无法将类型为"<> d__6"的对象强制转换为"System.Object []"

Question

我正在尝试延迟加载(带有yield返回的扩展)2D对象数组中的行.我收到以下错误:

c#无法将类型为"<> d__6"的对象强制转换为"System.Object []".

在该Parse方法中找到的此行上发生异常:

yield return (TSource) conversion(o);

我不明白为什么C#认为返回值<>d__6代替Object[].我通常编程,VB.NET所以我不认为我理解的细微差别C#.我究竟做错了什么？我看了其他类似的问题/答案,但仍然感到困惑.

public static IEnumerable<TSource> Parse<TSource>(this object[,] array
        , Func<IEnumerable<object[]>, IEnumerable<TSource>> conversion
        , int rowStart, int columnStart, int rowCount, int columnCount)
    {

        IEnumerable<object[]> o 
            = array.ForEachRow(rowStart, columnStart, rowCount, columnCount);

        yield return (TSource) conversion(o);

    }

ForEachRow方法:

    public static IEnumerable<object[]> ForEachRow(this object[,] array, 
               int rowStart, int columnStart, int rowCount, int columnCount)
    {

        object[] array1d=new object[columnCount];
        for (int row = rowStart; row < rowCount; row++)
        {
            for (int column = columnStart; column < columnCount; column++)
            {
                array1d[column] = array[row, column];
            }
            yield return (object[]) array1d;
        }
    }

我知道之前已经问过这个问题,但遗憾的是其他答案对我来说没有意义(我主要用VB编程).

您可以用来编译和测试的代码(In VB.NET):

基本上我从Excel获得一个2D对象数组,并希望将它放在一个类中并使用Linq进行评估.

 Dim oData As Object(,) = {{"OrderDate", "Region", "Rep", "Item", "Units", "Unit Cost", "Total"} _
        , {New DateTime(2011, 1, 6), "East", "Jones", "Pencil", 95, 1.99, 189.05} _
        , {New DateTime(2011, 1, 23), "Central", "Kivell", "Binder", 50, 19.99, 999.5} _
        , {New DateTime(2011, 2, 9), "Central", "Jardine", "Pencil", 36, 4.99, 179.64} _
        , {New DateTime(2011, 2, 26), "Central", "Gill", "Pen", 27, 19.99, 539.73} _
        , {New DateTime(2011, 3, 15), "West", "Sorvino", "Pencil", 56, 2.99, 167.44} _
        }

    Dim clsSales = oData.Parse(Of SaleOrder)(Function(o As Object()) New SaleOrder( _
                                         If(IsDate(o(0)), o(0), #1/1/1900#) _
                                         , o(1).ToString _
                                         , o(2).ToString _
                                         , o(3).ToString _
                                         , If(IsNumeric(o(4)), CInt(o(4)), 0) _
                                         , If(IsNumeric(o(5)), o(5), 0) _
                                         ), 1, 0, oData.GetUpperBound(0), 6)

    For Each cls In clsSales
        Console.WriteLine(cls.ToString)
    Next

课程在哪里:

 Class SaleOrder

Public Sub New(ByVal date_ As Date, ByVal region_ As String, ByVal rep As String, ByVal item_ As String, ByVal units As Integer _
               , ByVal cost As Double)

    OrderDate = date_
    Region = region_
    Representative = rep
    Item = item_
    UnitCount = units
    UnitCost = cost

End Sub

Public OrderDate As DateTime
Public Region As String
Public Representative As String
Public Item As String
Public UnitCount As Integer = 5
Public UnitCost As Double
Public ReadOnly Property Total() As Double
    Get
        Return UnitCount * UnitCost
    End Get
End Property

Public Overrides Function ToString() As String
    Return String.Format("{0} {1} {2} {3} {4} {5} {6}", OrderDate, Region, Representative, Item, UnitCount, UnitCost, Total)
End Function

End Class

最终解决方案

    public static IEnumerable<TSource> Parse<TSource>(this object[,] array
        , Func<object[], TSource> conversion
        , int rowStart, int columnStart, int rowCount, int columnCount)
    {

        for (int row = rowStart; row < rowCount; row++)
        {
            object[] array1d = new object[columnCount];
            for (int column = columnStart; column < columnCount; column++)
            {
                array1d[column] = array[row, column];
            }
            yield return conversion(array1d);
        }

    }

Answer 1

通过评论中的所有信息,现在可以清楚地了解这里发生了什么.让我们做一个更简单的复制:

public static IEnumerable<Tiger> Parse()
{
  object obj = ForEachRow();
  yield return (Tiger) obj;
}

public static IEnumerable<Tiger> ForEachRow()
{
  yield return new Tiger();
}

好的,编译器对底部方法做了什么？它重写如下:

class ForEachRowEnumerable : IEnumerable<Tiger>
{
    ... a class which implements an IEnumerable<Tiger> 
    that yields a single tiger...
}

public static IEnumerable<Tiger> ForEachRow()
{
  return new ForEachRowEnumerable();
}

那么现在第一种方法是做什么的呢？

你打电话给ForEachRow.这将返回一个新的ForEachRowEnumerable.您将其转换为对象.然后,您将对象转换为Tiger.但ForEachRowEnumerable不是老虎; 这是一个会给你一系列老虎的课程.因此运行时会给出错误"无法将ForEachRowEnumerable强制转换为Tiger".

C#编译器当然没有将该类命名为"ForEachRowEnumerable".它命名它<>d__6以确保您不可能按名称实际使用该类.