blocks|key|1600132|text|除非您坚持将值设置为0，否则真的没有必要这样做。HtmlHelper+DropDownList扩展允许您设置一个选项标签，该标签在select中显示为具有空值的初始值。只需使用一个带有选项标签的DropDownList签名即可。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1600133|<%25=+Html.DropDownList(+"DropDownValue",
+++++++++++++++++++++++(IEnumerable<SelectListItem>)ViewData["Menu"],
++++++++++++++++++++++++"--+Select+One+--"+)+%25>|code-block|syntax|javascript|1600134|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

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.

<pre><code>&lt;%= Html.DropDownList( "DropDownValue",
 (IEnumerable&lt;SelectListItem&gt;)ViewData["Menu"],
 "-- Select One --" ) %&gt;
</code></pre>

blocks|key|1385376|text|我通过填充一个SelectListItem，转换为一个列表，并在索引0处添加一个值来实现这一点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1385377|List<SelectListItem>+items+=+new+SelectList(CurrentViewSetups,+"SetupId",+"SetupName",+setupid).ToList();+
items.Insert(0,+(new+SelectListItem+{+Text+=+"[None]",+Value+=+"0"+}));
ViewData["SetupsSelectList"]+=+items;|code-block|syntax|javascript|1385378|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I got this to work by Populating a SelectListItem, converting to an List, and adding a value at index 0. 

<pre><code>List&lt;SelectListItem&gt; items = new SelectList(CurrentViewSetups, "SetupId", "SetupName", setupid).ToList(); 
items.Insert(0, (new SelectListItem { Text = "[None]", Value = "0" }));
ViewData["SetupsSelectList"] = items;
</code></pre>

blocks|key|1600330|text|这是可能的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1600331|//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);|code-block|syntax|javascript|1600332|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is possible.

<pre><code>//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&lt;SelectListItem&gt; newList = new List&lt;SelectListItem&gt;();

//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);
</code></pre>

blocks|key|1600391|text|我喜欢@AshOoO的答案，但就像@Rajan+Rawal一样，我需要保留选定项的状态。因此，我将我的定制添加到他的方法AddFirstItem()中|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1600392|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);
}|code-block|syntax|javascript|1600393|entityMap^0|1O|E|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

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 <code>AddFirstItem()</code>

<pre><code>public static SelectList AddFirstItem(SelectList origList, SelectListItem firstItem)
{
 List&lt;SelectListItem&gt; newList = origList.ToList();
 newList.Insert(0, firstItem);

 var selectedItem = newList.FirstOrDefault(item =&gt; item.Selected);
 var selectedItemValue = String.Empty;
 if (selectedItem != null)
 {
 selectedItemValue = selectedItem.Value;
 }

 return new SelectList(newList, "Value", "Text", selectedItemValue);
}
</code></pre>

blocks|key|1385398|text|这里是为您准备的html+helper|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1385399|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;
}|code-block|syntax|javascript|1385400|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here html helper for you

<pre class="lang-cs prettyprint-override"><code>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&lt;SelectListItem&gt; 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;
}
</code></pre>

blocks|key|1600275|text|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");
++++++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1600276|这应该可以满足您的需求，只需发送您的选择列表，它将返回一个选择列表，其中包含索引0中的一项|unstyled|1600277|您可以保存需要插入的项目的文本、值甚至索引|1600278|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>private SelectList AddFirstItem(SelectList list)
 {
 List&lt;SelectListItem&gt; _list = list.ToList();
 _list.Insert(0, new SelectListItem() { Value = "-1", Text = "This Is First Item" });
 return new SelectList((IEnumerable&lt;SelectListItem&gt;)_list, "Value", "Text");
 }
</code></pre>

This Should do what you need ,just send your selectlist and it will return a select list with an item in index 0

You can custome the text,value or even the index of the item you need to insert

blocks|key|1385515|text|听起来可能不是很优雅，但我通常会这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1385516|++++var+items+=+repository.func.ToList();
++++items.Insert(0,+new+funcItem+{+ID+=+0,+TextValue+=+"[None]"+});
++++ViewBag.MyData+=+new+SelectList(items);|code-block|syntax|javascript|1385517|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

May not sound very elegant, but I usually do something like this:

<pre><code> var items = repository.func.ToList();
 items.Insert(0, new funcItem { ID = 0, TextValue = "[None]" });
 ViewBag.MyData = new SelectList(items);
</code></pre>

blocks|key|1385480|text|好的，我喜欢干净的代码，所以我把它作为一个扩展方法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1385481|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
++++}
}|code-block|syntax|javascript|1385482|用法(通过示例)：|1385483|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");|1385484|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Okay I like clean code so I made this an extension method

<pre><code>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
 }
}
</code></pre>

Usage (by example):

