无法从“ System.Collections.Generic.IEnumerable”转换为System.Collections.Generic.IEnumerable <string>

Question

I am trying to store a list of multiple values from an object and store it in a dropdownlist by iterating through a loop.

ddlCountries.Items.AddRange((from country in countries
                               select new List<string> {
                               country.Name,
                               country.Slug,
                               country.Iso
                               })).ToList();

However I get this error message with the select keyword:

Argument 1: cannot convert from 'System.Collections.Generic.IEnumerable>' to 'System.Web.UI.WebControls.ListItem[]'

Originally I tested to make sure it can retrieves values from the list using ListItem:

ddlCountries.Items.AddRange((from country in countries
                                     select new ListItem(country.Name, country.Slug))
                                     .ToArray<ListItem>());

This works perfectly fine, however I needed to retrieve an additional field (country.iso). I have searched the forums for a solution but I'm having a difficult time finding ways to solve this issue. Any help on this would be much appreciated.

Answer 1

Well, seeing as the ListItem class contains only Text and Value , you need some way of joining country.Slug and country.Iso into a single string value.

ddlCountries.Items.AddRange((from country in countries
                             select new ListItem(
                                 country.Name,
                                 country.Slug + "," + country.Iso))
                             .ToArray());

This will make it so that you are still generating a ListItem[] instead of a List<List<string>> .

Answer 2

You could try Anonymous Types

var src = from country in countries.AsEnumerable()
          select 
              name = country.Name, 
              slug = country.Slug,
              iso = country.Name + " " + country.slug
ddlCountries.dataSource = src.AsQueryable();
ddlCountries.DataBind();

Answer 3

List expects only one String per item in the List. Your new type has three fields. You could instead try this:

ddlCountries.Items.AddRange(
       ( from country in countries
         select new { country.Name, country.Slug, country.Iso } 
       ).ToList()
    );

But then, why do you need to create a List? Have you tried binding the query directly as the datasource to your drop-down-list? You could then define which field (Name for example) as the Visible field, and Slug/Iso as the Value Field - which is something that you would have to do even now.

Hope this helps.