Question

In C++, it is possible to do:

int x;
int& foo = x;

// foo is now a reference to x so this sets x to 56
foo = 56;

But is an equivalent possible in Visual Basic .net (VB.net)?

I am aware of the ByRef term in VB.net but I have only seen (and by extensive research) this in passing parameters by reference to functions/subroutines, so that the function modifies the same variable declared by the calling code.

But I haven’t seen ByRef used to declare variables (as class members or local variables). I have tried to use ByRef to do such a declaration but I get compiler errors for each ordering of the declaration I try.

The reason why I want to do this is because I want a class instance to be able to refer to a variable declared in another class instance.

Specifically, I am working on some existing VB.net code where program logic is mixed up with UI logic in VB.net form classes. I want to separate the program logic out of the form code so that it can be more easily reused. To do this I need the program logic code to be able to ‘talk’ to the form code so I need access to its variables.

I am using Visual Studio 2010 Express with VB.net and would prefer to remain within this environment even though I am aware that full Visual Studio has extended capabilities.

Answer 1

Pointers exist but they’re called object references

(Now other posters, please don’t quibble with me about the actual differences here. I am talking about the high level task the OP wants to accomplish)

Obviously you can’t do literally what you’ve said – that is, surgically manipulate one member. But if you have control of the code, you can do almost as well. And from what you describe is your problem, this method will be much better, as you can pass references to an object that has many members you wish to update, instead of having to pass many individual pointers.

First define a class:

Class MyScreenValues
    ' Properties will work... using public fields for brevity
    Public TextBox1Value as String
    Public SpinControl1Value as Integer
    public CheckBox1Value as Boolean
End Class

Now the equivalent of the code you posted:

Dim x as new MyScreenValues    'int x; 
dim foo as MyScreenValues = x  'int& foo = x;  
'// c++:  foo is now a reference to x so this sets x to 56 
'// .net: foo is now a reference to x so this sets x.SpinControl1Value to 56 
foo.SpinControl1Value = 56; 

If what you’re doing is trying to pass pointers to, say, every control on your form’s value to a sub, like so:

Button1_Click(...
    Dim MyObject as new BusinessObject
    MyObject.DoSubmit(TextBox1.Text, SpinButton1.Value, CheckBox1.Checked)

You can use the method provided by superbDeveloper, and use the ByRef keyword on the definition of the DoSubmit Sub:

Public Sub DoSubmit(ByRef Name as String, ByRef Age as Integer, ByRef Employed as boolean)
    ... business logic...

However this just gives you a 2-layer separation. Look into MVP, MVC, etc – however consider submitting the entire view worth of data. It’s a lot of research you you may settle with what you have now. For example your business logic will be firing events on the form as it changes the form values (well, actually, they won’t fire until the sub exits, due to the way VB deals with byref properties [=temp variable], but it needs to be considered).

You can also map an object’s properties to a Form’s properties with other libraries. Check out VALUE INJECTOR on the web. It can take a webform/winform and maybe even a WPF form and map the control values to and from an object you have predefined. Excellent for complete separation.