C# - How to implement IEnumerator on a class

Question

How to implement IEnumerator on this class so that I can use it in foreach loop.

public class Items
    {
        private Dictionary<string, Configuration> _items = new Dictionary<string, Configuration>();

        public Configuration this[string element]
        {
            get
            {

                if (_items.ContainsKey(element))
                {
                    return _items[element];
                }
                else
                {
                    return null;
                }
            }

            set
            {
                _items[element] = value;
            }
        }
   }

In this example Configuration is a simple class with few properties.

possible duplicate of [How would you implement the IEnumerator interface?](http://stackoverflow.com/questions/53967/how-would-you-implement-the-ienumerator-interface) — Alastair Pitts, Aug 02 '11 at 07:10

score 16 · Accepted Answer · answered Aug 02 '11 at 07:19

Just an example to implement typesafe IEnumerable and not IEnumerator which you will be able to use in foreach loop.

   public class Items : IEnumerable<Configuration>
    {
        private Dictionary<string, Configuration> _items = new Dictionary<string, Configuration>();


        public void Add(string element, Configuration config) {
            _items[element] = config;
        }

        public Configuration this[string element]
        {
            get
            {

                if (_items.ContainsKey(element))
                {
                    return _items[element];
                }
                else
                {
                    return null;
                }
            }

            set
            {
                _items[element] = value;
            }
        }

        public IEnumerator<Configuration> GetEnumerator()
        {
            return _items.Values.GetEnumerator();
        }

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return _items.Values.GetEnumerator();
        }
    }

Regards.

You just use the Implementation of the Dictionary Class, so you are technically not implementing IEnumerator :-). — Sebastian, Oct 25 '16 at 12:08
@Sebastian - I did it for another collection here: http://stackoverflow.com/questions/3823848/creating-a-very-simple-linked-list/42206589#42206589 . HTH. — jacoblambert, Feb 14 '17 at 18:15
I comment here, because I used to always get this page via Google search whenever I wanted to implement an enumerator and was frustrated by what you point out. Thanks. — jacoblambert, Feb 14 '17 at 18:37

score 6 · Answer 2 · answered Aug 02 '11 at 07:34

You should be able to implement IEnumerator like this:

public class Items : IEnumerator<KeyValuePair<string, Configuration>>  
{        
    private Dictionary<string, Configuration> _items = new Dictionary<string, Configuration>();        
    public Configuration this[string element]       
    {            
        get
        {
            if (_items.ContainsKey(element))
            {
                return _items[element];
            }
            else
            {
                return null;
            }
        }
        set
        {
             _items[element] = value;
        }
    }

    int current;
    public object Current
    {
        get { return _items.ElementAt(current); }
    }

    public bool MoveNext()
    {
        if (_items.Count == 0 || _items.Count <= current)
        {
            return false;
        }
        return true;
    }

    public void Reset()
    {
        current = 0;
    }

    public IEnumerator GetEnumerator()
    {
        return _items.GetEnumerator();
    }

    KeyValuePair<string, Configuration> IEnumerator<KeyValuePair<string, Configuration>>.Current
    {
        get { return _items.ElementAt(current); }
    }

    public void Dispose()
    {
        //Dispose here
    }
}

But as already noted you could also just implement IEnumerable.

Like Tigran you just using the Enumator of the Dictionary Class. — Sebastian, Oct 25 '16 at 12:09
Tried to implement one myself with your post, but noticed your current never gets incremented. I think you wanted that to do in MoveNext() ? — radonthetyrant, Feb 06 '17 at 11:37
The variable 'current' has to be initialized with -1 (both in the constructor and in the Reset method). — Victor-Philipp Negoescu, Apr 09 '17 at 12:24
This implementation is broken because it never increments `current`. — MikeB, Apr 08 '22 at 23:42

score 5 · Answer 3 · answered Aug 02 '11 at 07:29

5

You don't need to implement IEnumerable or any interface. In order to be able to use your class in a foreach, all that you need is to add an instance method to your class with the follwing signature:

IEnumerator GetEnumerator()

answered Aug 02 '11 at 07:29

nakhli

4,009
5
38
61

1

I did not know this! Saves redundant effort, as `IEnumerable` inherits from `IEnumrable` which creates an annoying mess. – Amir Abiri Jan 19 '17 at 10:19

C# - How to implement IEnumerator on a class

3 Answers3

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