In .NET 4.5 daca avem nevoie de un dictionar care sa fie read-only este destul de simplu. Avem la dispozitie interfata IReadOnlyDictionary si implementarea acesteia. Implementarea poate sa fie gasita in namespace-ul System.Collections.Generic din 4.5.
Dictionary<int, string> dictionary = new Dictionary<int, string>();
dictionary.Add(1, "first");
dictionary.Add(2, "second");
ReadOnlyDictionary<string, int> readOnlyDictionary =
new ReadOnlyDictionary<string, int>(dictionary);
Ce este bine de stiut ca operatiile de add/edit/delete inca exista, doar ca in momentul in care acestea o sa fie apelate o sa arunce o exceptie de tip NotSupportedException.
Daca ati lucrat cu API-ul de Team Foundation, ati putut observa ca exista deja o implementare pentru acesta colecție. La fel si in API-ul de la Office 2007.
Daca nu lucram cu API-uri care au deja implementari a unui dictionar read-only, putem sa ne definim noi propia implementare. Tot ce trebuie sa facem este sa implementam interfata IDictionary
O alta varianta este sa va definiti si o interfata de tip IReadOnlyDictionary, care sa permita doar acces la date.
Mai jos puteti sa gasiti o implementare a unui ReadOnlyDictionary, implementand direct interfata IDictionary
public class ReadOnlyDictionary<TKey, TValue> : IDictionary<TKey, TValue>
{
private const string NotsupportedExceptionMessage = "This dictionary is read-only";
private readonly IDictionary<TKey, TValue> _dictionary;
public ReadOnlyDictionary(IDictionary<TKey, TValue> dictionary)
{
_dictionary = dictionary;
}
public void Add(TKey key, TValue value)
{
throw new NotSupportedException(NotsupportedExceptionMessage);
}
public bool ContainsKey(TKey key)
{
return _dictionary.ContainsKey(key);
}
public ICollection<TKey> Keys
{
get { return _dictionary.Keys; }
}
public bool TryGetValue(TKey key, out TValue value)
{
return _dictionary.TryGetValue(key, out value);
}
public bool Contains(KeyValuePair<TKey, TValue> item)
{
return _dictionary.Contains(item);
}
public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
{
_dictionary.CopyTo(array, arrayIndex);
}
public int Count
{
get { return _dictionary.Count; }
}
public bool IsReadOnly
{
get { return true; }
}
public TValue this[TKey key]
{
get
{
return _dictionary[key];
}
set
{
throw new NotSupportedException(NotsupportedExceptionMessage);
}
}
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
{
return _dictionary.GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return (_dictionary as System.Collections.IEnumerable).GetEnumerator();
}
public bool Remove(TKey key)
{
throw new NotSupportedException(NotsupportedExceptionMessage);
}
public void Add(KeyValuePair<TKey, TValue> item)
{
throw new NotSupportedException(NotsupportedExceptionMessage);
}
public void Clear()
{
throw new NotSupportedException(NotsupportedExceptionMessage);
}
public bool Remove(KeyValuePair<TKey, TValue> item)
{
throw new NotSupportedException(NotsupportedExceptionMessage);
}
public ICollection<TValue> Values
{
get { throw new NotSupportedException(NotsupportedExceptionMessage); }
}
}
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