Я ищу один вкладыш, который преобразует List<T> в object[]. Это один лайнер, поэтому меня не интересуют такие решения, как foreach или for...
Любые участники?
Подсказка: Нет, оба List<T>.ToArray() и List<T>.ToArray<object>() не работают.
Изменить: Почему List<T>.ToArray<object>() не работает? Потому что он не может скомпилировать.
mylist.Cast<object>().ToArray()
Это будет только повторять один раз, кстати, на случай, если вам интересно о производительности. На).:)
Почему? Ну, потому что Cast<object> будет использовать отложенное выполнение и фактически ничего не сделает, пока список не будет повторен с помощью ToArray().
List<T>.Select(x => x as object).ToArray();
Должен возвращать object[].
Если у вас нет Linq (.Net 3.0), вы можете использовать ConvertAll() и ToArray() в списке:
List<T> list = new List<T>();
object[] objects = list.ConvertAll<object>(item => (object)item).ToArray();
theList.Cast<object>().ToArray()
или
new List<object>(theList).ToArray()
(object[])List<T>.ToArray();
Если вы не возражаете писать очень короткую функцию многократного использования, метод расширения ConvertAll может помочь:
http://msdn.microsoft.com/en-us/library/73fe8cwf.aspx
EDIT:
Это тоже сработает
List<int> intList = new List<int>() { 1, 3, 4 };
object[] objectList = intList.ConvertAll(item => (object)item).ToArray();
В С# на .NET 2.0 (VS 2008) следующий компилирует и не использует LINQ (насколько я могу видеть) для ссылочных типов.
object[] oArray;
List<MyObject> oList = new List<MyObject>();
oArray = oList.ToArray();
Это не требует приведения, так как все ссылочные типы имеют объект в качестве базы.
Я бы предложил создать ListCastAdapter,
Предположим, вы хотите преобразовать список в список
Создать реализацию реализация IList, которая возвращает элементы из списка
Скорее всего, я назову его классом ListCastAdapter
Отличный день
Уведомление: рекомендуется сделать список ReadOnly, для того факта, теперь пользователь может вставлять объекты, которые находятся вверх по иерархии в оригинале список.
Примечание: CopyTo() не реализовано, вы можете создать ту же идею для массива.
using System.Collections;
using System.Collections.Generic;
namespace UDF.MyDataLayer
{
internal class ListCastAdapter<S,T> : IList<T> where T : class where S : class
{
private List<S> adaptee;
public ListCastAdapter(List<S> adaptee )
{
this.adaptee = adaptee;
}
#region Implementation of IEnumerable
public class EnumeratorCastAdapter : IEnumerator<T>
{
private IEnumerator<S> adaptee;
public EnumeratorCastAdapter(IEnumerator<S> adaptee)
{
this.adaptee = adaptee;
}
#region Implementation of IDisposable
/// <summary>
/// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
/// </summary>
/// <filterpriority>2</filterpriority>
public void Dispose()
{
adaptee.Dispose();
}
#endregion
#region Implementation of IEnumerator
/// <summary>
/// Advances the enumerator to the next element of the collection.
/// </summary>
/// <returns>
/// true if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the collection.
/// </returns>
/// <exception cref="T:System.InvalidOperationException">The collection was modified after the enumerator was created. </exception><filterpriority>2</filterpriority>
public bool MoveNext()
{
return adaptee.MoveNext();
}
/// <summary>
/// Sets the enumerator to its initial position, which is before the first element in the collection.
/// </summary>
/// <exception cref="T:System.InvalidOperationException">The collection was modified after the enumerator was created. </exception><filterpriority>2</filterpriority>
public void Reset()
{
adaptee.Reset();
}
/// <summary>
/// Gets the element in the collection at the current position of the enumerator.
/// </summary>
/// <returns>
/// The element in the collection at the current position of the enumerator.
/// </returns>
public T Current
{
get
{
// needs to check if it is an Object or Value Type
return adaptee.Current as T;
}
}
/// <summary>
/// Gets the current element in the collection.
/// </summary>
/// <returns>
/// The current element in the collection.
/// </returns>
/// <exception cref="T:System.InvalidOperationException">The enumerator is positioned before the first element of the collection or after the last element.</exception><filterpriority>2</filterpriority>
object IEnumerator.Current
{
get { return Current; }
}
#endregion
}
/// <summary>
/// Returns an enumerator that iterates through the collection.
