工厂方法模式扩展

Question

我有一个Project 类，可以将其子类化为MasterProject 或SubProject。我正在使用工厂方法模式来创建这些类的实例。对于这个问题，只有MasterProject 很重要。以下是ProjectFactory.vb 文件：

Public MustInherit Class ProjectFactory
    Protected MustOverride Function CreateProject(restResponse As Object) As Project
    Public MustOverride Function GetProject(restResponse As Object) As Project
End Class

Public Class MasterProjectFactory
    Inherits ProjectFactory

    Protected Overrides Function CreateProject(projectID As Object) As Project
        Return New MasterProject(projectID("Project_mpBaseProjectID_c"))
    End Function

    Public Overrides Function GetProject(projectID As Object) As Project
        Dim masterProject = CreateProject(projectID)

        Return masterProject
    End Function

End Class

Public Class SubProjectFactory
    Inherits ProjectFactory

    Protected Overrides Function CreateProject(restResponse As Object) As Project
        ' Do stuff
    End Function

    Public Overrides Function GetProject(restResponse As Object) As Project
        ' Do stuff
    End Function
End Class

目前，MasterProject 是使用 restResponse 对象创建的。如果我想选择通过传递整个restResponse 对象或单个字符串来创建MasterProject，我该怎么做？我想到了几种方法，我将在下面分享，但我想知道哪种方法最正确（遵循工厂方法模式）？

#1

根据我对工厂方法设计模式的了解和了解，使用上面示例中的GetProject 方法很有用，因此我们可以在返回项目之前进行任何必要的操作。之后，我可以检查传递的变量的类型，并调用相应的CreateProject方法，该方法具有字符串重载和对象重载：

Public Class MasterProjectFactory
    Inherits ProjectFactory

    Protected Overrides Function CreateProject(projectID As Object) As Project
        Return New MasterProject(projectID("Project_mpBaseProjectID_c"))
    End Function

    Protected Overloads Function CreateProject(projectID As String) As Project
        Return New MasterProject(projectID)
    End Function

    Public Overrides Function GetProject(projectID As Object) As Project
        Dim masterProject As MasterProject

        If projectID.GetType() Is GetType(String) Then
            masterProject = CreateProject(projectID)
        Else
            masterProject = CreateProject(projectID)
        End If

        Return masterProject
    End Function
End Class

但我在这里看到的问题是我无法区分我正在调用的 CreateProject 方法。也许在 VB.NET/C# 中有一种方法可以指定这一点，但我想知道这是否是一个好习惯？

#2

对我来说更有意义的第二个选项是简单地检查传递的参数projectID（第一个代码块中的restResponse）的类型并用它构造对象。我不知道这是否遵循工厂方法模式。

Public Class MasterProjectFactory
    Inherits ProjectFactory

    Protected Overrides Function CreateProject(projectID As Object) As Project
        If projectID.GetType() Is GetType(String) Then
            Return New MasterProject(projectID)
        Else
            Return New MasterProject(projectID("Project_mpBaseProjectID_c"))
        End If
    End Function

    Public Overrides Function GetProject(projectID As Object) As Project
        Dim masterProject = CreateProject(projectID)

        Return masterProject
    End Function
End Class

我只想指出，我知道没有必要一字不差地遵循模式。模式在情境中以最适合的方式使用。我只是在这里寻找一个通用的最佳实践规则。

Answer 1

我不是 Visual Basic 程序员，但我知道 .NET 的工作原理。如果确实是String，将projectID 转换为String 是否是一种解决方案？

Public Overrides Function GetProject(projectID As Object) As Project
    Dim masterProject As MasterProject

    If projectID.GetType() Is GetType(String) Then
        masterProject = CreateProject(CType(projectID, String))
    Else
        masterProject = CreateProject(projectID)
    End If

    Return masterProject
End Function