Object Reference and Casting

[krijgerd]

Hi everyone I'm starting on VB.net and have encounter some problems:

1._ I have two Forms (Form1 and Form2), on Form1 I have a public variable; Form1 calls Form2. My problem is that I need to change that public variable from Form2. I have (in Form2) a variable declared as Form1, but I don't know how to make that variable point to the existing instance of Form1.

2._ Is there a legal way to cast from an object to a button. 'Cause I have something like this:

Dim btn as button;
btn=sender '(which is an object);

When I use strict off I can do it fine but I get an error if I turn strict on.

Thanks for the help.

[dynamic_sysop]

Dim btn as button = DirectCast(Sender , Button)

[Pirate]

For the variable part why don't you put it in a module ?

[krijgerd]

I guess I'm going to declare it in a module, but just for knowing do you know how to do it, 'cause there's got to be a way...

[Pirate]

By passing it in the constructor I think .

[MikeStammer]

1. Do not use a module. That sure sounds like the old (wrong) way of just making everything global. That is bad programming. Here is how you do it the right way, via a reference to Form1.

Declare a variable, call it FormOne in form2 at the class level.

Private FormOne as Form1

In form2s constructor (the New method, expand the generated code section to see it), you need to add something like this

public sub New(frm1 as form1)
' put this at bottom of method
FormOne = frm1

In Form1 you create a Form2 like this:

Dim frm2 as new Form2(Me)
Frm2.show

Now you have a reference to your Form1 object that instantiated Form2, so you can reference controls like this:

FormOne.someControl.someProperty = someValue
or
FormOne.someVariable = someValue

2. If you are talking about the sender object in events, just say something like this, assuming the sender is a button of course

dim btn as button = sender

now you can call all methods and use properties of a button via your btn object. I believe VB will cast it for you using that syntax, but the other way works just as well

[nemaroller]

1) Make a public property in Form1 that changes the variable.

Then in form2, you can simply change that property by coding:

Form1.someProperty = someValue

[Pirate]

Originally posted by MikeStammer
1. Do not use a module. That sure sounds like the old (wrong) way of just making everything global. That is bad programming.

heheh . .

[MikeStammer]

Originally posted by nemaroller
1) Make a public property in Form1 that changes the variable.

Then in form2, you can simply change that property by coding:

Form1.someProperty = someValue

This will not work, ever, without a reference to form1. .NET is not VB6. In VB6 this is how it was done, but not any more.