/// </summary>
/// <returns>
/// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
/// </returns>
/// <filterpriority>1</filterpriority>
public IEnumerator<T> GetEnumerator()
{
return new EnumeratorCastAdapter(adaptee.GetEnumerator());
}
/// <summary>
/// Returns an enumerator that iterates through a collection.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
/// </returns>
/// <filterpriority>2</filterpriority>
IEnumerator IEnumerable.GetEnumerator()
{
return adaptee.GetEnumerator();
}
#endregion
#region Implementation of ICollection<T>
/// <summary>
/// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.</exception>
public void Add(T item)
{
adaptee.Add(item as S);
}
/// <summary>
/// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only. </exception>
public void Clear()
{
adaptee.Clear();
}
/// <summary>
/// Determines whether the <see cref="T:System.Collections.Generic.ICollection`1"/> contains a specific value.
/// </summary>
/// <returns>
/// true if <paramref name="item"/> is found in the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false.
/// </returns>
/// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
public bool Contains(T item)
{
return adaptee.Contains(item as S);
}
/// <summary>
/// Copies the elements of the <see cref="T:System.Collections.Generic.ICollection`1"/> to an <see cref="T:System.Array"/>, starting at a particular <see cref="T:System.Array"/> index.
/// </summary>
/// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from <see cref="T:System.Collections.Generic.ICollection`1"/>. The <see cref="T:System.Array"/> must have zero-based indexing.</param><param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.</param><exception cref="T:System.ArgumentNullException"><paramref name="array"/> is null.</exception><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="arrayIndex"/> is less than 0.</exception><exception cref="T:System.ArgumentException"><paramref name="array"/> is multidimensional.-or-The number of elements in the source <see cref="T:System.Collections.Generic.ICollection`1"/> is greater than the available space from <paramref name="arrayIndex"/> to the end of the destination <paramref name="array"/>.-or-Type <paramref name="T"/> cannot be cast automatically to the type of the destination <paramref name="array"/>.</exception>
public void CopyTo(T[] array, int arrayIndex)
{
throw new System.NotImplementedException("Not Needed by Me, implement ArrayCastAdapter if needed");
}
/// <summary>
/// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <returns>
/// true if <paramref name="item"/> was successfully removed from the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false. This method also returns false if <paramref name="item"/> is not found in the original <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </returns>
/// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.</exception>
public bool Remove(T item)
{
adaptee.Remove(item as S);
}
/// <summary>
/// Gets the number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <returns>
/// The number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </returns>
public int Count
{
get { return adaptee.Count; }
}
/// <summary>
/// Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </summary>
/// <returns>
/// true if the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only; otherwise, false.
/// </returns>
public bool IsReadOnly
{
get
{
return true; // change, to live on the edge
}
}
#endregion
#region Implementation of IList<T>
/// <summary>
/// Determines the index of a specific item in the <see cref="T:System.Collections.Generic.IList`1"/>.
/// </summary>
/// <returns>
/// The index of <paramref name="item"/> if found in the list; otherwise, -1.
/// </returns>
/// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.IList`1"/>.</param>
public int IndexOf(T item)
{
return adaptee.IndexOf(item as S);
}
/// <summary>
/// Inserts an item to the <see cref="T:System.Collections.Generic.IList`1"/> at the specified index.
/// </summary>
/// <param name="index">The zero-based index at which <paramref name="item"/> should be inserted.</param><param name="item">The object to insert into the <see cref="T:System.Collections.Generic.IList`1"/>.</param><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="index"/> is not a valid index in the <see cref="T:System.Collections.Generic.IList`1"/>.</exception><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IList`1"/> is read-only.</exception>
public void Insert(int index, T item)
{
adaptee.Insert(index, item as S);
}
/// <summary>
/// Removes the <see cref="T:System.Collections.Generic.IList`1"/> item at the specified index.
/// </summary>
/// <param name="index">The zero-based index of the item to remove.</param><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="index"/> is not a valid index in the <see cref="T:System.Collections.Generic.IList`1"/>.</exception><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IList`1"/> is read-only.</exception>
public void RemoveAt(int index)
{
adaptee.RemoveAt(index);
}
/// <summary>
/// Gets or sets the element at the specified index.
/// </summary>
/// <returns>
/// The element at the specified index.
/// </returns>
/// <param name="index">The zero-based index of the element to get or set.</param><exception cref="T:System.ArgumentOutOfRangeException"><paramref name="index"/> is not a valid index in the <see cref="T:System.Collections.Generic.IList`1"/>.</exception><exception cref="T:System.NotSupportedException">The property is set and the <see cref="T:System.Collections.Generic.IList`1"/> is read-only.</exception>
public T this[int index]
{
get { return adaptee[index] as T; }
set { adaptee[index] = value as S; }
}
#endregion
}
}