我最近和vb.net一起工作并且遇到了一个带有泛型的工厂模式问题。尽管我已经解决了它,但我不知道它为什么在vb.net中不起作用。我有几年的C#经验,我有时会在c#中编写如下代码,并且没有任何问题。在c#中使用泛型的工厂模式工作,但在vb.net中不起作用,为什么?
public class GenericTest
{
public static void Test()
{
var test = Factory<TestItem>.GetTest(ProcessType.Derived);
test.Do();
}
}
public class TestItem
{
public int Property1 { get; set; }
}
public class TestBase<T> where T: class
{
public virtual void Do()
{
Console.WriteLine(typeof(T).ToString());
}
}
public class TestDerived : TestBase<TestItem>
{
public override void Do()
{
Console.WriteLine(typeof(TestItem).ToString());
}
}
public class Factory<T> where T:class
{
public static TestBase<T> GetTest(ProcessType processType)
{
switch (processType)
{
case ProcessType.Derived :
return new TestDerived() as TestBase<T>;
default:
return new TestBase<T>();
}
}
}
public enum ProcessType
{
Base,
Derived
}
但是当我将上面的代码移植到vb.net时,编译器给了我一个错误。
Public Class GenericTest
Public Shared Sub Test()
Dim test = Factory(Of TestItem).GetTest(ProcessType.Derived)
test.DoIt()
End Sub
End Class
Public Class TestItem
Public Property Property1 As Integer
End Class
Public Class TestBase(Of T As Class)
Public Overridable Sub DoIt()
Console.WriteLine(GetType(T).ToString())
End Sub
End Class
Public Class TestDerived
Inherits TestBase(Of TestItem)
Public Overloads Sub DoIt()
Console.WriteLine(GetType(TestItem).ToString())
End Sub
End Class
Public Class Factory(Of T As Class)
Public Shared Function GetTest(processType As ProcessType) As TestBase(Of T)
Select Case processType
Case VB_Sandbox.ProcessType.Derived
' This line gives me a compile error saying 'cannot convert TestDerived to TestBase(Of T)'
Return DirectCast(New TestDerived(), TestBase(Of T))
Case Else
Return New TestBase(Of T)
End Select
End Function
End Class
Public Enum ProcessType
Base
Derived
End Enum
因此,我介绍了下面的界面,使一切正常,这实际上解决了我的问题。
Public Class TestBase(Of T As Class)
Implements ITest
Public Overridable Sub DoIt() Implements ITest.DoIt
Console.WriteLine(GetType(T).ToString())
End Sub
End Class
Public Class TestDerived
Inherits TestBase(Of TestItem)
Public Overloads Sub DoIt()
Console.WriteLine(GetType(TestItem).ToString())
End Sub
End Class
Public Class Factory(Of T As Class)
Public Shared Function GetTest(processType As ProcessType) As ITest
Select Case processType
Case VB_Sandbox.ProcessType.Derived
Return DirectCast(New TestDerived(), ITest)
Case Else
Return New TestBase(Of T)
End Select
End Function
End Class
Public Interface ITest
Sub DoIt()
End Interface
这只是vb.net的限制吗?
好吧,我知道了。为什么TestDerived需要从TestBase继承的主要原因是在实际的代码每个派生类希望把重点放在了每个具体类做一些独特的作品,所以我花了一段日子要怎么解决。无论如何,你帮助我了解发生了什么。谢谢dlev。 –