Cast IList to List

Question

I am trying to cast IList type to List type but I am getting error every time.

List<SubProduct> subProducts= Model.subproduct;

Model.subproduct returns IList<SubProduct>.

it's best to program against the interface (IList) instead of the implimentation (List). It's an unneeded cast to go to List. You now have to add error handling if on the off chance an implementation of IList, which is not a List, enteres that code path. — Brian Leahy, Feb 05 '10 at 14:35
Yeah, but `IList` doesn't have stuff that `List` has, for example `AddRange` — Serj Sagan, Nov 20 '17 at 16:45

score 154 · Accepted Answer · answered Feb 05 '10 at 13:08

154

Try

List<SubProduct> subProducts = new List<SubProduct>(Model.subproduct);

or

List<SubProduct> subProducts = Model.subproducts as List<SubProduct>;

answered Feb 05 '10 at 13:08

Pbirkoff

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This is the right answer, but is there a reason that you want to deal with a List instead of IList? Most of the times using IList is a better choice. – Keith Rousseau Feb 05 '10 at 14:25
3

IList subProducts= Model.subproduct; – Brian Leahy Feb 05 '10 at 14:31
5

@KeithRousseau I ran into the issue when needing to utilize the AddRange() method. – ScubaSteve May 08 '15 at 19:02
16

The second option is not safe, because it assumes that `Model.subproducts` is already of type `List` under the covers. If it's a different implementation of `IList`, such as `ReadOnlyCollection`, it will silently return null and will likely cause a very confusing `NullReferenceException` later in the program execution. And really, if we know that it's always going to be a `List`, then what's the point of returning an `IList` in the first place? – sstan Nov 27 '17 at 13:42

Mark Seemann · Answer 2 · 2018-11-14T18:59:48.893

35

How about this:

List<SubProduct> subProducts = Model.subproduct.ToList();

edited Nov 14 '18 at 18:59

answered Feb 05 '10 at 13:09

Mark Seemann

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Be aware that ToList() creates a copy with possible performance and memory impact. – fose Nov 21 '21 at 15:28

score 18 · Answer 3 · answered Dec 17 '13 at 16:52

18

In my case I had to do this, because none of the suggested solutions were available:

List<SubProduct> subProducts = Model.subproduct.Cast<SubProduct>().ToList();

answered Dec 17 '13 at 16:52

bluish

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score 5 · Answer 4 · edited Dec 17 '13 at 15:49

5

List<SubProduct> subProducts= (List<SubProduct>)Model.subproduct;

The implicit conversion failes because List<> implements IList, not viceversa. So you can say IList<T> foo = new List<T>(), but not List<T> foo = (some IList-returning method or property).

edited Dec 17 '13 at 15:49

bluish

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answered Feb 05 '10 at 13:08

Webleeuw

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Jason Landbridge · Answer 5 · 2019-10-23T22:22:22.110

2

If you have an IList containing interfaces, you can cast it like this:

List to IList

List<Foo> Foos = new List<Foo>(); 
IList<IFoo> IFoos = Foos.ToList<IFoo>();

IList to List

IList<IFoo> IFoos = new List<IFoo>();
List<Foo> Foos = new List<Foo>(IFoos.Select(x => (Foo)x));

This assumes Foo has IFoo interfaced.

edited Oct 23 '19 at 22:22

answered Oct 13 '19 at 15:19

Jason Landbridge

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score 0 · Answer 6 · edited Jun 07 '17 at 12:34

0

List<ProjectResources> list = new List<ProjectResources>();        
IList<ProjectResources> obj = `Your Data Will Be Here`;
list = obj.ToList<ProjectResources>();

This Would Convert IList Object to List Object.

edited Jun 07 '17 at 12:34

Peter Bruins

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answered Jun 09 '16 at 07:26

Hudhaifa Yoosuf

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score 0 · Answer 7 · edited Apr 08 '19 at 23:24

The other answers all recommend to use AddRange with an IList.

A more elegant solution that avoids the casting is to implement an extension to IList to do the job.

In VB.NET:

<Extension()>
Public Sub AddRange(Of T)(ByRef Exttype As IList(Of T), ElementsToAdd As IEnumerable(Of T))
   For Each ele In ElementsToAdd
      Exttype.Add(ele)
   Next
End Sub

And in C#:

public void AddRange<T>(this ref IList<T> Exttype, IEnumerable<T> ElementsToAdd)
{
    foreach (var ele in ElementsToAdd)
    {
        Exttype.Add(ele);
    }
}

score -1 · Answer 8 · edited Apr 05 '23 at 15:33

-1

public async Task<List<TimeAndAttendanceShift>> FindEntitiesByExpression(Expression<Func<TimeAndAttendanceShift, bool>> predicate)
{
    IList<TimeAndAttendanceShift> result = await _dbContext.Set<TimeAndAttendanceShift>().Where(predicate).ToListAsync<TimeAndAttendanceShift>();
    return result.ToList<TimeAndAttendanceShift>();
}

edited Apr 05 '23 at 15:33

The_Black_Smurf

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answered Dec 29 '19 at 21:33

Golden Lion

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score -3 · Answer 9 · answered Oct 27 '17 at 12:01

-3

This is the best option to cast/convert list of generic object to list of string.

object valueList;
List<string> list = ((IList)valueList).Cast<object>().Select(o => o.ToString()).ToList();

answered Oct 27 '17 at 12:01

Ghebrehiywet

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valueList must be list of object – Nov 10 '17 at 07:50

Cast IList to List

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