<pre><code>var model = new VmRoutePicker
 {
 Routes =
 new SelectList(_dataSource.Routes.Select(r =&gt; r.RouteID).Distinct())
 }; 
 model.Routes = model.Routes.Add("All", "All", SelectListHelper.ListPosition.Random);
//or
 model.Routes = model.Routes.Add("All");
</code></pre>

blocks|key|1600361|text|因为这个选项可能需要很多不同的方式，所以我得出结论来开发一个对象，以便它可以在不同的场景和未来的项目中使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1600362|首先，将此类添加到项目中|1600363|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+});++++++++++++++++++++
++++}
}|code-block|syntax|javascript|1600364|现在，在Controller+Action中，您可以这样做|1600365|++++//+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"));|1600366|最后，在View中，您将像这样编写代码。|1600367|@Html.DropDownList("DropDownListMainCategory",+(IEnumerable<SelectListItem>)ViewBag.MainCategories,+new+{+@class+=+"form-control",+onchange+=+"this.form.submit();"+})|1600368|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

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

first add this class to your project

<pre><code>public class SelectListDefaults
{
 private IList&lt;SelectListItem&gt; getDefaultItems = new List&lt;SelectListItem&gt;();

 public SelectListDefaults()
 {
 this.AddDefaultItem("(All)", "-1");
 }
 public SelectListDefaults(string text, string value)
 {
 this.AddDefaultItem(text, value);
 }
 public IList&lt;SelectListItem&gt; GetDefaultItems
 {
 get
 { 
 return getDefaultItems;
 }

 }
 public void AddDefaultItem(string text, string value)
 { 
 getDefaultItems.Add(new SelectListItem() { Text = text, Value = value }); 
 }
}
</code></pre>

Now in Controller Action you can do like this

<pre><code> // 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"));
</code></pre>

And finally in View you will code like this.

<pre><code>@Html.DropDownList("DropDownListMainCategory", (IEnumerable&lt;SelectListItem&gt;)ViewBag.MainCategories, new { @class = "form-control", onchange = "this.form.submit();" })
</code></pre>

blocks|key|1385588|text|一种解决方法是使用@tvanfosson的答案(选定的答案)，并使用JQuery+(或Javascript)将选项的值设置为0：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1385589|$(document).ready(function+()+{
++++++++$('#DropDownListId+option:first').val('0');
++++});|code-block|syntax|javascript|1385590|希望这能有所帮助。|1385591|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

A work-around is to use @tvanfosson's answer (the selected answer) and use JQuery (or Javascript) to set the option's value to 0:

<pre><code>$(document).ready(function () {
 $('#DropDownListId option:first').val('0');
 });
</code></pre>

Hope this helps.

blocks|key|1600426|text|尝试类似以下代码的代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1600427|MyDAO+MyDAO+=+new+MyDAO();++++
List<MyViewModel>+_MyDefault+=+new+List<MyViewModel>()+{
++++++++++++++++new+MyViewModel{
++++++++++++++++++++Prop1=+"All",
++++++++++++++++++++Prop2+=+"Select+all"
++++++++++++++++}
++++++++++++};
++++++++++++ViewBag.MyViewBag=+
++++++++++++++++new+SelectList(MyDAO
++++++++++++++++.MyList().Union(
++++++++++++++++++++_MyDefault
++++++++++++++++++++),+"Prop1",+"Prop2");|code-block|syntax|javascript|1600428|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try something like the following code: 

<pre><code>MyDAO MyDAO = new MyDAO(); 
List&lt;MyViewModel&gt; _MyDefault = new List&lt;MyViewModel&gt;() {
 new MyViewModel{
 Prop1= "All",
 Prop2 = "Select all"
 }
 };
 ViewBag.MyViewBag= 
 new SelectList(MyDAO
 .MyList().Union(
 _MyDefault
 ), "Prop1", "Prop2");
</code></pre>

blocks|key|1600177|text|我不知道如果其他人有更好的选择。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1600178|<%25+if+(Model.VariableName+==+""+%7C%7C+Model.VariableName==+null)+{+%25>
+++<%25=+html.DropDpwnList("ListName",+((SelectList)+ViewData["viewName"],+"",+
++++++++new{stlye="+"})%25>
<%25+}+else{+%25>
<%25=+html.DropDpwnList("ListName",+((SelectList)+ViewData["viewName"],+
++++++++Model.VariableName,+new{stlye="+"})%25>
<%25+}>|code-block|syntax|javascript|1600179|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I don't if anybody else has a better option...

<pre><code>&lt;% if (Model.VariableName == "" || Model.VariableName== null) { %&gt;
 &lt;%= html.DropDpwnList("ListName", ((SelectList) ViewData["viewName"], "", 
 new{stlye=" "})%&gt;
&lt;% } else{ %&gt;
&lt;%= html.DropDpwnList("ListName", ((SelectList) ViewData["viewName"], 
 Model.VariableName, new{stlye=" "})%&gt;
&lt;% }&gt;
</code></pre>

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 --"

Something like

<pre><code>SelectList list = new SelectList(repository.func.ToList());
ListItem li = new ListItem(value, value);
list.items.add(li);
</code></pre>

Can this be done?

How can I add an item to a SelectList in ASP.net MVC

基本上，我希望在SelectList的开头插入一项，其默认值为0，文本值为“-- Select One --”就像这样SelectList list = new SelectList(repository.func.ToList());ListItem li = new ListItem(value, value);list.items.add(li);这可以做到吗？

问如何在ASP.net MVC中将项添加到SelectList
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问如何在ASP.net MVC中将项添加到SelectListEN

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问如何在ASP.net MVC中将项添加到SelectList
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