Class-Class reference-ing

[medicenpringles]

I have an application with a running total featured on all of the forms. when certain controls are interacted with on any of the forms, i need the total to be updated. this i can do. but showing the user that the total has been changed is the problem. he's the code i'm having trouble with:

' This is in frmSecond
Sub Button1_Click(parameters, blah blah..)
   
   Dim f as New frmSecond
   Dim m as New frmMain
   
   Globals.number += 1
   f.lblTotal = Globals.number.ToString
   m.lblTotal = Globals.number.ToString  ' This does not happen

End Sub

 

[ThatRickGuy]

f and m are pointing to NEW variables. What you need is to either pass a reference to the other form objects from one form to another, or to store those references globally.

-Rick

VB.Net Forum forum796 forum855 ASP.NET Forum
I believe in killer coding ninja monkeys.

 

[medicenpringles]

well see that's the problem. when i try to do just "dim m as frmMain", it gives an 'Unhandled exception of type System.NullReference exception'

is there a way of referencing the current instance of a class?

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[SBendBuckeye]

Could you put your Global update in the individual form's Activate event? Good Luck!

Have a great day!

j2consulting@yahoo.com

 

[medicenpringles]

well not the current instance... both forms are visible on the screen, but the second one is showed modally. is this a problem?

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[chrissie1]

nope you just need to pass the instance or declare the forms somewhere in a module or shared in a class

Christiaan Baes
Belgium

I just like this --> [Wiggle] [Wiggle]

 

[medicenpringles]

oh and the activate thing doesn't work.

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[medicenpringles]

so your saying i need to do something like:

Public fMain as frmMain

in my Globals module?

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[chrissie1]

yes

Christiaan Baes
Belgium

I just like this --> [Wiggle] [Wiggle]

 

[medicenpringles]

he's my code exactly:

Public Class frmMain
    Inherits System.Windows.Forms.Form
'Windows Form Designer Generated Code

    Private Sub btnTC01_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) _
    Handles btnTC01.Click
        OrderActions.Main("string")
    End Sub
End Class

which calls:

Module OrderActions
    Sub Main(ByVal Selection As String)

        Dim f As New frmCompleteOrder

        Select Case Selection
            Case "strng"
                MainForm.lstOrders.Items.Add(Prices.rgnmTC01 & _
                "   " & Prices.prcTC01_sm.ToString)
                Globals.OrderTotal += Prices.prcTC01_sm
                MainForm.lblOrderTotal.Text = Format(Globals.OrderTotal, "$0.00").ToString
                With f
                    .rdoFlatBread.Enabled = False
                    .lblOrderTotal.Text = Format(Globals.OrderTotal, "$0.00")
                End With
'there are more cases here
        End Select
End Sub

he's the Prices class:

Public Const rgnmTC01 as String = "yeah"
Public Const prcTC01 as Double = 3.29

And here's the globals

Public Module Globals
    Public OrderTotal As Double
    Public MainForm As New frmMain
End Module

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[medicenpringles]

one correction:

Module OrderActions
    Sub Main(ByVal Selection As String)

        Dim f As New frmCompleteOrder

        Select Case Selection
            Case "strng"
                MainForm.lstOrders.Items.Add(Prices.rgnmTC01 & _
                "   " & Prices.prcTC01_sm.ToString)
                Globals.OrderTotal += Prices.prcTC01_sm
                MainForm.lblOrderTotal.Text = Format(Globals.OrderTotal, "$0.00").ToString
                With f
                    .rdoFlatBread.Enabled = False
                    .lblOrderTotal.Text = Format(Globals.OrderTotal, "$0.00")
                End With
	[b]f.ShowDialog()[/b]
End Sub

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[ThatRickGuy]

Step 1: Read This FAQ: faq796-5611

Then look at it from the house analogy:

When you define the class frmMain, it is like making blueprints.

When you instantiate an object of type frmMain with the New keyword, it creates that object in memory. This is like building the house at 123 Anystreet.

When you try to reference that object from another class, you need to reference that memory location. Or in the case of the house, you are looking for the house at 123 Anystreet.

If you create another NEW object of the same type, it will be at a different memory location. This would be like mailing a letter to 125 Anystreet which just happens to be the same TYPE of house, but not THE same house.

-Rick


VB.Net Forum forum796 forum855 ASP.NET Forum
I believe in killer coding ninja monkeys.

 

[medicenpringles]

well i understand that, but again, if i set the variable to "Dim MainForm as frmMain, it gives me a null reference exception. is there a way to reference a particular instance? or, what do i need to set my variable as?

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[ThatRickGuy]

You need to have a reference to the Object you want to access. That means you need to either store those variables globally, or pass the variables to each method that needs to access them.

You can also pass those variables to a constructor, and then set local variables equal to them. See this FAQ: faq796-5773 for more information on passing objects from one form to another.

-Rick

VB.Net Forum forum796 forum855 ASP.NET Forum
I believe in killer coding ninja monkeys.

 

[chiph]

Global variables.
Shudder.

Chip H.


____________________________________________________________________
If you want to get the best response to a question, please read FAQ222-2244 first

 

[chrissie1]

Modules.
Double Shudder.

Christiaan Baes
Belgium

I just like this --> [Wiggle] [Wiggle]

 

[earthandfire]

chrissie:

nope you just need to pass the instance or declare the forms somewhere in a module

and


Modules.
Double Shudder


I'm confused.


chip:

Global variables.
Shudder


What do you suggest instead of Global variables - or are you implying Public variables in a Module = bad and Public Shared members (variables) in a Public Class = good (or at least ok)?

 

[chrissie1]

I aim to please.

And I deny ever saying this "nope you just need to pass the instance or declare the forms somewhere in a module
"

Christiaan Baes
Belgium

I just like this --> [Wiggle] [Wiggle]

 

[ThatRickGuy]

Public shared members != global variables.

-Rick

VB.Net Forum forum796 forum855 ASP.NET Forum
I believe in killer coding ninja monkeys.

 

[chrissie1]

Public shared members != global variables.

details, details.


Christiaan Baes
Belgium

I just like this --> [Wiggle] [Wiggle]