vb.net – 有没有一种优雅的方式来编写这段代码？

发布时间：2020-12-17 07:27:25 所属栏目：百科来源：网络整理

导读：我继承了一些代码,当我看到它时,它让我感到畏缩.是否有更优雅的方式来写下面的内容？ Dim myItem As DTO.MyBaseClass = NothingDim myType As String = GetTypeString()Select Case myType Case Is = "Case1" myItem = Bus.BusManager(Of DTO.MyClass1).Read

我继承了一些代码,当我看到它时,它让我感到畏缩.是否有更优雅的方式来写下面的内容？

Dim myItem As DTO.MyBaseClass = Nothing
Dim myType As String = GetTypeString()
Select Case myType
  Case Is = "Case1"
    myItem = Bus.BusManager(Of DTO.MyClass1).Read()
  Case Is = "Case2"
    myItem = Bus.BusManager(Of DTO.MyClass2).Read()
'... etc etc for 30 lines

有没有办法从字符串到类类型创建一个映射,然后只有这样的行？或类似的东西？

myItem = Bus.BusManager(Of MappingDealy(myType)).Read()

解决方法

由于BusManager是Generic,因此您传入的类型为< type>必须在编译时指定.它不像您可以在运行时更改的传统参数.

从您列出的代码中不清楚BusManager实际上做了什么.如果它所做的只是创建Generic类型的实例,那么创建它的人可能并不真正理解泛型.您是否有能力重新设计BusManager的工作方式,或者您是否仅限于使用它？

正如@jmoreno所提到的,您可以使用反射从包含类型名称的字符串创建类型的实例.这是如何工作的：

Imports System.Reflection
Imports System.IO

Public Class ObjectFactory
    Private Shared Function CreateObjectFromAssembly(ByVal assembly As Assembly,ByVal typeName As String) As Object
        ' resolve the type
        Dim targetType As Type = assembly.GetType(typeName)
        If targetType Is Nothing Then
            Throw New ArgumentException("Can't load type " + typeName)
        End If

        ' get the default constructor and instantiate
        Dim types(-1) As Type
        Dim info As ConstructorInfo = targetType.GetConstructor(types)
        Dim targetObject As Object = info.Invoke(Nothing)
        If targetObject Is Nothing Then
            Throw New ArgumentException("Can't instantiate type " + typeName)
        End If

        Return targetObject
    End Function

    Public Shared Function CreateObject(ByVal typeName As String) As Object
        Return CreateObjectFromAssembly(Assembly.GetExecutingAssembly,typeName)
    End Function

    Public Shared Function CreateObject(ByVal typeName As String,ByVal assemblyFileName As String) As Object
        Dim assemblyFileInfo = New FileInfo(assemblyFileName)
        If assemblyFileInfo.Exists Then
            Return CreateObjectFromAssembly(Reflection.Assembly.LoadFrom(assemblyFileName),typeName)
        Else
            Throw New ArgumentException(assemblyFileName + " cannot be found.")
        End If
    End Function

End Class

在生产应用程序中,我可能会将所有这些方法的返回类型设置为我的基类或接口.只需确保传入完整的typeName,包括命名空间.

有了这个工厂类,那么代码的优雅版本将如下所示：

Dim myItem as DTO.MyBaseClass = ObjectFactory.CreateObject("DTO." & GetTypeString())

（编辑：李大同）

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