C# List to ICollection

Question

This is weird, I'm trying to initalize my ICollection with List in my constructor and this happens:

Schedules = new List<BookingSchedule>(); //OK
CateringItems = new List<CateringItem>(); //Not

The properties:

public virtual ICollection<BookingSchedule> Schedules { get; set; }
public virtual ICollection<BookedCateringItem> CateringItems { get; set; }

Error:

Error   1   Cannot implicitly convert type
'System.Collections.Generic.List<MyApp.Models.CateringItem>' to  
'System.Collections.Generic.ICollection<MyApp.Models.BookedCateringItem>'. 
An explicit conversion exists (are you missing a cast?)

I can't see the difference between the two. I'm going insane trying to figure this out. Any idea?

You are trying to assign list of `BookedCateringItem` to collection of `CateringItem`. Types not match - that's the difference — Sergey Berezovskiy, Jan 10 '14 at 09:42
You need to read about `Covariance`. see http://tomasp.net/blog/variance-explained.aspx/ — haim770, Jan 10 '14 at 09:42
@haim770 I thought it's about compatibility of ICollection and List, I focused on that too much I ignored the type of the list I was trying to initialize. — kazinix, Jan 10 '14 at 09:44

helb · Answer 1 · 2014-01-10T12:19:56.920

19

You can only convert List<T1> to ICollection<T2> if the types T1 and T2 are the same. Alternatively, you can convert to the non-generic ICollection

ICollection CateringItems = new List<CateringItem>(); // OK

edited Jan 10 '14 at 12:19

answered Jan 10 '14 at 09:53

helb

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Done. And +1 for the extra suggestion about the non-generic `ICollection`, which in certain circumstances (WPF view-models) can be desirable. – O. R. Mapper Jan 10 '14 at 12:25

score 4 · Answer 2 · answered Jan 10 '14 at 09:43

4

    public virtual ICollection<BookedCateringItem> CateringItems { get; set; }
    CateringItems = new List<CateringItem>();

It's different types, BookedCateringItem and CateringItem. You need to change one of them to be the other type.

answered Jan 10 '14 at 09:43

EMB

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score 3 · Accepted Answer · edited Jan 10 '14 at 12:37

3

your CateringItems is a collection of BookedCateringItem, while initializing, you initialized a list of CateringItem.

apparently they are not compatible...

edited Jan 10 '14 at 12:37

Lloyd

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answered Jan 10 '14 at 09:42

Rex

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score 0 · Answer 4 · answered Jan 10 '14 at 09:46

0

You want assign List<CateringItem> to ICollection<BookedCateringItem> So you can not.

answered Jan 10 '14 at 09:46

C# List to ICollection

4 Answers4

Linked