How can I convert IEnumerable<T> to List<T> in C#?

Question

I am using LINQ to query a generic dictionary and then use the result as the datasource for my ListView (WebForms).

Simplified code:

Dictionary<Guid, Record> dict = GetAllRecords();
myListView.DataSource = dict.Values.Where(rec => rec.Name == "foo");
myListView.DataBind();

I thought that would work but in fact it throws a System.InvalidOperationException:

ListView with id 'myListView' must have a data source that either implements ICollection or can perform data source paging if AllowPaging is true.

In order to get it working I have had to resort to the following:

Dictionary<Guid, Record> dict = GetAllRecords();
List<Record> searchResults = new List<Record>();

var matches = dict.Values.Where(rec => rec.Name == "foo");
foreach (Record rec in matches)
    searchResults.Add(rec);

myListView.DataSource = searchResults;
myListView.DataBind();

Is there a small gotcha in the first example to make it work?

(Wasn't sure what to use as the question title for this one, feel free to edit to something more appropriate)

Answer 1

Try this:

var matches = dict.Values.Where(rec => rec.Name == "foo").ToList();

Be aware that that will essentially be creating a new list from the original Values collection, and so any changes to your dictionary won't automatically be reflected in your bound control.

Answer 2

myListView.DataSource = (List<Record>) dict.Values.Where(rec => rec.Name == "foo");

Answer 3

You might also try:

var matches = new List<Record>(dict.Values.Where(rec => rec.Name == "foo"));

Basically generic collections are very difficult to cast directly, so you really have little choice but to create a new object.

Answer 4

@lomaxx : Your first solution does not work. I can't seem to be able to cast the result from the where clause to a List. It results in the following runtime exception:

*Unable to cast object of type 'd__01[Record]' to type 'System.Collections.Generic.List1[Record]'.*

Your second solution works great and so does Matt Hamiltons's. I've accepted Matt Hamiltons's answer as I found it 'cleaner'.

thank you both.

Answer 5

I tend to prefer using the new Linq syntax:

myListView.DataSource = (
    from rec in GetAllRecords().Values
    where rec.Name == "foo"
    select rec ).ToList();
myListView.DataBind();

Why are you getting a dictionary when you don't use the key? You're paying for that overhead.

Answer 6

@Keith: I'm using a the Guid key in the dictionary somewhere else in my code so I can get a record by record id.

Agree to disagree on the syntax ;)