Enumerating through a Dictionary.KeyCollection in order

Question

According to MSDN:

The order of the keys in the Dictionary.KeyCollection is unspecified

I am assuming that this is because additions to the Dictionary are placed into some sort of a hash table.

However, I would like to return the .Keys collection from a Dictionary as an IEnumerable (or perhaps as an ICollection) from a method, and enumerate through them in the order they were originally added to the Dictionary.

How best to accomplish this?

(I am using Winforms, .NET 2.0)

Answer 1

Then keep the keys separately in a List<T>. That original order no longer exists on the dictionary. The list will repeat insertion order.

Answer 2

You could use List<KeyValuePair<K,V>> in place of Dictionary<K,V> to maintain order. The problem with this of course is that it becomes harder to update the value for a key and the fact that you can have duplicate keys. But that can be handled with these extension methods

    public static void AddOrUpdate<K, V>(this List<KeyValuePair<K, V>> list, K key, V value)
    {
        var pair = list.SingleOrDefault(kvp => kvp.Key.Equals(key));
        if (!pair.Equals(null))
            list.Remove(pair);
        list.Add(new KeyValuePair<K, V>(key, value));
    }

    public static V GetValue<K, V>(this List<KeyValuePair<K, V>> list, K key)
    {
        var pair = list.SingleOrDefault(kvp => kvp.Key.Equals(key));
        if (pair.Equals(null))
            return default(V); //or throw an exception
        return pair.Value;
    }

    public static bool ContainsKey<K, V>(this List<KeyValuePair<K, V>> list, K key)
    {
        return list.Any(kvp => kvp.Key.Equals(key));
    }