您可以使用Take扩展方法

var array = new byte[] {1, 2, 3, 4};
var firstTwoItems = array.Take(2);

您可以对原始数组(即IList)使用包装器，就像下面(未经测试的)代码一样。

public class SubList<T> : IList<T>
{
    #region Fields

    private readonly int startIndex;
    private readonly int endIndex;
    private readonly int count;
    private readonly IList<T> source;

    #endregion

    public SubList(IList<T> source, int startIndex, int count)
    {
        this.source = source;
        this.startIndex = startIndex;
        this.count = count;
        this.endIndex = this.startIndex + this.count - 1;
    }

    #region IList<T> Members

    public int IndexOf(T item)
    {
        if (item != null)
        {
            for (int i = this.startIndex; i <= this.endIndex; i++)
            {
                if (item.Equals(this.source[i]))
                    return i;
            }
        }
        else
        {
            for (int i = this.startIndex; i <= this.endIndex; i++)
            {
                if (this.source[i] == null)
                    return i;
            }
        }
        return -1;
    }

    public void Insert(int index, T item)
    {
        throw new NotSupportedException();
    }

    public void RemoveAt(int index)
    {
        throw new NotSupportedException();
    }

    public T this[int index]
    {
        get
        {
            if (index >= 0 && index < this.count)
                return this.source[index + this.startIndex];
            else
                throw new IndexOutOfRangeException("index");
        }
        set
        {
            if (index >= 0 && index < this.count)
                this.source[index + this.startIndex] = value;
            else
                throw new IndexOutOfRangeException("index");
        }
    }

    #endregion

    #region ICollection<T> Members

    public void Add(T item)
    {
        throw new NotSupportedException();
    }

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

    public bool Contains(T item)
    {
        return this.IndexOf(item) >= 0;
    }

    public void CopyTo(T[] array, int arrayIndex)
    {
        for (int i=0; i<this.count; i++)
        {
            array[arrayIndex + i] = this.source[i + this.startIndex];
        }
    }

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

    public bool IsReadOnly
    {
        get { return true; }
    }

    public bool Remove(T item)
    {
        throw new NotSupportedException();
    }

    #endregion

    #region IEnumerable<T> Members

    public IEnumerator<T> GetEnumerator()
    {
        for (int i = this.startIndex; i < this.endIndex; i++)
        {
            yield return this.source[i];
        }
    }

    #endregion

    #region IEnumerable Members

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

    #endregion
}

byte[] foo = new byte[4096]; 

byte[] bar = foo.Take(40).ToArray();

static byte[] SliceMe(byte[] source, int length)
{
    byte[] destfoo = new byte[length];
    Array.Copy(source, 0, destfoo, 0, length);
    return destfoo;
}

//

var myslice = SliceMe(sourcearray,41);

我在这里没有看到的另一种可能性是:Buffer.BlockCopy()比array . copy()稍微快一些，而且它还有一个额外的好处，就是能够实时地将原语数组(比如short[])转换为字节数组，这在需要通过socket传输数字数组时非常方便。

从c# 8.0/开始。Net Core 3.0

数组切片将被支持，同时添加了新的类型Index和Range。

范围结构文档 索引结构文档

Index i1 = 3;  // number 3 from beginning
Index i2 = ^4; // number 4 from end
int[] a = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
Console.WriteLine($"{a[i1]}, {a[i2]}"); // "3, 6"

var slice = a[i1..i2]; // { 3, 4, 5 }

以上代码样本摘自c# 8.0博客。

注意，^前缀表示从数组的末尾开始计数。如文档示例所示

var words = new string[]
{
                // index from start    index from end
    "The",      // 0                   ^9
    "quick",    // 1                   ^8
    "brown",    // 2                   ^7
    "fox",      // 3                   ^6
    "jumped",   // 4                   ^5
    "over",     // 5                   ^4
    "the",      // 6                   ^3
    "lazy",     // 7                   ^2
    "dog"       // 8                   ^1
};              // 9 (or words.Length) ^0

Range和Index也适用于切片数组之外，例如循环

Range range = 1..4; 
foreach (var name in names[range])

将循环1到4项

请注意，在撰写本文时，c# 8.0还没有正式发布 c# 8。. x和。net Core 3。x现已在Visual Studio 2019及以后版本中可用