Doing a Cast Within a LINQ Query

Question

Is it possible to do a cast within a LINQ query (for the compiler\'s sake)?

The following code isn\'t terrible, but it would be nice to make it into one query:

Answer 1

Depending on what you are trying to do, one of these might do the trick:

List<Line> parentLineList1 =
  (from t in content.ChildControls.OfType<TabSection>()
   from p in t.ChildControls.OfType<Paragraph>()
   from pl in p.ChildControls.OfType<Line>()
   select pl).ToList();

List<Line> parentLineList2 =
  (from TabSection t in content.ChildControls
   from Paragraph p in t.ChildControls
   from Line pl in p.ChildControls
   select pl).ToList();

Note that one uses OfType<T>(), which you were using. This will filter the results and return only the items of the specified type. The second query implicitly uses Cast<T>(), which casts the results into the specified type. If any item cannot be cast, an exception is thrown. As mentioned by Turbulent Intellect, you should refrain from calling ToList() as long as possible, or try to avoid it altogether.

Answer 2

List<TabSection> tabList = (from t in content.ChildControls
                            let ts = t as TabSection
                            where ts != null
                            select ts).ToList();

Answer 3

yes you can do the following:

List<TabSection> tabList = (from t in content.ChildControls
                            where t as TabSection != null
                            select t as TabSection).ToList();

Answer 4

Try this:

from TabSection t in content.ChildControls

Also, even if this were not available (or for a different, future scenario you may encounter), you wouldn't be restricted to converting everything to Lists. Converting to a List causes query evaluation on the spot. But if you removing the ToList call, you could work with the IEnumerable type, which would continue to defer the execution of the query until you actually iterate or store in a real container.

Answer 5

And here's the query method form.

List<Line> parentLineList =
  content.ChildControls.OfType<TabSections>()
    .SelectMany(t => t.ChildControls.OfType<Paragraph>())
    .SelectMany(p => p.ChildControls.OfType<Line>())
    .ToList();