItem = new SelectListItem() { Value = "null", Text = "Select One" };
//Create a list of select list items - this will be returned as your select list
List<SelectListItem> newList = new List<SelectListItem>();
//Add select list item to list of selectlistitems
newList.Add(selListItem);
//Return the list of selectlistitems as a selectlist
return new SelectList(newList, "Value", "Text", null);
回答by H Dog
I liked @AshOoO's answer but like @Rajan Rawal I needed to preserve selected item state, if any. So I added my customization to his method AddFirstItem()
我喜欢@AshOoO 的回答，但像@Rajan Rawal 一样，我需要保留所选项目的状态（如果有）。所以我在他的方法中添加了我的自定义AddFirstItem()
public static SelectList AddFirstItem(SelectList origList, SelectListItem firstItem)
{
List<SelectListItem> newList = origList.ToList();
newList.Insert(0, firstItem);
var selectedItem = newList.FirstOrDefault(item => item.Selected);
var selectedItemValue = String.Empty;
if (selectedItem != null)
{
selectedItemValue = selectedItem.Value;
}
return new SelectList(newList, "Value", "Text", selectedItemValue);
}
回答by hidden
Here html helper for you
这里有 html 帮手
public static SelectList IndividualNamesOrAll(this SelectList Object)
{
MedicalVarianceViewsDataContext LinqCtx = new MedicalVarianceViewsDataContext();
//not correct need individual view!
var IndividualsListBoxRaw = ( from x in LinqCtx.ViewIndividualsNames
orderby x.FullName
select x);
List<SelectListItem> items = new SelectList (
IndividualsListBoxRaw,
"First_Hospital_Case_Nbr",
"FullName"
).ToList();
items.Insert(0, (new SelectListItem { Text = "All Individuals",
Value = "0.0",
Selected = true }));
Object = new SelectList (items,"Value","Text");
return Object;
}
回答by AshOoO
private SelectList AddFirstItem(SelectList list)
{
List<SelectListItem> _list = list.ToList();
_list.Insert(0, new SelectListItem() { Value = "-1", Text = "This Is First Item" });
return new SelectList((IEnumerable<SelectListItem>)_list, "Value", "Text");
}
This Should do what you need ,just send your selectlist and it will return a select list with an item in index 0
这应该做你需要的，只需发送你的选择列表，它就会返回一个索引为 0 的项目的选择列表
You can custome the text,value or even the index of the item you need to insert
您可以自定义需要插入的项目的文本、值甚至索引
回答by Moji
The .ToList().Insert(..)method puts an element into your List. Any position can be specified. After ToList just add .Insert(0, "- - First Item - -")
该.ToList（）。插入（..）方法放一个元素到你的列表中。可以指定任何位置。在 ToList 之后添加.Insert(0, "- - First Item - -")
Your code
你的代码
SelectList list = new SelectList(repository.func.ToList());
ListItem li = new ListItem(value, value);
list.items.add(li);
New Code
新代码
SelectList list = new SelectList(repository.func.ToList().Insert(0, "- - First Item - -"));
ListItem li = new ListItem(value, value);
list.items.add(li);
回答by Androiderson
May not sound very elegant, but I usually do something like this:
听起来可能不太优雅，但我通常会这样做：
var items = repository.func.ToList();
items.Insert(0, new funcItem { ID = 0, TextValue = "[None]" });
ViewBag.MyData = new SelectList(items);
回答by Jeff
Okay I like clean code so I made this an extension method
好吧，我喜欢干净的代码，所以我把它变成了一个扩展方法
static public class SelectListHelper
{
static public SelectList Add(this SelectList list, string text, string value = "", ListPosition listPosition = ListPosition.First)
{
if (string.IsNullOrEmpty(value))
{
value = text;
}
var listItems = list.ToList();
var lp = (int)listPosition;
switch (lp)
{
case -1:
lp = list.Count();
break;
case -2:
lp = list.Count() / 2;
break;
case -3:
var random = new Random();
lp = random.Next(0, list.Count());
break;
}
listItems.Insert(lp, new SelectListItem { Value = value, Text = text });
list = new SelectList(listItems, "Value", "Text");
return list;
}
public enum ListPosition
{
First = 0,
Last = -1,
Middle = -2,
Random = -3
}
}
Usage (by example):
用法（举例）：
var model = new VmRoutePicker
{
Routes =
new SelectList(_dataSource.Routes.Select(r => r.RouteID).Distinct())
};
model.Routes = model.Routes.Add("All", "All", SelectListHelper.ListPosition.Random);
//or
model.Routes = model.Routes.Add("All");
回答by sairfan
As this option may need in many different manners, i reached to conclusion to develop an object so that it can be used in different scenarios and in future projects
由于此选项可能需要以多种不同的方式，因此我得出结论开发一个对象，以便它可以在不同的场景和未来的项目中使用
first add this class to your project
首先将此类添加到您的项目中
public class SelectListDefaults
{
private IList<SelectListItem> getDefaultItems = new List<SelectListItem>();
public SelectListDefaults()
{
this.AddDefaultItem("(All)", "-1");
}
public SelectListDefaults(string text, string value)
{
this.AddDefaultItem(text, value);
}
public IList<SelectListItem> GetDefaultItems
{
get
{
return getDefaultItems;
}
}
public void AddDefaultItem(string text, string value)
{
getDefaultItems.Add(new SelectListItem() { Text = text, Value = value });
}
}
Now in Controller Action you can do like this
现在在控制器操作中你可以这样做
// Now you can do like this
ViewBag.MainCategories = new SelectListDefaults().GetDefaultItems.Concat(new SelectList(db.MainCategories, "MainCategoryID", "Name", Request["DropDownListMainCategory"] ?? "-1"));
// Or can change it by such a simple way
ViewBag.MainCategories = new SelectListDefaults("Any","0").GetDefaultItems.Concat(new SelectList(db.MainCategories, "MainCategoryID", "Name", Request["DropDownListMainCategory"] ?? "0"));
// And even can add more options
SelectListDefaults listDefaults = new SelectListDefaults();
listDefaults.AddDefaultItme("(Top 5)", "-5");
// If Top 5 selected by user, you may need to do something here with db.MainCategories, or pass in parameter to method
ViewBag.MainCategories = listDefaults.GetDefaultItems.Concat(new SelectList(db.MainCategories, "MainCategoryID", "Name", Request["DropDownListMainCategory"] ?? "-1"));
And finally in View you will code like this.
最后在 View 中，您将像这样编码。
@Html.DropDownList("DropDownListMainCategory", (IEnumerable<SelectListItem>)ViewBag.MainCategories, new { @class = "form-control", onchange = "this.form.submit();" })
