asp.net mvc dropdownlist no ViewData item

问题

i start to study mvc, try to add dropdownlist, make construction

<%= Html.DropDownList("ddl") %>

but it show error

There is no ViewData item of type 'IEnumerable' that has the key 'ddl'

why? i use simple code, only pass name parameter, so why the error?

回答1:

"There is no ViewData item of type 'IEnumerable'"

It means that helper method is expecting an item of type 'IEnumerable' for e.g, List<> with an Id 'ddl'

If you are trying to display a DropDownList which has items from some static source, here is one way to do this.

          // create new IEnummerable 
          List<string> ddl = 
          new List<string>(new [] {"item1","item2" };   

          // add Items        
          ddl.Add("Item1");
          ddl.Add("Item2");

          // return View which holds ddl now
          ViewData["ddl "] = ddl ;
          return View();

For more insight have a look at

Understanding HTML Helpers
How to create a DropDownList with ASP.NET MVC

回答2:

Actually Html.DropDownList is an HTML helper that create html select element. When you pass ddl as argument it expects to get an array or list or something like that (an object implementing IEnumerable interface) to populate the dropdownlist. try it like this:

In Controller:

ViewData["ddl"]=new string[]{'Jan',  'Feb','Mar','Apr'.......'Dec'};

then it will create a select element containing the given values. For more information read this article.

回答3:

Here is an example of adding a DropDownList in ASP.NET-MVC. You need to provide an item of type 'IEnumerable' with a key 'dll' in the ViewData, as the error says.

来源：https://stackoverflow.com/questions/2308731/asp-net-mvc-dropdownlist-no-viewdata-item

标签

asp.net-mvc

drop-down-menu

viewdata