Could not find an implementation of the query pattern Error

Question

Given

   var selectedItems = listBoxControl1.SelectedItems;
   var selectedItemsList = (from i in selectedItems
                             select i).ToList();

I receive Error

Could not find an implementation of the query pattern for source type 'DevExpress.XtraEditors.BaseListBoxControl.SelectedItemCollection'. 'Select' not found. Consider explicitly specifying the type of the range variable 'i'.

using system.LINQ Done

I can use foreach so it must implement IEnumerable. I prefer to use LINQ over foreach to gather each string, if possible.

I want to take the ToString() values for each SelectedItem in the list box control and stick them in a List<string>. How can I do it?

for a foreach to work the type of the object after the keyword in simply needs to have a mthod called GetEnumerator() which in turn returns an object of a type that has a MoveNext() method and a Current property. It does **not** need to implement IEnumerable — Rune FS, Mar 21 '12 at 14:05

Jon Skeet · Accepted Answer · 2012-03-21T14:01:42.860

14

I can use foreach so it must implement IEnumerable.

That's not actually true, but it's irrelevant here. It does implement IEnumerable, but not IEnumerable<T> which is what LINQ works over.

What's actually in the list? If it's already strings, you could use:

var selectedItemsList = selectedItems.Cast<string>().ToList();

Or if it's "any objects" and you want to call ToString you can use:

var selectedItemsList = selectedItems.Cast<object>()
                                     .Select(x => x.ToString())
                                     .ToList();

Note that the call to Cast is why the error message suggested using an explicitly typed range variable - a query expression starting with from Foo foo in bar will be converted to bar.Cast<Foo>()...

edited Mar 21 '12 at 14:01

answered Mar 21 '12 at 13:53

Jon Skeet

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What is required to implement foreach? – P.Brian.Mackey Mar 21 '12 at 14:04
1

@P.Brian.Mackey: A method called `GetEnumerator()` which is declared to return a type with suitable `MoveNext()` and `Current` members. It doesn't have to implement `IEnumerable`. Using a type with a `Current` property of (say) `int` was a way to avoid boxing while iterating before generics. – Jon Skeet Mar 21 '12 at 14:06
just login to up cast this – Tawfik Khalifeh Jul 12 '13 at 15:48

score 7 · Answer 2 · edited Mar 21 '12 at 13:55

7

For LINQ to work, you need an IEnumerable<T>, straight IEnumerable isn't enough. Try:

var selectedItems = listboxControl1.SelectedItems.Cast<T> //where T is the actual type of the item

edited Mar 21 '12 at 13:55

M.Babcock

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answered Mar 21 '12 at 13:55

Rich

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score 1 · Answer 3 · answered Mar 21 '12 at 14:00

1

Try just

var result = listBoxControl1.SelectedItems.Cast<MyItemType>().ToList();

answered Mar 21 '12 at 14:00

Olivier Jacot-Descombes

104,806
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Could not find an implementation of the query pattern Error

3 Answers3

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