Hi all,
Have question about inheriting a class that has parameters in the
constructor such as :
Public MustInherit Class MyParentClass
Public mystring As String
Public Sub New(ByVal paramstring As String)
mystring = paramstring
End Sub
End Class
When I create the subclass :
Public Class MyChildClass <-- VS warns of a Problem here
Inherits MyParentClass
Public Sub ShowString()
MsgBox(mystring )
End Sub
End Class
VS.NET is complaining I need to declare a "sub new" in the child class
because "The base class doesn't have an accessible 'Sub new' that can be
called without arguments."
I don't understand why this should be necessary, I have no intentions of
creating and instance of this child class without the proper arguments in
New, why should a redefinition of the constructor be required?
Is this a special case for the constructor or am I missing something in how
inheritance works in .net ?
Thanks for any clarification provided,
Francisco 4 2655
Inheritance does not include inheritance of constructors.
So each of your inherited classes will need to have something like:
Public Sub New(ByVal paramstring As String)
MyBase.New(para mstring)
End Sub
"Francisco Amaro" <famaro.at.abac usemedia.dot.co m> wrote in message
news:uF******** ******@tk2msftn gp13.phx.gbl... Hi all,
Have question about inheriting a class that has parameters in the constructor such as :
Public MustInherit Class MyParentClass
Public mystring As String
Public Sub New(ByVal paramstring As String) mystring = paramstring End Sub
End Class
When I create the subclass :
Public Class MyChildClass <-- VS warns of a Problem here Inherits MyParentClass
Public Sub ShowString() MsgBox(mystring ) End Sub
End Class
VS.NET is complaining I need to declare a "sub new" in the child class because "The base class doesn't have an accessible 'Sub new' that can be called without arguments."
I don't understand why this should be necessary, I have no intentions of creating and instance of this child class without the proper arguments in New, why should a redefinition of the constructor be required?
Is this a special case for the constructor or am I missing something in
how inheritance works in .net ?
Thanks for any clarification provided,
Francisco
"Francisco Amaro" <famaro.at.abac usemedia.dot.co m> schrieb Hi all,
Have question about inheriting a class that has parameters in the constructor such as :
Public MustInherit Class MyParentClass
Public mystring As String
Public Sub New(ByVal paramstring As String) mystring = paramstring End Sub
End Class
When I create the subclass :
Public Class MyChildClass <-- VS warns of a Problem here Inherits MyParentClass
Public Sub ShowString() MsgBox(mystring ) End Sub
End Class
VS.NET is complaining I need to declare a "sub new" in the child class because "The base class doesn't have an accessible 'Sub new' that can be called without arguments."
I don't understand why this should be necessary, I have no intentions of creating and instance of this child class without the proper arguments in New, why should a redefinition of the constructor be required?
The base class constructor *must* be called. Otherwise the object is not
initialized correctly.
Is this a special case for the constructor or am I missing something in how inheritance works in .net ?
Thanks for any clarification provided,
Add a constructor without arguments to the derived class that calls the base
class constructor.
--
Armin
How to quote and why: http://www.plig.net/nnq/nquote.html http://www.netmeister.org/news/learn2quote.html
"Marina" <so*****@nospam .com> wrote in message
news:O9******** ******@TK2MSFTN GP12.phx.gbl... Inheritance does not include inheritance of constructors. So each of your inherited classes will need to have something like:
Public Sub New(ByVal paramstring As String) MyBase.New(para mstring) End Sub
Thanks for the clarification marina.
Any specific reason why it was done ? Seems quite unnecessary to me. Can't
think of a reason why the constructor sub would be an exception in
inheritance.
Will the "Finalize" sub have the same behaviour?
Francisco
"Francisco Amaro" <famaro.at.abac usemedia.dot.co m> wrote in message news:uF******** ******@tk2msftn gp13.phx.gbl... Hi all,
Have question about inheriting a class that has parameters in the constructor such as :
Public MustInherit Class MyParentClass
Public mystring As String
Public Sub New(ByVal paramstring As String) mystring = paramstring End Sub
End Class
When I create the subclass :
Public Class MyChildClass <-- VS warns of a Problem here Inherits MyParentClass
Public Sub ShowString() MsgBox(mystring ) End Sub
End Class
VS.NET is complaining I need to declare a "sub new" in the child class because "The base class doesn't have an accessible 'Sub new' that can be called without arguments."
I don't understand why this should be necessary, I have no intentions of creating and instance of this child class without the proper arguments
in New, why should a redefinition of the constructor be required?
Is this a special case for the constructor or am I missing something in
how inheritance works in .net ?
Thanks for any clarification provided,
Francisco
* "Francisco Amaro" <famaro.at.abac usemedia.dot.co m> scripsit: Have question about inheriting a class that has parameters in the constructor such as :
Public MustInherit Class MyParentClass
Public mystring As String
Public Sub New(ByVal paramstring As String) mystring = paramstring End Sub
End Class
When I create the subclass :
Public Class MyChildClass <-- VS warns of a Problem here Inherits MyParentClass
Public Sub ShowString() MsgBox(mystring ) End Sub
End Class
VS.NET is complaining I need to declare a "sub new" in the child class because "The base class doesn't have an accessible 'Sub new' that can be called without arguments."
I don't understand why this should be necessary, I have no intentions of creating and instance of this child class without the proper arguments in New, why should a redefinition of the constructor be required?
Is this a special case for the constructor or am I missing something in how inheritance works in .net ?
The inherited class will need to call the base class' ctor to be
instantiated. For a parameterless ctor, that's easy. If you do not add
a ctor, VB.NET will add a parameterless ctor to your class that calls
the base class' parameterless ctor. If there is no parameterless ctor
defined in the base class, this will fail. That's why you will have to
add a ctor yourself:
\\\
Public Sub New()
MyBase.New("The Parameter")
End Sub
///
--
Herfried K. Wagner [MVP]
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