Multiple Forms

[xyz777]

iv'e got two forms, the first is Mainform and second_form

wha i am trying to do, is to access a button on the mainform from the second form,,,,,,,

while running the second form, i managed to do

Dim mf as new mainform

mf.button1.text = " new text updated"

but i found out that i have now two mainform opened,,,,,

and i couldnt' manage to change the data from mainform1

so what u advise me to do in this situation,



thank for helping

[MrPolite]

Originally posted by xyz777
iv'e got two forms, the first is Mainform and second_form

wha i am trying to do, is to access a button on the mainform from the second form,,,,,,,

while running the second form, i managed to do

Dim mf as new mainform

mf.button1.text = " new text updated"

but i found out that i have now two mainform opened,,,,,

and i couldnt' manage to change the data from mainform1

so what u advise me to do in this situation,



thank for helping

you have to understand how classes work. A form is a class. You need to have a reference to the form to be able to access it.
If you want to be able to access a form from another form, you can pass a reference to the form in the new constructor (have to change the constructor yourself), or you could just declare the forms publicly in a module. Something like this:

Module Module1
    ' Change Form1 to whatever you want
    Public frm1, frm2 As Form1
 
    Sub Main()
        frm1 = New Form1        
        frm2 = New Form1
 
        ' runs your app with frm1
        Application.Run(frm1)
    End Sub
End Module

you can access frm1 and frm2 anywhere in your app if you put that code in a module

edit: umm make sure you change the startup object to the module. If you dont know how: right click on your project in the Solution Explorer, click on Properties. In the left hand make sure Common Properties/General is selected. in the left section choose Sub Main from the "Startup object" dropdown

[taxes]

Hi xyz777,

I read your question differently from Mr Polite. As I read it you are wondering why you have two different MainForms opened.

I suspect that you have used MainForm as the application start form, or at least have created an instance of it in a Sub Main procedure. Therefore, when you placed the code
"Dim mf as new mainform"
in the second form, you created a second and entirely separate instance of MainForm, causing confusion (to you not VB.NET).

Remove the above code and alter the call to

MainForm.button1.text = " new text updated" (assuming that MainForm is the name you hav declared)

This works provided that MainForm is still open.

For More involved aspects see:


http://www.vbforums.com/showthread.p...hreadid=276165

and for an unusual alternative:

http://www.vbforums.com/showthread.p...hreadid=276604

[shadowfyre]

Sorry to drag this up out of the tar pits of time, but I'm haing a very similar problem that the suggested solution does not work for.

My particular line of code is:

Form1.TabControl1.SelectedIndex = Me.ListBox1.SelectedIndex

That is called from Form2 (me = Form2). I get the build error:

Reference to a non-shared member requires an object reference

And "Form1.TabControl1" is underlined in my code.

Form1 is where the application starts from and it calls Form2. Both instances are open and shown. Form2 is trying to set a value on Form1. What am I doing wrong?

[salvelinus]

Form2 doesn't know anything about Form1. It's sort of like trying to use integer variable x in sub A when it's declared in sub B.
The easiest solution would be to declare the forms in the module, as above.

[shadowfyre]

I tried that:

Module Module1
    Public PaddbFlag, lbflag As Integer
    Public Frm1 As Form1
    Public Frm2 As New Form2
 
    Public Sub Main()
        Frm1 = New Form1
        Application.Run(Frm1)
    End Sub
End Module

I get this error when I try to execute the code on form2:

An unhandled exception of type 'System.NullReferenceException' occurred in Test006.exe

Additional information: Object reference not set to an instance of an object.

How can I be sure that the program is starting in Sub Main and not in Form 1?

[salvelinus]

When you reference Form1 from Form2, don't call it Form1, call it Frm1, in your example. That's the name you gave it. Otherwise it's like saying

dim i as integer
For integer = 0 to yadayada...

[taxes]

Hi,

Just to clarify what salvelinus siad;

When you create an instance of a form, that form exists ONLY under the name you gave it in the instancing.

e.g.
Where fcls1 and fcls2 are the forms, or more correctly the Form SubClasses, you created in the designer

In Module
Public frm1 as new fcls1
Public frm2 as new fcls2


In a sub or method in frm1 you refer to any object in frm2 as, e.g.
frm2.TextBox1

fcls1 and fcls2, your originally designed forms (subclasses) do not exist in your runtime application - one of the big differences from VB6.


Hope this helps.

[Dooglo]

Thanks everyone for replying.


BUT I found someone who explained it very understandably.


http://www.devcity.net/net/article.a...=multipleforms

This link has a zip file with full sample code.

Thanks,

[shadowfyre]

Well, thanks to Dooglo's article, I was able to get it to work by overloading Form2's constructor method and by passing Form1 as an arguement, i.e. Dim frm2 As New Form2(Me). By passing the arguement to Form2's constructor, I was able to assign it to a variable. This gives Form2 a direct link to Form1. Worked like a charm.

But I'm still a bit hazy on this instanciation stuff. Here's where you guru's get to educate a relative noob.

Is there a way to assign a varible to an already existing instance of an object? Maybe I'm not using the right words. In the statement, "Dim frm2 As New Form2," not only are you creating a new instance of Form2, but you are also assigning a variable, frm2, to it, right? Or do I have this wrong?

Is "Dim frm2 As Form2" - notice the abscense of "New"- a valid statement? I guess that it would be. It creates the varible, frm2, but does not assign it to any particular instance of a Form2. Is there a way of assigning frm2 to an already existing instance of Form2?