Read-only generic dictionary

ReadOnlyDictionary.cs

public class ReadOnlyDictionary<TKey, TValue> : IDictionary<TKey, TValue>
{
    private readonly IDictionary<TKey, TValue> dictionary;

    public ReadOnlyDictionary()
    {
        this.dictionary = new Dictionary<TKey, TValue>();
    }

    public ReadOnlyDictionary(IDictionary<TKey, TValue> dictionary)
    {
        this.dictionary = dictionary;
    }

    public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
    {
        return this.dictionary.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return this.dictionary.GetEnumerator();
    }

    public void Add(KeyValuePair<TKey, TValue> item)
    {
        throw new NotSupportedException();
    }

    public void Clear()
    {
        throw new NotSupportedException();
    }

    public bool Contains(KeyValuePair<TKey, TValue> item)
    {
        return this.dictionary.Contains(item);
    }

    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
    {
        this.dictionary.CopyTo(array, arrayIndex);
    }

    public bool Remove(KeyValuePair<TKey, TValue> item)
    {
        throw new NotSupportedException();
    }

    public int Count
    {
        get { return this.dictionary.Count; }
    }

    public bool IsReadOnly
    {
        get { return true; }
    }

    public bool ContainsKey(TKey key)
    {
        return this.dictionary.ContainsKey(key);
    }

    public void Add(TKey key, TValue value)
    {
        throw new NotSupportedException();
    }

    public bool Remove(TKey key)
    {
        throw new NotSupportedException();
    }

    public bool TryGetValue(TKey key, out TValue value)
    {
        return this.dictionary.TryGetValue(key, out value);
    }

    public TValue this[TKey key]
    {
        get { return this.dictionary[key]; }
        set { throw new NotSupportedException(); }
    }

    public ICollection<TKey> Keys
    {
        get { return this.dictionary.Keys; }
    }

    public ICollection<TValue> Values
    {
        get { return this.dictionary.Values; }
    }
}