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>.

Postfree

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. – Worthwhile

Yeah, but IList doesn't have stuff that List has, for example AddRange – Unintelligible

Answer 1

Try

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

or

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

Climate

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. – Stewardess

IList<SubProduct> subProducts= Model.subproduct; – Worthwhile

@KeithRousseau I ran into the issue when needing to utilize the AddRange() method. – Fortuity

The second option is not safe, because it assumes that Model.subproducts is already of type List<SubProduct> under the covers. If it's a different implementation of IList<SubProduct>, such as ReadOnlyCollection<SubProduct>, 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<T>, then what's the point of returning an IList<T> in the first place? – Mage

Answer 2

How about this:

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

Bundelkhand

Be aware that ToList() creates a copy with possible performance and memory impact. – Farron

Answer 3

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

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

Trabeated

Answer 4

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).

Westberry

Answer 5

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.

Epidaurus

Answer 6

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.

Roley

Answer 7

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);
    }
}

Devora

Answer 8

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>();
}

Heyward

Answer 9

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();

Briareus

valueList must be list of object – Nikianikita