implement IEnumerator and IEnumerable in ICollection

Question

I am very new to this ICollection stuff and need some guidance of how to implement the IEnumerable and IEnumerator. I have checked Microsoft documentation and I think I understand what was said there (I think). But when I tried to implement it in my case, I was a bit confused and may need some clarification.

Basically, I declared a class T, then another class Ts which implemented ICollection. In Ts, I have a dictionary.

From the main program, I would like to initialize the class Ts like this: Ts ts= new Ts(){{a,b}, {c,d}};

so, my questions are:

1) is it legal to do that? It appears that it is as the compiler did not complaint although I have not run the test because I have not thoroughly implement IEnumerable and IEnumerator, which brought to my 2nd question

2) How do I implement IEnumerable and IEnumerator?

Below is my pseudo code to illustrate my points.

        public class T
        {
           string itemName;
           int    quantity;
           .....
           public T(string s, int q)
           { 
              .....
           }
        }
        public class Ts: ICollection
        {
            private Dictionary<string, T> inventory= new Dictionary<string,T>();

            public void Add(string s, int q)
            {
                inventory.Add(s, new T(s,q));
            }

             public IEnumerator<T> GetEnumerator()
            { 
            // please help              
            }

            IEnumerator IEnumerable.GetEnumerator()
            {
            // what is the proper GetEnumerator here
            }
            ...
            implement other method in ICollection
        } 

        extract from the main program
        public Ts CollectionOfT = new Ts(){{"bicycle",100},{"Lawn mower",50}};
        .........

Answer 1

Honestly you don't need to build your own collection "wrapper" around a Dictionary, but if you must, you can delegate pretty much all the calls to the dictionary for the implementation of the ICollection interface. Hope this helps

        public class Ts: ICollection<T>
    {
        private Dictionary<string, T> inventory= new Dictionary<string,T>();

        //public void Add(string s, int q)
        //{
        //    inventory.Add(s, new T(s,q));
        //} 
        public void Add(T item)
        {
            inventory.Add(item.ItemName,item);
        }
        public void Add(string s, int q)
        {
            inventory.Add(s, new T(s, q));
        }

        public void Clear()
        {
            inventory.Clear();
        }

        public bool Contains(T item)
        {
            return inventory.ContainsValue(item);
        }

        public void CopyTo(T[] array, int arrayIndex)
        {
            inventory.Values.CopyTo(array, arrayIndex);
        }

        public int Count
        {
            get { return inventory.Count; }
        }

        public bool IsReadOnly
        {
            get { return false; }
        }

        public bool Remove(T item)
        {
            return inventory.Remove(item.ItemName);
        }

        public System.Collections.Generic.IEnumerator<T> GetEnumerator()
        {
            return inventory.Values.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return inventory.Values.GetEnumerator();
        }
    } 
   class Program
   {
        Ts ts = new Ts { { "a", 1 }, { "b", 2 } };
        foreach (T t in ts)
        {
            Console.WriteLine("{0}:{1}",t.ItemName,t.Quantity);
        }
    }

Answer 2

The proper implementation is to cast your collection to IEnumerable in the explicit implementation:

IEnumerator IEnumerable.GetEnumerator() { 
    return ((IEnumerable)your_collection_here).GetEnumerator();
}

For the generic version, call GetEnumerator on your collection:

public IEnumerator<T> GetEnumerator() {
    return your_collection_here.GetEnumerator();
}

You must have something that is backing your custom collection.. such as a List, Array, etc. Use that in those implementations.