BackgroundWorker and shared class - vb.net

Question

I have a NumericUpDown control in the main thread.
I create an instance of a public class_A that stores the NumericUpDown value.
I create a BackgroundWorker that runs a separate thread.
In the BackgroundWorker thread I create an instance of a class_B that recalls the argument from the instance of class_A.
I don't understand why the instance of the class_A just created before, its result as Nothing.
Here is the code:
Imports System.ComponentModel
Public Class Form1
Dim WithEvents bgw As New BackgroundWorker
Dim WithEvents bgw2 As New BackgroundWorker
Dim lSide As Label
Public nudSide As NumericUpDown
Dim bCalculate As Button
Dim bCalculate2 As Button
Dim tbLog As TextBox
Dim calc As calc
Public calc2 As calc2
Public Delegate Function d_getSide() As Double
Public getSide As New d_getSide(AddressOf rungetSide)
Public Side As c_Side
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.Size = New Size(400, 160)
bgw.WorkerSupportsCancellation = True
bgw2.WorkerSupportsCancellation = True
lSide = New Label
With lSide
.Text = "Side"
.Size = New Size(40, 20)
.Location = New Point(10, 10)
End With
Me.Controls.Add(lSide)
nudSide = New NumericUpDown
With nudSide
.Size = New Size(40, 20)
.Location = New Point(lSide.Location.X + lSide.Size.Width, lSide.Location.Y)
.DecimalPlaces = 0
.Minimum = 1
.Maximum = 100
.Increment = 1
.Value = 1
End With
Me.Controls.Add(nudSide)
bCalculate = New Button
With bCalculate
.Text = "Calculate"
.Size = New Size(60, 20)
.Location = New Point(nudSide.Location.X + nudSide.Size.Width + 40, nudSide.Location.Y)
AddHandler .Click, AddressOf bCalculate_Click
End With
Me.Controls.Add(bCalculate)
bCalculate2 = New Button
With bCalculate2
.Text = "Calculate 2"
.Size = New Size(60, 20)
.Location = New Point(bCalculate.Location.X + bCalculate.Size.Width + 10, bCalculate.Location.Y)
AddHandler .Click, AddressOf bCalculate2_Click
End With
Me.Controls.Add(bCalculate2)
tbLog = New TextBox
With tbLog
.Size = New Size(250, 60)
.Location = New Point(lSide.Location.X, lSide.Location.Y + 40)
.Multiline = True
.ScrollBars = ScrollBars.Vertical
End With
Me.Controls.Add(tbLog)
End Sub
Private Sub bCalculate_Click()
bgw.RunWorkerAsync(nudSide.Value)
End Sub
Private Sub bgw_Dowork(sender As Object, e As DoWorkEventArgs) Handles bgw.DoWork
'example 1)
'passing argument throught backGroundWorker
calc = New calc(e.Argument)
End Sub
Private Sub bgw_Runworkercompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles bgw.RunWorkerCompleted
getResult()
End Sub
Private Sub bCalculate2_Click()
'here i create an instance of the Side class (expose the side property)
Side = New c_Side
bgw2.RunWorkerAsync()
End Sub
Private Sub bgw2_Dowork(sender As Object, e As DoWorkEventArgs) Handles bgw2.DoWork
'example 2)
' in the backgroundworker thread i create an instance of the class calc2
calc2 = New calc2()
End Sub
Private Sub bgw2_Runworkercompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles bgw2.RunWorkerCompleted
getResult2()
End Sub
Private Sub write(ByVal message As String)
With tbLog
.SelectionStart = .Text.Length
.SelectedText = vbCrLf & message
End With
End Sub
Private Sub getResult()
tbLog.Clear()
write("area = " & calc.area & " cm^2")
write("volume = " & calc.volume & " cm^3")
End Sub
Private Sub getResult2()
tbLog.Clear()
write("area = " & calc2.area & " cm^2")
write("volume = " & calc2.volume & " cm^3")
End Sub
Public Function rungetSide() As Double
If Me.InvokeRequired Then
Me.Invoke(getSide)
Else
Return Side.Side
End If
Return Side.Side
End Function
End Class
Class calc
Sub New(ByVal Side As Double)
_area = Side ^ 2
_volume = Side ^ 3
End Sub
Private _area As Double
Public Property area As Double
Get
Return Math.Round(_area, 2)
End Get
Set(value As Double)
_area = Math.Round(value, 2)
End Set
End Property
Private _volume As Double
Public Property volume As Double
Get
Return Math.Round(_volume, 2)
End Get
Set(value As Double)
_volume = Math.Round(value, 2)
End Set
End Property
End Class
Public Class calc2
Sub New()
'the constructor, recall the value from the instance (public) of the class 'Side' just built in the main thread
'but i don't understand why the instance it's nothing
_area = Form1.Side.Side ^ 2
_volume = Form1.Side.Side ^ 3
End Sub
Private _area As Double
Public Property area As Double
Get
Return Math.Round(_area, 2)
End Get
Set(value As Double)
_area = Math.Round(value, 2)
End Set
End Property
Private _volume As Double
Public Property volume As Double
Get
Return Math.Round(_volume, 2)
End Get
Set(value As Double)
_volume = Math.Round(value, 2)
End Set
End Property
End Class
Public Class c_Side
Sub New()
_Side = Form1.nudSide.Value
'_Side = Form1.rungetSide
End Sub
Private _Side As Double
Public Property Side As Double
Get
Return Math.Round(_Side, 2)
End Get
Set(value As Double)
_Side = Math.Round(value, 2)
End Set
End Property
End Class
What I'm looking for is to create an instance of class_A in the main thread and store the NumericUpDown value, and in a separate thread (BackgroundWorker) create an instance of class_B and obtain the value of the NumericUpDown control, just before stored in the instance of class_A.

Answer 1

I've found the solution.
Just declare the variable as Public Shared
Public Shared Side As c_Side
So it's visible from all the application, and so, from all the threads.
So when i start the thread (or when i want or when i need), i backup all the values of the UI controls in a Public Shared instance of a Public Class, that can be 'read' from the backGroundWorker thread.