如何解决工厂方法模式扩展
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
是重要的。下面是 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 MasterProject
对象或单个字符串来创建 restResponse
,我该怎么做?我有几种方法可以在下面分享,但我想知道哪种方法最正确(遵循工厂方法模式)?
#1
从我看到和读到的关于工厂方法设计模式的内容来看,拥有上面示例中的 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具有字符串重载和对象重载的 CreateProject
方法:
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哪个 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的做法?
#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。不知道是不是遵循了工厂方法模式。
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。模式在情境中以它们最适合的方式使用。我只是想在这里寻找一个通用的最佳实践规则。
解决方法
我不是 Visual Basic 程序员,但我知道 .NET 的工作原理。如果它确实是一个 projectID
,那么将 String
强制转换为 String
会是一个解决方案吗?
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
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