Vb.net SortedDictionary键和值在某些地方有数组方法，但在其他地方没有

我正在尝试对结构的

SortedDictionary

进行线性插值计算，如下所示：-

主程序

Imports Measurements.Measurements

Public Class Form1

Private Sub Button1_Click( sender As System.Object,  e As System.EventArgs) Handles Button1.Click

    Dim mydic As SortedDictionary(Of Distance, Temperature) =
                        New SortedDictionary(Of Distance, Temperature)
    mydic.Add(Distance.FromMetres(20), Temperature.FromCentigrade(30))
    mydic.Add(Distance.FromMetres(0), Temperature.FromCentigrade(10))

    Dim dicinterpolated_temperature As Temperature = DicInterpolate
                                                       (Distance.FromMetres(7),
                                                        mydic)
End Sub

Public Function DicInterpolate (Of YType As {Structure, IMeasurements}, _
                                   XType As {Structure, IMeasurements}) _
                  (ByVal x_value           As XType,
                   ByVal sorted_dictionary As SortedDictionary(Of XType, YType)) _
         As YType
            Return Interpolate (x_value,
                                sorted_dictionary.Keys.ToArray,
                                sorted_dictionary.Values.ToArray)
End Function

End Class

其中，

Distance

和

Temperature

是实现

i可比较

和

i测量

等功能的结构，并在

测量

命名空间中定义。此调用调用

度量

项目中的函数，因此

Imports System.Collections.Generic

Namespace Measurements

    Public Module Interpolation

        Public Function Interpolate (Of YType As {Structure, IMeasurements}, _
                                        XType As {Structure, IMeasurements}) _
                                    (ByVal x3 As XType,
                                     ByVal x_values() As XType, _
                                     ByVal y_values() As YType) _
                                     As YType
            ' calculate the answer and return it.
        End Function

    End Module

End Namespace

到目前为止，一切顺利。这一切都很好。但是，当我试图将DicInterpolate函数推送到它真正所属的度量名称空间时，我在这一行得到了编译错误：-

Return Interpolate (x_value,
                    sorted_dictionary.Keys.ToArray,
                    sorted_dictionary.Values.ToArray)

报告的错误有：-

'ToArray' is not a member of System.Collections.Generic.SortedDictionary(Of XType, YType).KeyCollection
'ToArray' is not a member of System.Collections.Generic.SortedDictionary(Of XType, YType).ValueCollection

有人知道为什么会这样，我能做些什么吗？

是属于

System.Linq

命名空间的扩展方法。因此，您必须添加引用并在全局（在项目设置中）或VB文件顶部添加

Imports System.Linq