ASP NET MVC Html DropDownList SelectedValue

Question

I have tried this is RC1 and then upgraded to RC2 which did not resolve the issue      in my controller ViewData  UserId     new SelectList      users        UserId         DisplayName        selectedUserId Value      this has a value   result  the SelectedValue property is set on the object     in my view  lt   Html DropDownList  UserId    SelectList ViewData  UserId     gt    result  all expected options are rendered to the client  but the selected attribute is not set   The item in SelectedValue exists within the list  but the first item in the list is always defaulted to selected   How should I be doing this   Update Thanks to John Feminella s reply I found out what the issue is    UserId  is a property in the Model my View is strongly typed to   When Html DropDownList  UserId  is changed to any other name but  UserId   the selected value is rendered correctly    This results in the value not being bound to the model though

User · Answer

Try this   public class Person       public int Id   get  set        public string Name   get  set        And then   var list   new            new Person   Id   1  Name    Name1          new Person   Id   2  Name    Name2          new Person   Id   3  Name    Name3         var selectList   new SelectList list   Id    Name   2   ViewData  People     selectList   Html DropDownList  PeopleClass    SelectList ViewData  People      With MVC RC2  I get    lt select id  PeopleClass  name  PeopleClass  gt       lt option value  1  gt Name1 lt  option gt       lt option selected  selected  value  2  gt Name2 lt  option gt       lt option value  3  gt Name3 lt  option gt   lt  select gt

User · Answer

This appears to be a bug in the SelectExtensions class as it will only check the ViewData rather than the model for the selected item  So the trick is to copy the selected item from the model into the ViewData collection under the name of the property   This is taken from the answer I gave on the MVC forums  I also have a more complete answer in a blog post that uses Kazi s DropDownList attribute      Given a model  public class ArticleType      public Guid Id   get  set       public string Description   get  set       public class Article       public Guid Id   get  set        public string Name   get  set        public ArticleType   get  set        and a basic view model of   public class ArticleModel        public Guid Id   get  set         public string Name   get  set           UIHint  DropDownList         public Guid ArticleType   get  set        Then we write a DropDownList editor template as follows     lt    Control Language  C   Inherits  System Web Mvc ViewUserControl    gt   lt script runat  server  gt        IEnumerable lt SelectListItem gt  GetSelectList                 var metaData   ViewData ModelMetadata          if  metaData    null                        return null                     var selected   Model is SelectListItem     SelectListItem  Model  Value   Model ToString            ViewData metaData PropertyName    selected           var key   metaData PropertyName    List           return  IEnumerable lt SelectListItem gt  ViewData key          lt  script gt   lt    Html DropDownList null  GetSelectList      gt    This will also work if you change ArticleType in the view model to a SelectListItem  though you do have to implement a type converter as per Kazi s blog and register it to force the binder to treat this as a simple type    In your controller we then have     public ArticleController                  public ActionResult Edit int id                   var entity   repository FindOne lt Article gt  id             var model   builder Convert lt ArticleModel gt  entity              var types   repository FindAll lt ArticleTypes gt               ViewData  ArticleTypeList     builder Convert lt SelectListItem gt  types              return VIew model

User · Answer

You can still name the DropDown as  UserId  and still have model binding working correctly for you    The only requirement for this to work is that the ViewData key that contains the SelectList does not have the same name as the Model property that you want to bind  In your specific case this would be      in my controller ViewData  Users     new SelectList      users        UserId         DisplayName        selectedUserId Value      this has a value     in my view  lt   Html DropDownList  UserId    SelectList ViewData  Users     gt    This will produce a select element that is named UserId  which has the same name as the UserId property in your model and therefore the model binder will set it with the value selected in the html s select element generated by the Html DropDownList helper   I m not sure why that particular Html DropDownList constructor won t select the value specified in the SelectList when you put the select list in the ViewData with a key equal to the property name  I suspect it has something to do with how the DropDownList helper is used in other scenarios  where the convention is that you do have a SelectList in the ViewData with the same name as the property in your model  This will work correctly      in my controller ViewData  UserId     new SelectList      users        UserId         DisplayName        selectedUserId Value      this has a value     in my view  lt   Html DropDownList  UserId    gt

