How to cast to a List>

Question

I was doing this first to return a particular set of nodes under the parent node that had id equal to 1 which worked fantastically.

IEnumerable<XElement> world1 = LevelData.root.
                               Elements("world").
                               Where(element => (int?)element.Attribute("id") == 1);

But i needed to do this multiple times and each to have there own instance so i thought to put them into a list but it doesn't even compile telling me error CS0266:

Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.List>'. An explicit conversion exists (are you missing a cast?)

List<IEnumerable<XElement>>[] World = new List<IEnumerable<XElement>>[noofworlds];

        foreach (List<IEnumerable<XElement>> wn in World)
        {
            Debug.WriteLine("World: "+w);

            //this will make a list of all the nodes (elements) within the world specified by the id tag
            World[w] =  LevelData.Root.Elements("world").Where(element => (int?)element.Attribute("id") == 1);//with id == to i
            w++;
        }

So I tried adding the cast List<IEnumerable<XElement>> just before LevelData.root. but then i get a invalidcastexception. I'm at a brick wall on where to go. Any advice?

Your `World` variable is an array of lists of `IEnumerable`s of `XElement`. I'm pretty sure you never want to do that. — juharr, Feb 11 '13 at 21:47

score 5 · Accepted Answer · answered Feb 11 '13 at 21:36

5

The Where method doesn't return a List<>, it returns an IEnumerable<>, which is lazy-evaluated when it is enumerated.

If you want an actual List<> object, stick a .ToList() at the end, and that will do it.

answered Feb 11 '13 at 21:36

David Yaw

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score 4 · Answer 2 · answered Feb 11 '13 at 21:36

var world1 = LevelData.root
                           .Elements("world")
                           .Where(element => (int?)element.Attribute("id") == 1)
                           .ToList();

You need to use ToList() to convert it from IEnumerable, because the IList interface supports more functionality than the IEnumerable interface.

score 2 · Answer 3 · answered Feb 11 '13 at 21:37

2

You can convert an IEnumerable<T> to List<T> by calling ToList()

List<XElement> world1 = LevelData.root
    .Elements("world")
    .Where(element => (int?)element.Attribute("id") == 1)
    .ToList();

answered Feb 11 '13 at 21:37

Khan

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score 2 · Answer 4 · answered Feb 11 '13 at 21:55

Your question is a bit confusing, you seem to have an array of List<IEnumerable<XElement>> and you are trying to assign a IEnumerable<XElement> to it.

If you just want a List of IEnumerable<XElement> this should work

List<IEnumerable<XElement>> World = new List<IEnumerable<XElement>>();
for (int i = 0; i < noofworlds; i++)
{
    World.Add(LevelData.Root.Elements("world").Where(element => (int?)element.Attribute("id") == i));//with id == to i
}

Otherwise tou are going to have to create a new list to add to the array and add the IEnumerable<XElement> to that list.

List<IEnumerable<XElement>>[] World = new List<IEnumerable<XElement>>[noofworlds];
for (int i = 0; i < noofworlds; i++)
{
    World[i] = new List<IEnumerable<XElement>> { (LevelData.Root.Elements("world").Where(element => (int?)element.Attribute("id") == i)) };//with id == to i
}

How to cast to a List>

4 Answers4