c# - 哪个更好？数组、ArrayList 或 List（在性能和速度方面）

Question

我需要快速处理我的页面。要添加的值的计数将是动态的。

以上哪一项是首选？有正当理由的支持。

编辑：例如：

string str = "a,b,c"; //Count of the number of elements in str is not fixed
string[] arr = str.Split(',');

或者，

ArrayList al = new ArrayList();
al.Add(str.Split(','));

Answer 1

List<T>通常应该优先于ArrayList

• 值类型更快，因为它避免了装箱。
• 强类型元素

如果您希望向调用者公开的列表是不可变的，则两者都支持List<T>和ArrayList：

List<T>.AsReadOnly()
ArrayList.ReadOnly(ArrayList list);

您的问题询问在 and 之间ArrayList进行选择List<T>，但是您的示例显示了一个数组，两者都不是。

Answer 2

“不可变”集合的数组， List<T>用于可变集合。

• “不可变”集合 - 仅在创建时更改，稍后阅读。
• 可变集合 - 一直有很多变化

性能统计数据（Array vs List vs ReadonlyCollection）：

       Array                List        ReadOnlyCollection         Penalties      Method
00:00:01.3932446    00:00:01.6677450    00:00:06.2444633    1 vs  1,2  vs  4,5   Generate
00:00:00.1856069    00:00:01.0291365    00:00:02.0674881    1 vs  5,5  vs 11,1   Sum
00:00:00.4350745    00:00:00.9422126    00:00:04.5994937    1 vs  2,2  vs 10,6   BlockCopy
00:00:00.2029309    00:00:00.4272936    00:00:02.2941122    1 vs  2,1  vs 11,3   Sort

源代码：

interface IMethods<T>
{
  T Generate(int size, Func<int, int> generator);
   int Sum(T items);
   T BlockCopy(T items);
   T Sort(T items);
}

class ArrayMethods:IMethods<int[]>
{
  public int[] Generate(int size, Func<int, int> generator)
  {
    var items = new int[size];
    for (var i = 0; i < items.Length; ++i)
      items[i] = generator(i);
    return items;
  }
  public int Sum(int[] items)
  {
    int sum = 0;
    foreach (var item in items)
      sum += item;
    return sum;
  }
  public int[] BlockCopy(int[] items)
  {
    var res = new int[items.Length / 2];
    Buffer.BlockCopy(items, items.Length / 4 * sizeof(int), res, 0, res.Length * sizeof(int));
    return res;
  }
  public int[] Sort(int[] items)
  {
    var res = new int[items.Length];
    Buffer.BlockCopy(items, 0, res, 0, items.Length * sizeof(int));
    return res;
  }
}
class ListMethods : IMethods<List<int>>
{
  public List<int> Generate(int size, Func<int, int> generator)
  {
    var items = new List<int>(size);
    for (var i = 0; i < size; ++i)
      items.Add(generator(i));
    return items;
  }
  public int Sum(List<int> items)
  {
    int sum = 0;
    foreach (var item in items)
      sum += item;
    return sum;
  }
  public List<int> BlockCopy(List<int> items)
  {
    var count = items.Count / 2;
    var res = new List<int>(count);
    var start = items.Count / 4;
    for (var i = 0; i < count; ++i)
      res.Add(items[start + i]);
    return res;
  }
  public List<int> Sort(List<int> items)
  {
    var res = new List<int>(items);
    res.Sort();
    return res;
  }
}
class ReadOnlyCollectionMethods:IMethods<ReadOnlyCollection<int>>
{
  public ReadOnlyCollection<int> Generate(int size, Func<int, int> generator)
  {
    return new ReadOnlyCollection<int>(Enumerable.Range(0, size).Select(generator).ToList());
  }

  public int Sum(ReadOnlyCollection<int> items)
  {
    int sum = 0;
    foreach (var item in items)
      sum += item;
    return sum;
  }


  public ReadOnlyCollection<int> BlockCopy(ReadOnlyCollection<int> items)
  {
    return new ReadOnlyCollection<int>(items.Skip(items.Count / 4).Take(items.Count / 2).ToArray());
  }
  public ReadOnlyCollection<int> Sort(ReadOnlyCollection<int> items)
  {
    return new ReadOnlyCollection<int>(items.OrderBy(s => s).ToList());
  }
}

static class Program
{
  static Tuple<string, TimeSpan>[] CheckPerformance<T>(IMethods<T> methods) where T:class
  {
    var stats = new List<Tuple<string, TimeSpan>>();

    T source = null;
    foreach (var info in new[] 
      { 
        new {Name = "Generate", Method = new Func<T, T>(items => methods.Generate(10000000, i => i % 2 == 0 ? -i : i))}, 
        new {Name = "Sum", Method =  new Func<T, T>(items => {Console.WriteLine(methods.Sum(items));return items;})}, 
        new {Name = "BlockCopy", Method = new Func<T, T>(items => methods.BlockCopy(items))}, 
        new {Name = "Sort", Method = new Func<T, T>(items => methods.BlockCopy(items))}, 
        new {Name = "Sum", Method =  new Func<T, T>(items => {Console.WriteLine(methods.Sum(items));return items;})}, 
      }
     )
    {
      int count = 10;
      var stopwatch = new Stopwatch();
      stopwatch.Start();
      T res = null;
      for (var i = 0; i < count; ++i)
        res = info.Method(source);
      stopwatch.Stop();
      source = res;
      stats.Add(new Tuple<string, TimeSpan>(info.Name, stopwatch.Elapsed));
    }
    return stats.ToArray();
  }

  static void Main()
  {
    var arrayStats = CheckPerformance(new ArrayMethods());
    var listStats = CheckPerformance(new ListMethods());
    var rcStats = CheckPerformance(new ReadOnlyCollectionMethods());

    Console.WriteLine("       Array                List        ReadOnlyCollection         Penalties      Method");
    for(var i = 0; i < arrayStats.Length; ++i)
    {
      Console.WriteLine("{0}    {1}    {2}    1 vs {3,4:f1}  vs {4,4:f1}   {5}", arrayStats[i].Item2, listStats[i].Item2, rcStats[i].Item2, 
        listStats[i].Item2.TotalSeconds / arrayStats[i].Item2.TotalSeconds,
        rcStats[i].Item2.TotalSeconds / arrayStats[i].Item2.TotalSeconds, arrayStats[i].Item1);
    }
  }

Answer 3

List <T> 总是会比 arrayList 快。List <T>'s不必将添加到它们的值装箱。

ArrayList仅“接受”对象，这意味着虽然您可以将任何想要的对象添加到列表中，但必须将其装箱（由 CLR 隐式），然后在需要时必须再次拆箱（由您显式）价值。

编辑：这是一个不错的链接