使用具有不同返回类型的多态子类

我有两个从基类BaseParser继承的解析器类。我想在另一个Monitor类中使用任何一个类作为参数。解析器类CS600和TCH600都有两个属性，RawDataList和SummaryDataList。 CS600类的RawDataList返回一个List（的CS600Data）; TCH600 RawDataList返回一个List（TCH600Data）。 SummaryDataList在每个Parser类中返回相似的类。 CS600Data和TCH600Data从基类BaseData派生。 BaseParser还具有RawDataList（列表（的BaseData））和SummaryDataList（列表（BaseSummaryData的））使用具有不同返回类型的多态子类

Monitor类具有私有字段，_thisParser其可以是两个混凝土解析器的上方。我希望能够在Monitor类中调用并使用_thisParser的RawDataList和SummaryDataList，但是当我构造具体的Parser类时，Visual Studio指出CS600的RawDataList属性不能覆盖BaseParser的RawDataList属性，因为它们的返回值不同类型。

我认为，自CS600Data派生自BaseData（但也增加了一些自己的新属性），我可以在任何地方使用CS600Data BaseData。我误解了什么？我怎样才能正确构造这些类？

Public MustInherit Class BaseParser 

    Protected _rawDataList As List(Of RawGasData.BaseData) 
    Public MustOverride ReadOnly Property RawDataList() As List(Of RawGasData.BaseData) 

    Protected _summaryDataList As List(Of SummaryGasData.BaseSummaryData) 
    Public MustOverride ReadOnly Property SummaryDataList() As List(Of SummaryGasData.BaseSummaryData) 

    Public Event GasDataCreated(ByVal sender As Object, ByVal e As EventArgs) 

    Public Sub New() 
    End Sub 

    Public Sub New(ByVal dataFilePath As String, ByVal unit As String) 
     Load(dataFilePath, unit) 
    End Sub 

    Public Sub Load(ByVal dataFilePath As String, ByVal unit As String) 
     Dim contents = My.Computer.FileSystem.ReadAllText(dataFilePath) 
     ParseRawData(contents) 
     GenerateSummaryData(contents, unit) 
     RaiseEvent GasDataCreated(Me, EventArgs.Empty) 
    End Sub 

    Protected MustOverride Sub ParseRawData(ByVal fileContents As String) 

    Protected MustOverride Sub GenerateSummaryData(ByVal fileContents As String, ByVal unit As String) 

End Class 

Public Class CS600Parser 
    Inherits BaseParser 

    Shadows _rawDataList As List(Of RawGasData.CS600Data) 
    'Cannot override base class' RawDataList - differ by their return types 
    Public Overrides ReadOnly Property RawDataList() As List(Of RawGasData.CS600Data) 
     Get 
      Return _rawDataList 
     End Get 
    End Property 

    Shadows _summaryDataList As List(Of SummaryGasData.CS600SummaryData) 
    'Cannot override base class' SummaryDataList - differ by their return types 
    Public Overrides ReadOnly Property SummaryDataList() As List(Of SummaryGasData.CS600SummaryData) 
     Get 
      Return _summaryDataList 
     End Get 
    End Property 

    Protected Overrides Sub ParseRawData(ByVal fileContents As String) 
     Dim data = From d In fileContents.Trim.Split(CChar(vbCrLf)) _ 
        Let fields = d.Split(","c).Select(Function(s) s.Trim) _ 
        Select New RawGasData.CS600Data With { _ 
         .SampleNumber = fields(0), _ 
         .UserID = fields(1), _ 
         .CarbonValue = CDbl(fields(2)), _ 
         .SulfurValue = CDbl(fields(3))} 

     _rawDataList = data.ToList 

    End Sub 

    Protected Overrides Sub GenerateSummaryData(ByVal fileContents As String, ByVal unit As String) 
     Dim groupedData = From d In _rawDataList _ 
          Group By d.SampleNumber Into Group _ 
          Select New SummaryGasData.CS600SummaryData With { _ 
          .DataTimeStamp = Now, _ 
          .SampleNumber = SampleNumber, _ 
          .UserID = Group.First.UserID, _ 
          .CarbonAverage = Group.Select(Function(s) s.CarbonValue).Average, _ 
          .CarbonUnit = unit, _ 
          .SulfurAverage = Group.Select(Function(s) s.SulfurValue).Average, _ 
          .SulfurUnit = unit} 

     _summaryDataList = groupedData.ToList 

    End Sub 

End Class 

Public Class TCHParser 
    Inherits BaseParser 

    Shadows _rawDataList As List(Of RawGasData.TCH600Data) 
    'Cannot override base class' RawDataList - differ by their return types 
    Public Overrides ReadOnly Property RawDataList() As List(Of RawGasData.TCH600Data) 
     Get 
      Return _rawDataList 
     End Get 
    End Property 

    Shadows _summaryDataList As List(Of SummaryGasData.TCH600SummaryData) 
    'Cannot override base class' SummaryDataList - differ by their return types 
    Public Overrides ReadOnly Property SummaryDataList() As List(Of SummaryGasData.TCH600SummaryData) 
     Get 
      Return _summaryDataList 
     End Get 
    End Property 

    Protected Overrides Sub ParseRawData(ByVal fileContents As String) 
     Dim data = From d In fileContents.Trim.Split(CChar(vbCrLf)) _ 
     Let fields = d.Split(","c).Select(Function(s) s.Trim) _ 
     Select New RawGasData.TCH600Data With { _ 
      .SampleNumber = fields(0), _ 
      .UserID = fields(1), _ 
      .OxygenValue = CDbl(fields(2)), _ 
      .NitrogenValue = CDbl(fields(3)), _ 
      .HydrogenValue = CDbl(fields(4)), _ 
      .MassUsed = CDbl(fields(5))} 

