Question

我在实现IComparer方法时遇到了麻烦。基本上，我想比较两个自定义对象的属性（属性是整数类型）。

dE是一个字典（Of String，customObj） prTabIndex是customObj的属性，其类型为Integer （这些适用于所有例子）

经过一些搜索，我找到了this线程，它提出了3个方面：一个List方法，利用LINQ，并使用一些C＃3.0功能。但是，在vb中，不确定他们最好的方法是什么。

我尝试了三种不同的方法：

...滚动我自己的IComparer实现：

Public m As Sub(ByRef d As Dictionary(of String, customObj))

   Dim sortedD As New SortedDictionary(Of String, customObj)(d, myCompare)

End Sub

 Public Class myCompare
     Implements IComparer

    Public Function Compare(ByVal x As Object, ByVal y As Object) As Integer Implements System.Collections.IComparer.Compare
        If TryCast(x, customObj).prTabIndex < TryCast(y, customObj).prTabIndex Then
            Return -1
        Else
            Return 1
        End If
    End Function
End Class

...对列表进行排序（我觉得这很有用 - 让这个帖子略显学术化）。

Dim sortedL As List(Of KeyValuePair(Of String, customObj)) = dE.ToList
    sortedL.Sort(Function(firstPair As KeyValuePair(Of String, customObj), nextPair As KeyValuePair(Of String, customObj)) firstPair.Value.prTabIndex.CompareTo(nextPair.Value.prTabIndex))

...或直接将lambda函数合并到SortedDictionary的转换中：

        Dim dESorted = From kvp As KeyValuePair(Of String, customObj) In dE.ToDictionary(Function(first As KeyValuePair(Of String, customObj), second As KeyValuePair(Of String, customObj)) first.Value.prTabIndex.CompareTo(nextPair.Value.prTabIndex))

请注意，VS2008已经加下划线'dE.ToDictionary ...'（到行尾）并根据我将鼠标悬停在哪里给我两条消息：

1）“扩展方法'签名'中类型参数的数据类型由于'System.Linq.Enumerable中定义的'签名不能从这些参数中推断出来。明确指定数据类型可能会纠正这个问题错误。在“ToDictionary”上空盘旋时看到。

2）嵌套函数与委托“签名”的签名不同。看到“ToDictionary”之后盘旋在任何东西上。

不可否认，我是lambda函数的新手。

Q1）每个实施中我的距离是多远？

Q2）哪一个计算最便宜？为什么呢？

Q3）哪一个在计算上最贵？为什么呢？

温暖的问候，

-sf

Answer 1

如果实现Generic IC Comparable（Of ...），则可以保存自我强制转换。我认为你也应该处理这两个对象相等的可能性。

Public Class DemoClass
  Implements IComparable(Of DemoClass)

  Private mstrField1 As String
  Public Property Field1() As String
    Get
      Return mstrField1
    End Get
    Set(ByVal value As String)
      mstrField1 = value
    End Set
  End Property


  Private mstrField2 As String
  Public Property Field2() As String
    Get
      Return mstrField2
    End Get
    Set(ByVal value As String)
      mstrField2 = value
    End Set
  End Property

  Private mstrField3 As String
  Public Property Field3() As String
    Get
      Return mstrField3
    End Get
    Set(ByVal value As String)
      mstrField3 = value
    End Set
  End Property

  ''' <summary>
  ''' Default sort - 1 ASC, 2 ASC, 3 ASC 
  ''' </summary>
  ''' <param name="other"></param>
  ''' <returns></returns>
  ''' <remarks></remarks>
  Public Function CompareTo(ByVal other As DemoClass) As Integer Implements System.IComparable(Of DemoClass).CompareTo
    '-1 = less than other; 0 = same as other; +1 = greater than other'
    Select Case Me.Field1
      Case Is < other.Field1 : Return -1
      Case Is > other.Field1 : Return 1
      Case Else 'equal
        Select Case Me.Field2
          Case Is < other.Field2 : Return -1
          Case Is > other.Field2 : Return 1
          Case Else 'equal
            Select Case Me.Field3
              Case Is < other.Field3 : Return -1
              Case Is > other.Field3 : Return 1
              Case Else : Return 0 'equal
            End Select
        End Select
    End Select
  End Function
End Class

将Dictionary转换为SortedDictionary后，为自定义对象实现iComparer

1 个答案: