C# 将 List<T> 转换为 object[]

Convert List<T> to object[]

提问by Graviton

I am looking for a one liner that transforms List<T>into object[]. It's one liner, so I am not interested in solutions such as foreach, or for...

我正在寻找一种可以转换List<T>为object[]. 这是一个衬垫，所以我对诸如foreach, 或for... 之类的解决方案不感兴趣。

Any takers?

有接班人吗？

Hint: No, both List<T>.ToArray()and List<T>.ToArray<object>()don't work.

提示：没有，都List<T>.ToArray()与List<T>.ToArray<object>()不工作。

Edit: Why List<T>.ToArray<object>()doesn't work? Because it can't compile.

编辑：为什么List<T>.ToArray<object>()不起作用？因为它无法编译。

采纳答案by Randolpho

mylist.Cast<object>().ToArray()

That will only iterate once, by the way, in case you were wondering about the performance. O(n). :)

顺便说一下，这只会迭代一次，以防您对性能感到疑惑。在）。:)

Why? Well, because Cast<object>will use deferred execution and won't actually do anything until the list is iterated by ToArray().

为什么？好吧，因为Cast<object>将使用延迟执行并且在列表由ToArray().

回答by Stefan Steinegger

theList.Cast<object>().ToArray()

or

或者

new List<object>(theList).ToArray()

回答by Mark Carpenter

If you don't mind writing a very short, reusable function, the ConvertAll Extension Method might help:

如果您不介意编写一个非常短的、可重用的函数，ConvertAll 扩展方法可能会有所帮助：

http://msdn.microsoft.com/en-us/library/73fe8cwf.aspx

http://msdn.microsoft.com/en-us/library/73fe8cwf.aspx

EDIT:

编辑：

This would work too

这也行

List<int> intList = new List<int>() { 1, 3, 4 };
object[] objectList = intList.ConvertAll(item => (object)item).ToArray();

回答by ?a?da? Tekin

List<T>.Select(x => x as object).ToArray();

Should return an object[].

应该返回一个object[].

回答by Samuel

对于 LINQ 之前的解决方案（仅适用于引用类型）。

(object[])List<T>.ToArray();

回答by stevehipwell

In C# on .NET 2.0 (VS 2008) the following compiles and doesn't use LINQ (as far as I can see) for reference types.

在 .NET 2.0 (VS 2008) 上的 C# 中，以下编译并且不使用 LINQ（据我所知）作为引用类型。

 object[] oArray;
 List<MyObject> oList = new List<MyObject>();
 oArray = oList.ToArray();

This does not require a cast as all reference types have object as their base.

这不需要强制转换，因为所有引用类型都以对象为基础。

回答by jrummell

If you don't have Linq (.Net 3.0) then you can use the ConvertAll()and ToArray()methods in List:

如果您没有 Linq (.Net 3.0)，那么您可以使用List 中的ConvertAll()和ToArray()方法：

List<T> list = new List<T>();

object[] objects = list.ConvertAll<object>(item => (object)item).ToArray();

回答by Tomer W

I'd suggest creating a ListCastAdapter,

我建议创建一个 ListCastAdapter，

Lets say you want to Convert List to List

假设您想将列表转换为列表

Create implementation of an implementation of IList that return items from a List

创建从 List 返回项目的 IList 实现的实现

most likely i call it class ListCastAdapter

很可能我称之为类 ListCastAdapter

Have a great day

祝你有美好的一天

implementation (NOT TESTED):

实施（未测试）：

Notice: It is recomended to make the list ReadOnly, for the fact, now the user can insert objects that are way up the hierarchy in the original list.

注意：建议将列表设为只读，事实上，现在用户可以在原始列表中插入层次结构更高的对象。

Note: CopyTo() is not implemented, you can create the same idea for the array.

注意： CopyTo() 没有实现，你可以为数组创建相同的想法。

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
    }
}