Update Label And ProgressBar value from another class invoked in a background worker - vb.net

Question

hello I have a problem to update a progress bar and a label inside a StatusStrip in the main form.
there are 2 controls in the form inside a StatusStrip:
Progressbar (ToolStripProgressBar)
ProgressLabel (ToolStripStatusLabel)
Basically I have this situation:
Public Class Main
Public Sub TEST(ByVal sender As Object, ByVal e As DoWorkEventArgs) Handles TEST.DoWork
Dim tmp as New NAMESPACE1.CLASS2(VALUES)
End Sub
End Class
Namespace NAMESPACE1
Public Class CLASS2
Public Sub New(VALUES)
Main.Progressbar.Value = 15
Main.ProgressLabel.Text = "hello!"
End Sub
End Class
End Namespace
The problem is that text or value of the controls are updated (I see it using breakpoints) in the code but not in the form in which progressbar is always a 0% and label always as nothing.
I think it's an update or refresh problem of the main form. i have tried to do Main.Refresh() and Main.Update() but it does not work anyway.
Thanks in advance.

Answer 1

You have 2 issues in play. The first is that Main is a class name, not a runtime reference or object variable. See Idle_Mind's answer for using Me to get the runtime object reference.
The second problem is that since Class2 is created in DoWork, it is created on the background thread, which will prevent it from accessing UI controls (which are created on the UI thread). You will get an illegal cross thread operation exception (even if you dont see it).
I'd suggest that Class2 does nothing useful which can't be done using the ReportProgress method. Getting rid of it also gets rid of the form reference issue since an event is raised on the same thread as the UI controls:
Private WithEvents bgw As BackgroundWorker
...
' in a button click or whatever starts the worker:
bgw = New BackgroundWorker
bgw.WorkerReportsProgress = True
bgw.RunWorkerAsync(5) ' times to loop
...
Private Sub bgw_DoWork(sender As Object,
e As DoWorkEventArgs) Handles bgw.DoWork
' NOTE
' This code executes on a different thread
' so do not reference UI controls!
' e.Argument is the value passed - amount of work
Dim max As Integer = CInt(e.Argument)
For n As Integer = 1 To max
Threading.Thread.Sleep(250) ' emulates work
' causes the ProgressChanged event to fire:
bgw.ReportProgress(n, String.Format("{0} of {1}", n.ToString, max.ToString))
Next
End Sub
Private Sub bgw_ProgressChanged(sender As Object,
e As ProgressChangedEventArgs) Handles bgw.ProgressChanged
'ProgressChanged fires on the UI thread, so it is safe to
' referenece controls here
TextBox4.Text = e.UserState.ToString
TextBox4.Refresh()
End Sub
Paste the code and you can see the message change in the TextBox. The same would work using your ProgressBar and ProgressLabel.
bgw.ReportProgress(n, arg)
The first argument will map to e.ProgressPercentage in the ProgressChanged event. The second is optional - UserState. I used it to pass a string for illustrative purposes (the form can already know the amount of work since it told the BGW what to do.)
If Class2 has some other purpose, you can use it as long as it is created on the UI thread (in the form) and used on that thread (ie in ProgressChanged event). You also need a method to talk to the controls so you dont have to create a new one each time:
Private myObj As Class2 ' declaration
...
myObj = New Class2(Me) ' instance with frm ref
In class2:
Public Sub Update(value As Integer, msg As String)
frmMain.Progressbar.Value = value
frmMain.ProgressLabel.Text = msg
End Sub
Then in the ProgressChanged event:
myObj.Update(x, y)
Where x and y are the value and message from whereever.

Answer 2

Here's an example of passing a reference to MAIN as suggested by Plutonix. I've intentionally left your pseudo-code style intact:
Public Class MAIN
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
TEST.RunWorkerAsync()
End Sub
Private Sub TEST_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles TEST.DoWork
Dim tmp As New NAMESPACE1.CLASS2(Me, VALUES) ' <-- Form reference being passed via 1st parameter
End Sub
End Class
Namespace NAMESPACE1
Public Class CLASS2
Private frmMain As MAIN
Public Sub New(ByVal frmMain As MAIN, VALUES)
Me.frmMain = frmMain
Me.frmMain.Progressbar.Value = 15
Me.frmMain.ProgressLabel.Text = "hello!"
End Sub
End Class
End Namespace