Question

I having treeView loaded with custom class collection(eg: MyClass). I want return collection of MyClass[] from the checked tree view items and want use LINQ. I try below and it work fine. But i want to write 1 line Linq query without even using the List<>. Any help ? Is it possible to have recursion within the 1 Linq query ?

List<MyClass> items = new List<MyClass>();            
items.AddRange(from node in tvData.Nodes.OfType<TreeNode>().Where((x) => x.Checked)
               select node.Tag as MyClass);

tvData.Nodes.OfType<TreeNode>()
            .ForEach((x => items.AddRange(from item in x.Nodes.OfType<TreeNode>()
                                                        .Where((y) => y.Checked)
                                          select item.Tag as MyClass)));

return items.ToArray();

Note : The treeView having 1 level depth. Every parent node have a set of child nodes and only 1 level.

Answer 1

Try this:

return tvData.Nodes
             .OfType<TreeNode>()
             .SelectMany(x => new[]{ x }.Concat(x.Nodes.OfType<TreeNode>()))
             .Where(x => x.Checked)
             .Select(x => x.Tag as MyClass)
             .ToArray();

A solution for more than one level could look like this:

IEnumerable<TreeNode> GetNodeAndChildren(TreeNode node)
{
    return new[]{ node }.Concat(node.Nodes
                                    .OfType<TreeNode>()
                                    .SelectMany(x => GetNodeAndChildren(x)));
}

return tvData.Nodes
             .OfType<TreeNode>()
             .SelectMany(x => GetNodeAndChildren(x))
             .Where(x => x.Checked)
             .Select(x => x.Tag as MyClass)
             .ToArray();