How to cast C#'s linq WHERE statement?

I have a class Literal and a Tag is inheriting from it.

I would like to do the following but I am getting

Unable to cast object of type 'Wher开发者_如何转开发eListIterator`1[Core.Literal]' to type 'System.Collections.Generic.List`1[Core.Tag]'.

 private List<Literal> literals;
public List<Tag> Tags
        {
            get { return (List<Tag>)literals.Where(x => x is Tag); }
        }

thanks

You would be better off doing:

literals.OfType<Tag>().ToList();

This gives you a List<Tag>.

You can also do:

var asList = new List<Tag>(literals.OfType<Tag>());

Casting simply does not work because LINQ works in terms of either IEnumerable<T> or IQueryable<T> which neither use List as a backing implementation for the results. The second method I posted uses a constructor overload of List<T> the takes in an IEnumerable<T> as its initial collection of objects. Also in this scenario the OfType<T> method from LINQ is a much cleaner, shorter form of essentially filtering a list with Where(x -> x is T).

Also, OfType<T> in this scenario is a much better idea, because the result is an IEnumerable<T> of your target type. Where(x => x is T) will return an IEnumerable<T> of the original source's type. So that's why (List<Tag>)literals.Where(x => x is Tag).ToList() emit an error for invalid casts.

More information on ToList

More information on OfType

literals.Select(x => x as Tag).Where(x => x != null).ToList()

Note that this will return new list. You won't be able to do where and modify original list by this. Also this can be done like this: literals.OfType<Tag>().ToList() and it will return IList<Tag>

Update: modified type

List<Tag>)literals.Where(x => x is Tag).ToList();

or even better :

literals.OfType<Tag>();

then you can create a new list from it:

new List<Tag>(literals.OfType<Tag>());

Depending on the effect you want you could do this:

public List<Tag> Tags
{
    get { return literals.Where(x => x is Tag).ToList(); }
}

Do realize that this is not a cast but the creation of a list!

How about adding ToList()?

Your getter becomes: literals.Where(x => x is Tag).ToList();

try the following:

literals.Where(x => x is Tag).Cast<Tag>().ToList();

it works if Tag is derived from Literal

The Where method returns the same type as the source, so you would have to cast each item, then use the ToList method to create a list from the result:

return literals.Where(x => x is Tag).Select(x => (Tag)x).ToList();

You can also us the OfType method:

return literals.OfType<Tag>().ToList();