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.