不，不一般。使用枚举对象的一点是，枚举中的实际对象集是不知道的(预先知道，甚至根本不知道)。

我使用这样的代码，如果我有字符串列表:

((IList<string>)Table).Count

不，不一般。使用枚举对象的一点是，枚举中的实际对象集是不知道的(预先知道，甚至根本不知道)。

我在一个方法中使用了这样的方法来检查传入的IEnumberable内容

if( iEnum.Cast<Object>().Count() > 0) 
{

}

在这样的方法中:

GetDataTable(IEnumberable iEnum)
{  
    if (iEnum != null && iEnum.Cast<Object>().Count() > 0) //--- proceed further

}

IEnumerable.Count()函数的结果可能是错误的。这是一个非常简单的测试样本:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Collections;

namespace Test
{
  class Program
  {
    static void Main(string[] args)
    {
      var test = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 };
      var result = test.Split(7);
      int cnt = 0;

      foreach (IEnumerable<int> chunk in result)
      {
        cnt = chunk.Count();
        Console.WriteLine(cnt);
      }
      cnt = result.Count();
      Console.WriteLine(cnt);
      Console.ReadLine();
    }
  }

  static class LinqExt
  {
    public static IEnumerable<IEnumerable<T>> Split<T>(this IEnumerable<T> source, int chunkLength)
    {
      if (chunkLength <= 0)
        throw new ArgumentOutOfRangeException("chunkLength", "chunkLength must be greater than 0");

      IEnumerable<T> result = null;
      using (IEnumerator<T> enumerator = source.GetEnumerator())
      {
        while (enumerator.MoveNext())
        {
          result = GetChunk(enumerator, chunkLength);
          yield return result;
        }
      }
    }

    static IEnumerable<T> GetChunk<T>(IEnumerator<T> source, int chunkLength)
    {
      int x = chunkLength;
      do
        yield return source.Current;
      while (--x > 0 && source.MoveNext());
    }
  }
}

结果必须是(7,7,3,3)，但实际结果是(7,7,3,17)

这取决于。net的版本和IEnumerable对象的实现。 微软已经修复了IEnumerable。方法来检查实现，并使用ICollection。Count或ICollection< TSource >。计数，详情见这里https://connect.microsoft.com/VisualStudio/feedback/details/454130

下面是来自Ildasm for System的MSIL。核心，系统在其中。Linq驻留。

.method public hidebysig static int32  Count<TSource>(class 

[mscorlib]System.Collections.Generic.IEnumerable`1<!!TSource> source) cil managed
{
  .custom instance void System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = ( 01 00 00 00 ) 
  // Code size       85 (0x55)
  .maxstack  2
  .locals init (class [mscorlib]System.Collections.Generic.ICollection`1<!!TSource> V_0,
           class [mscorlib]System.Collections.ICollection V_1,
           int32 V_2,
           class [mscorlib]System.Collections.Generic.IEnumerator`1<!!TSource> V_3)
  IL_0000:  ldarg.0
  IL_0001:  brtrue.s   IL_000e
  IL_0003:  ldstr      "source"
  IL_0008:  call       class [mscorlib]System.Exception System.Linq.Error::ArgumentNull(string)
  IL_000d:  throw
  IL_000e:  ldarg.0
  IL_000f:  isinst     class [mscorlib]System.Collections.Generic.ICollection`1<!!TSource>
  IL_0014:  stloc.0
  IL_0015:  ldloc.0
  IL_0016:  brfalse.s  IL_001f
  IL_0018:  ldloc.0
  IL_0019:  callvirt   instance int32 class [mscorlib]System.Collections.Generic.ICollection`1<!!TSource>::get_Count()
  IL_001e:  ret
  IL_001f:  ldarg.0
  IL_0020:  isinst     [mscorlib]System.Collections.ICollection
  IL_0025:  stloc.1
  IL_0026:  ldloc.1
  IL_0027:  brfalse.s  IL_0030
  IL_0029:  ldloc.1
  IL_002a:  callvirt   instance int32 [mscorlib]System.Collections.ICollection::get_Count()
  IL_002f:  ret
  IL_0030:  ldc.i4.0
  IL_0031:  stloc.2
  IL_0032:  ldarg.0
  IL_0033:  callvirt   instance class [mscorlib]System.Collections.Generic.IEnumerator`1<!0> class [mscorlib]System.Collections.Generic.IEnumerable`1<!!TSource>::GetEnumerator()
  IL_0038:  stloc.3
  .try
  {
    IL_0039:  br.s       IL_003f
    IL_003b:  ldloc.2
    IL_003c:  ldc.i4.1
    IL_003d:  add.ovf
    IL_003e:  stloc.2
    IL_003f:  ldloc.3
    IL_0040:  callvirt   instance bool [mscorlib]System.Collections.IEnumerator::MoveNext()
    IL_0045:  brtrue.s   IL_003b
    IL_0047:  leave.s    IL_0053
  }  // end .try
  finally
  {
    IL_0049:  ldloc.3
    IL_004a:  brfalse.s  IL_0052
    IL_004c:  ldloc.3
    IL_004d:  callvirt   instance void [mscorlib]System.IDisposable::Dispose()
    IL_0052:  endfinally
  }  // end handler
  IL_0053:  ldloc.2
  IL_0054:  ret
} // end of method Enumerable::Count