Difference between VB.Net and C# "As New WebControl"

Question

I was refactoring some code, and part of it included moving it from VB.Net to C#.

The old code declared a member like this:

Protected viewMode As New WebControl

The new code, I eventually got working, like this:

protected WebControl _viewMode = new WebControl(HtmlTextWriterTag.Span);

I can presume that the New keyword meant: call the constructor! But how was VB.Net calling a constructor (a parameter-less one) that I couldn't call in C#?

Answer 1

The reason this worked in VB, and not in C#, had nothing to do with assemblies.

The default constructor for WebControl is protected.

VB and C# have different interpretations of what "protected" means.

In VB, you can access a protected member of a class from any method in any type that derives from the class.

That is, VB allows this code to compile:

class Base
    protected m_x as integer
end class

class Derived1
    inherits Base
    public sub Foo(other as Base)
        other.m_x = 2
    end sub
end class

class Derived2
    inherits Base
end class

Because a "Derived1" is a base, it can access protected members of "other", which is also a base.

C# takes a different point of view. It doesn't allow the "sideways" access that VB does. It says that access to protected members can be made via "this" or any object of the same type as the class that contains the method.

Because "Foo" here is defined in "Derived1", C# will only allows "Foo" to access "Base" members from a "Derived1" instance. It's possible for "other" to be something that is not a "Derived1" (it could, for example, be a "Derived2"), and so it does not allow access to "m_x".

In this case of your code, VB allowed "sideways" access to the "WebControl" constructor.

C#, however, did not.

Answer 2

The default constructor for WebControl (implicit in the VB line) is to use a span. You can call that constructor in c# as well as VB.NET.