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I'm a c# developer and have not enought experience in VB.NET.
the scenario:
Namespace Presenters
Public Class BaseFooPresenter
' assuming the public default parameterless constructor
Public Sub New(ByVal strvar As String)
' TODO with strvar variabile
End Sub
End Class
Public Class FooPresenter
Inherits BaseFooPresenter
Public Sub New(ByVal boolvar As Boolean)
' TODO with boolvar variabile
End Sub
Public Sub New(ByVal boolvar As Boolean, _
ByVal objvar As Object)
MyBase.New(String.Empty)
Me.New(true)
' TODO with objvar variabile
End Sub
End Class
End Namespace
With this code at the second FooPresenter constructor i get an error
"Constructor call is valid only at the first statement in an instance constructor."
at:
Me.New(true)
If i invert the order i get the error at:
MyBase.New(String.Empty)
I can create a method SetValues( ... parameters ... ) and call it from the two constructors but does someone knwos a workaround to avoid this error?, why the compiler do not validate the possibility to call the base constructor before the overloaded constructor?.
Does someone knows how to justify logically the fact that it's not possible to call the base class constructor and another class level constructor from one class level constructor at the same time?
477
Constructor is a special method called 'New()' in vb.net and is defined as a Sub. Overloading feature is used most frequently to overload the constructor. We overload the constructor by defining more than one 'Sub New()' procedure.
A class can have multiple constructors that assign the fields in different ways. Sometimes it's beneficial to specify every aspect of an object's data by assigning parameters to the fields, but other times it might be appropriate to define only one or a few.
In visual basic, a class can contain more than one constructor with a different type of arguments and the constructors will never return anything, so we don't need to use any return type, not even void while defining the constructor method in the class.
In VB.NET, when we pass one or more arguments to a constructor, the constructor is known as a parameterized constructor. And the object of the class should be initialized with arguments when it is created. Let's create a program to use the parameterized constructor to pass the argument in a class.
The issue is that once you specify a parametric constructor, the parameterless constructor becomes private unless explicitly specified otherwise by you.
So, modifying ken2K's code:
Namespace Presenters
Public Class BaseFooPresenter
' SPECIFYING the protected default parameterless constructor
' can also be public
Protected Sub New()
End Sub
Public Sub New(ByVal strvar As String)
' TODO with strvar variabile
End Sub
End Class
Public Class FooPresenter
Inherits BaseFooPresenter
Public Sub New(ByVal boolvar As Boolean)
MyBase.New()
' TODO with boolvar variabile
End Sub
Public Sub New(ByVal boolvar As Boolean, _
ByVal objvar As Object)
Me.New(boolvar)
' TODO with objvar variabile
End Sub
End Class
End Namespace
Just like with C#, you can't call this() and base() at the same time.
Here's what you should do:
Namespace Presenters
Public Class BaseFooPresenter
' assuming the public default parameterless constructor
Public Sub New(ByVal strvar As String)
' TODO with strvar variabile
End Sub
End Class
Public Class FooPresenter
Inherits BaseFooPresenter
Public Sub New(ByVal boolvar As Boolean)
MyBase.New(String.Empty)
' TODO with boolvar variabile
End Sub
Public Sub New(ByVal boolvar As Boolean, _
ByVal objvar As Object)
Me.New(boolvar)
' TODO with objvar variabile
End Sub
End Class
End Namespace
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