Question

我发现自己经常调用lambdas中的函数，因为提供的委托不匹配或没有足够的参数。令人恼火的是我不能在子程序上做lambda。每次我想要这样做时，我必须将我的子程序包装在一个不返回任何内容的函数中。不漂亮，但它的工作原理。

还有另一种方法可以让这更顺畅/更漂亮吗？

我已经读过，整个lambda的不足可能会在VS2010 / VB10中修复，所以我的问题更多是出于好奇。

一个简单的例子：

Public Class ProcessingClass
    Public Delegate Sub ProcessData(ByVal index As Integer)
    Public Function ProcessList(ByVal processData As ProcessData)
        ' for each in some list processData(index) or whatever'
    End Function
End Class

Public Class Main

    Private Sub ProcessingSub(ByVal index As Integer, _
                              ByRef result As Integer)
        ' (...) My custom processing '
    End Sub

    Private Function ProcessingFunction(ByVal index As Integer, _
                                        ByRef result As Integer) As Object
        ProcessingSub(index, result)
        Return Nothing
    End Function

    Public Sub Main()
        Dim processingClass As New ProcessingClass
        Dim result As Integer
        ' The following throws a compiler error as '
        ' ProcessingSub does not produce a value'
        processingClass.ProcessList( _
            Function(index As Integer) ProcessingSub(index, result))
        ' The following is the workaround that'
        ' I find myself using too frequently.'
        processingClass.ProcessList( _
            Function(index As Integer) ProcessingFunction(index, result))
    End Sub

End Class

Answer 1

如果您发现自己经常使用相同类型的数据，则可以将该委托包装在一个类中。

创建一个转换为委托的基类：

Public MustInherit Class ProcessDataBase
    Public Shared Widening Operator CType(operand As ProcessDataBase) as ProcessingClass.ProcessData
        Return AddressOf operand.Process
    End Sub

    Protected MustOverride Sub Process(index As Integer)  
End Class

继承自班级：

Public Class ProcessResult
    Inherits ProcessDataBase

    Public Result As Integer

    Protected Overrides Sub Process(index as Integer)
        ' Your processing, result is modified.
    End SUb
End Class

使用它：

Public Class Main()
    Public Sub Main()
        Dim processingClass As New ProcessingClass
        Dim processor As New ProcessResult

        processingClass.ProcessList(processor)
        Dim result as integer=processor.Result
    End Sub
End Class

Answer 2

它在VB10中已修复，VS10 Beta为available，如果您可以选择使用它。在VB10中，你有没有返回值的lambdas，以及内联子/函数。

现在，也许你可以忘记lambdas并与代表合作？类似的东西：

processingClass.ProcessList(AddressOf ProcessingSub)

在vb.net中调用lambda中的子例程

2 个答案: