How to use foreach on a list of lists that on another class

Question

public class ItemCollection
{
    List<AbstractItem> LibCollection;

    public ItemCollection()
    {
        LibCollection = new List<AbstractItem>(); 
    }

    public List<AbstractItem> ListForSearch()
    {
        return LibCollection;
    }

and in another class i wrote this:

public class Logic
{
    ItemCollection ITC;

    List<AbstractItem> List;

    public Logic()
    {
        ITC = new ItemCollection();   

        List = ITC.ListForSearch();    
    }

    public List<AbstractItem> search(string TheBookYouLookingFor)
    {
        foreach (var item in List)
        {
          //some code..
        }

and the list in the foreach is contain nothing and i need to work on this list (this list is should be the same content as libcollection) for the search method

Answer 1

If ItemCollection serves no purpose other than to own the List<AbstractItem> , then the class should probably be removed altogether and just use List<AbstractItem> instead.

If ItemCollection has another purpose and others shouldn't have access to the underlying List<AbstractItem> , it can implement IEnumerable<AbstractItem> :

class ItemCollection : IEnumerable<AbstractItem>
{
    List<AbstractItem> LibCollection;

    public ItemCollection() {
        this.LibCollection = new List<AbstractItem>();
    }

    IEnumerator<AbstractItem> IEnumerable<AbstractItem>.GetEnumerator() {
        return this.LibCollection.GetEnumerator();
    }

    IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        return ((IEnumerable)this.LibCollection).GetEnumerator();
    }
}

class Logic
{
    ItemCollection ITC;

    public Logic() {
        ITC = new ItemCollection();
    }

    public List<AbstractItem> Search(string TheBookYouLookingFor) {
        foreach (var item in this.ITC) {
            // Do something useful
        }
        return null; // Do something useful, of course
    }
}

Otherwise, you may want to expose LibCollection directly and let other code enumerate over that:

class ItemCollection
{
    public List<AbstractItem> LibCollection { get; private set; }

    public ItemCollection() {
        this.LibCollection = new List<AbstractItem>();
    }
}

class Logic
{
    ItemCollection ITC;

    public Logic() {
        ITC = new ItemCollection();
    }

    public List<AbstractItem> Search(string TheBookYouLookingFor) {
        foreach (var item in this.ITC.LibCollection) {
            // Do something useful
        }
        return null; // Do something useful
    }
}