     _rawDataList = data.ToList 

    End Sub 

    Protected Overrides Sub GenerateSummaryData(ByVal fileContents As String, ByVal unit As String) 
     Dim groupedData = From d In _rawDataList _ 
          Group By d.SampleNumber Into Group _ 
          Select New SummaryGasData.TCH600SummaryData With { _ 
          .DataTimeStamp = Now, _ 
          .SampleNumber = SampleNumber, _ 
          .UserID = Group.First.UserID, _ 
          .OxygenAverage = Group.Select(Function(s) s.OxygenValue).Average, _ 
          .OxygenUnit = unit, _ 
          .NitrogenAverage = Group.Select(Function(s) s.NitrogenValue).Average, _ 
          .NitrogenUnit = unit, _ 
          .HydrogenAverage = Group.Select(Function(s) s.HydrogenValue).Average, _ 
          .HydrogenUnit = unit} 

     _summaryDataList = groupedData.ToList 
    End Sub 


End Class 


Public MustInherit Class BaseData 
    Implements IGasData 

    Private _massUsed As Double 
    Public Property MassUsed() As Double Implements IGasData.MassUsed 
     Get 
      Return _massUsed 
     End Get 
     Set(ByVal value As Double) 
      _massUsed = value 
     End Set 
    End Property 

    Private _sampleNumber As String 
    Public Property SampleNumber() As String Implements IGasData.SampleNumber 
     Get 
      Return _sampleNumber 
     End Get 
     Set(ByVal value As String) 
      _sampleNumber = value 
     End Set 
    End Property 

    Private _userID As String 
    Public Property UserID() As String Implements IGasData.UserID 
     Get 
      Return _userID 
     End Get 
     Set(ByVal value As String) 
      _userID = value 
     End Set 
    End Property 
End Class 

Public Class CS600Data 
    Inherits BaseData 


    Private _carbonValue As Double 
    Public Property CarbonValue() As Double 
     Get 
      Return _carbonValue 
     End Get 
     Set(ByVal value As Double) 
      _carbonValue = value 
     End Set 
    End Property 


    Private _sulfurValue As Double 
    Public Property SulfurValue() As Double 
     Get 
      Return _sulfurValue 
     End Get 
     Set(ByVal value As Double) 
      _sulfurValue = value 
     End Set 
    End Property 

End Class 

Public Class TCH600Data 
    Inherits BaseData 

    Private _oxygenValue As Double 
    Public Property OxygenValue() As Double 
     Get 
      Return _oxygenValue 
     End Get 
     Set(ByVal value As Double) 
      _oxygenValue = value 
     End Set 
    End Property 


    Private _nitrogenValue As Double 
    Public Property NitrogenValue() As Double 
     Get 
      Return _nitrogenValue 
     End Get 
     Set(ByVal value As Double) 
      _nitrogenValue = value 
     End Set 
    End Property 


    Private _hydrogenValue As Double 
    Public Property HydrogenValue() As Double 
     Get 
      Return _hydrogenValue 
     End Get 
     Set(ByVal value As Double) 
      _hydrogenValue = value 
     End Set 
    End Property 

End Class

来源

2012-04-10 blueshift

你应该用适当的语言（VB？）标记问题，而不是用'visual-studio'，除非问题实际上处理VS.你还应该发布你的课程代码，并指出你有问题的地方。 – 2012-04-10 00:57:57

谢谢，@KendallFrey;我进行了建议的更改 – blueshift 2012-04-10 10:30:55

你重写列表属性，如RawDataList，应该是抽象基类的类型（或更好，但IGasData），而不是派生类的多态性工作。如果您发现使BaseData或IGasData类型的列表出现问题，您可能需要检查您的设计是否符合Liskov Substitution Principle。

的简化图示，其编译和运行得很好（VB.Net 2010）：

Sub Main  
    Dim parser As BaseParser = New TCHParser() 
    Console.WriteLine(parser) 
End Sub 

Public MustInherit Class BaseData  
    Public Property SampleNumber() As String 
End Class 

Public Class TCH600Data 
    Inherits BaseData 

    Public Property OxygenValue() As Double 
End Class 

Public MustInherit Class BaseParser 
    Public MustOverride ReadOnly Property RawDataList As List(of BaseData) 
End Class

TCHParser作品就好重写RawDataList属性。另外，我不确定为什么抽象基类有一个Protected _rawDataList字段。删除它，你不必担心在派生类型中映射该字段。

Public Class TCHParser 
    Inherits BaseParser 

    ' Populate the list just so we can test easily. 
    Public Sub New() 
     Dim data As New List(Of BaseData) 
     data.Add(New TCH600Data With { 
      .SampleNumber = "1", _ 
      .OxygenValue = 1.5d }) 

     data.Add(New TCH600Data With { 
      .SampleNumber = "2", _ 
      .OxygenValue = 2.5d }) 

     _rawDataList = data 
    End Sub 

    Private _rawDataList As List(of BaseData) 
    Public Overrides ReadOnly Property RawDataList As List(of BaseData) 
     Get 
      Return _rawDataList 
     End Get 
    End Property 
End Class

来源

2012-04-10 02:10:05 Matt

谢谢，@Matt，但它不能解决返回类型问题。我将重新访问LSP以查看我缺少的内容。 – blueshift 2012-04-10 15:40:23

@blueshift，我已经更新了我的示例以更完整。 – Matt 2012-04-10 18:52:55

非常好！谢谢，@Matt;这真的解释了如何解决这个问题。 – blueshift 2012-04-11 16:54:11

使用具有不同返回类型的多态子类

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