User · Answer

If we don t think this is a bug the team should fix  at lease MSDN should improve the document  The confusing really comes from the poor document of this   In MSDN  it explains the parameters   name as    Type  System String The name of the form field to return    This just means the final html it generates will use that parameter as the name of the select input  But  it actually means more than that   I guess the designer assumes that user will use a view model to display the dropdownlist  also will use post back to the same view model  But in a lot cases  we don t really follow that assumption   Use the example above   public class Person       public int Id   get  set        public string Name   get  set        If we follow the assumption we should define a view model for this dropdownlist related view  public class PersonsSelectViewModel      public string SelectedPersonId      public List lt SelectListItem gt  Persons      Because when post back  only the selected value will post back  so it assume it should post back to the model s property SelectedPersonId  which means Html DropDownList s first parameter name should be  SelectedPersonId    So  the designer thinks that when display the model view in the view  the model s property SelectedPersonId should hold the default value of that dropdown list  Even thought your List lt SelectListItem  Persons already set the Selected flag to indicate which one is selected default   the tml DropDownList will actually  ignore that and rebuild it s own IEnumerable lt SelectListItem  and set the default selected item based on the name   Here is the code from asp net mvc  private static MvcHtmlString SelectInternal this HtmlHelper htmlHelper  ModelMetadata metadata              string optionLabel  string name  IEnumerable lt SelectListItem gt  selectList  bool allowMultiple              IDictionary lt string  object gt  htmlAttributes                 bool usedViewData   false          If we got a null selectList  try to use ViewData to get the list of items      if  selectList    null                selectList   htmlHelper GetSelectData name           usedViewData   true             object defaultValue    allowMultiple    htmlHelper GetModelStateValue fullName  typeof string       htmlHelper GetModelStateValue fullName  typeof string            If we haven t already used ViewData to get the entire list of items then we need to        use the ViewData-supplied value before using the parameter-supplied value      if  defaultValue    null  amp  amp   String IsNullOrEmpty name                 if   usedViewData                        defaultValue   htmlHelper ViewData Eval name                     else if  metadata    null                        defaultValue   metadata Model                       if  defaultValue    null                selectList   GetSelectListWithDefaultValue selectList  defaultValue  allowMultiple                       return tagBuilder ToMvcHtmlString TagRenderMode Normal       So  the code actually went further  it not only try to look up the name in the model  but also in the viewdata   as soon as it finds one  it will rebuild the selectList and ignore your original Selected   The problem is   in a lot of cases  we don t really use it that way   we just want to throw in a selectList with one multiple item s  Selected set true   Of course the solution is simple  use a name that not in the model nor in the viewdata  When it can not find a match  it will use the original selectList and the original Selected will take affect   But i still think mvc should improve it by add one more condition  if   defaultValue    null   amp  amp    selectList Any i  gt i Selected          selectList   GetSelectListWithDefaultValue selectList  defaultValue  allowMultiple       Because  if the original selectList has already had one Selected  why would you ignore that   Just my thoughts

User · Answer

This is how I fixed this problem   I had the following   Controller   ViewData  DealerTypes     Helper SetSelectedValue listOfValues  selectedValue      View   lt   Html DropDownList  DealerTypes   ViewData  DealerTypes   as SelectList   gt    Changed by the following   View    lt   Html DropDownList  DealerTypesDD   ViewData  DealerTypes   as SelectList   gt    It appears that the DropDown must not have the same name has the ViewData name  S weird but it worked

User · Answer

The problems is that dropboxes don t work the same as listboxes  at least the way ASP NET MVC2 design expects  A dropbox allows only zero or one values  as listboxes can have a multiple value selection  So  being strict with HTML  that value shouldn t be in the option list as  selected  flag  but in the input itself   See the following example    lt select id  combo  name  combo  value  id2  gt     lt option value  id1  gt This is option 1 lt  option gt     lt option value  id2  selected  selected  gt This is option 2 lt  option gt     lt option value  id3  gt This is option 3 lt  option gt   lt  select gt    lt select id  listbox  name  listbox  multiple gt     lt option value  id1  gt This is option 1 lt  option gt     lt option value  id2  selected  selected  gt This is option 2 lt  option gt     lt option value  id3  gt This is option 3 lt  option gt   lt  select gt    The combo has the option selected  but also has its value attribute set  So  if you want ASP NET MVC2 to render a dropbox and also have a specific value selected  i e    default values  etc    you should give it a value in the rendering  like this      in my view               lt   Html DropDownList  UserId   selectListItems     SelectList ViewData  UserId      new    Value   selectedUser Id      Your selected value as an additional HTML attribute      gt

User · Answer

In ASP NET MVC 3 you can simply add your list to ViewData     var options   new List lt SelectListItem gt      options Add new SelectListItem   Value    1   Text    1      options Add new SelectListItem   Value    2   Text    2      options Add new SelectListItem   Value    3   Text    3   Selected   true      ViewData  options     options       and then reference it by name in your razor view      Html DropDownList  options     You don t have to manually  use  the list in the DropDownList call   Doing it this way correctly set the selected value for me too   Disclaimer     Haven t tried this with the web forms view engine  but it should work too  I haven t tested this in the v1 and v2  but it might work

User · Answer

The code in the previous MVC 3 post does not work but it is a good start   I will fix it   I have tested this code and it works in MVC 3 Razor C   This code uses the ViewModel pattern to populate a property that returns a List lt SelectListItem gt    The Model class  public class Product       public string Name   get  set        public decimal Price   get  set        The ViewModel class  using System Web Mvc   public class ProductListviewModel       public List lt SelectListItem gt  Products   get  set        The Controller Method  public ViewResult List         var productList   new List lt SelectListItem gt          foreach  Product p in Products                productList Add new SelectListItem                       Value   p ProductId ToString                Text    Product      p Name         p Price ToString                   To set the selected item use the following code                 Note  you should not set every item to selected             Selected   true                        ProductListViewModel productListVM   new ProductListViewModeld         productListVM Products   productList       return View productListVM       The view   model MvcApp ViewModels ProductListViewModel   using  Html BeginForm           Html DropDownList  Products   Model Products      The HTML output will be something like   lt select id  Products  name  Products  gt       lt option value  3  gt Product  Widget 10 00 lt  option gt       lt option value  4  gt Product  Gadget 5 95 lt  option gt   lt  select gt    depending on how you format the output   I hope this helps   The code does work

User · Answer

I managed to get the desired result  but with a slightly different approach  In the Dropdownlist i used the Model and then referenced it  Not sure if this was what you were looking for    Html DropDownList  Example   new SelectList Model FeeStructures   Id    NameOfFeeStructure   Model Matters FeeStructures     Model Matters FeeStructures in above is my id  which could be your value of the item that should be selected

[asp.net-mvc] ASP.NET MVC Html.DropDownList SelectedValue

Examples related to asp.net-mvc