Asynchronous Where Filter with Linq

Question

I have a List of elements which is populated through an async call of a WebService (no problem there).

I need to filter that list in order to show something on the application view. I tried this:

List<DateTime> dates = EventsDates.Where(x => x.Day == tmp.Day && x.Month == tmp.Month && x.Year == tmp.Year).ToList();

I also tried using the Select function of LINQ. The problem is that any time this code is called, the EventsDates list isn't populated, the WebService hasn't responded yet.

How could I try to filter the EventsDates list asynchronously?

Answer 1

"Where" shouldn't be async, you need to do EventsDates fill awaitable. Something like this:

EventsDates = await YourWebServiceMethodCall();
List<DateTime> dates = EventsDates.Where (x => x.Day == tmp.Day && x.Month == tmp.Month && x.Year == tmp.Year).ToList();

Answer 2

You can call it asynchronously like this but as others have stated you need to await the eventDates to unwrap the response from the service before you use it. @Dmitry's answer is correct. I just put this here to answer your question of how to use Where asynchronously in case you need it in the future.

using System.Data.Entity;

List<DateTime> dates = await EventsDates.Where(x => x.Day == tmp.Day && x.Month == tmp.Month && x.Year == tmp.Year).ToListAsync();

You can also do this:

var list = someCollection.Where(async x => x.Prop == await SomeLongRunningProcess());

Answer 3

It looks like you aren't awaiting the result to populate EventDates.