问题
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
SelectList list = new SelectList(repository.func.ToList());
ListItem li = new ListItem(value, value);
list.items.add(li);
Can this be done?
回答1:
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.
<%= Html.DropDownList( "DropDownValue",
(IEnumerable<SelectListItem>)ViewData["Menu"],
"-- Select One --" ) %>
回答2:
I got this to work by Populating a SelectListItem, converting to an List, and adding a value at index 0.
List<SelectListItem> items = new SelectList(CurrentViewSetups, "SetupId", "SetupName", setupid).ToList();
items.Insert(0, (new SelectListItem { Text = "[None]", Value = "0" }));
ViewData["SetupsSelectList"] = items;
回答3:
This is possible.
//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4:
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()
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5:
Here html helper for you
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6:
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
You can custome the text,value or even the index of the item you need to insert
回答7:
The .ToList().Insert(..) method puts an element into your List. Any position can be specified. After ToList just add .Insert(0, "- - First Item - -")
Your code
SelectList list = new SelectList(repository.func.ToList());
ListItem li = new ListItem(value, value);
list.items.add(li);
New Code
SelectList list = new SelectList(repository.func.ToList().Insert(0, "- - First Item - -"));
ListItem li = new ListItem(value, value);
list.items.add(li);
回答8:
May not sound very elegant, but I usually do something like this:
var items = repository.func.ToList();
items.Insert(0, new funcItem { ID = 0, TextValue = "[None]" });
ViewBag.MyData = new SelectList(items);
回答9:
Okay I like clean code so I made this an extension method
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):
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10:
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
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
// 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.
@Html.DropDownList("DropDownListMainCategory", (IEnumerable<SelectListItem>)ViewBag.MainCategories, new { @class = "form-control", onchange = "this.form.submit();" })
回答11:
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:
$(document).ready(function () {
$('#DropDownListId option:first').val('0');
});
Hope this helps.
回答12:
Try something like the following code:
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");
回答13:
I don't if anybody else has a better option...
<% if (Model.VariableName == "" || Model.VariableName== null) { %>
<%= html.DropDpwnList("ListName", ((SelectList) ViewData["viewName"], "",
new{stlye=" "})%>
<% } else{ %>
<%= html.DropDpwnList("ListName", ((SelectList) ViewData["viewName"],
Model.VariableName, new{stlye=" "})%>
<% }>
来源：https://stackoverflow.com/questions/668589/how-can-i-add-an-item-to-a-selectlist-in-asp-net-mvc