Accessing a form from a thread running on a second form

[Wagz]

Hi,

I have a main form which starts up a thread as well as a 2nd form.

How do I make it so that I can access things such as labels on the 2nd form from the thread that was started on form1?

I have some sample code below...

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Form2.Show()
        Form2.BringToFront()
        signal = New Class1
    End Sub
    Private signal As Class1

End Class


Public Class Class1
    Public Sub New()
        trd = New Threading.Thread(AddressOf task)
        trd.IsBackground = True
        trd.Start()
    End Sub
    Private trd As Threading.Thread
    Private Sub task()
        For i As Integer = 0 To 5
            Threading.Thread.Sleep(5000)
            Form2.Label1.Text = i.ToString
        Next
    End Sub
End Class

Any help would be much appreciated.

Thanks,

Wagz

[Shashi Sadasivan]

have you tried passing the instance of Form1 to both Form2 and signal ?

[Wagz]

It appears that every time I'm in the created thread and call something from form2 that it creates a new instance of the form. How do I reference the form that form1 created from the created thread?

[jjvainav]

The best approach to this would be to create an event in Class1 that gets raised whenever you want to indicate progress from your thread.

        For i As Integer = 0 To 5
            Threading.Thread.Sleep(5000)
            ' Form2.Label1.Text = i.ToString
            ' singal event here
        Next

Then from your Form1 class you can handle the event and then set your label for form2

Private Sub SomeEventHandler
   ' If Me.InvokeRequired
   ' Me.Invoke(new EventHandler(SomeEventHandler))
   ' End If
   '
   ' Set label for Form2
End Sub

Note that you need to invoke back to the main thread in order to set the label for Form2.

I hope this helps, it is pseudo code but should hopefully explain what you need to do.

Hi,

I have a main form which starts up a thread as well as a 2nd form.

How do I make it so that I can access things such as labels on the 2nd form from the thread that was started on form1?

I have some sample code below...

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Form2.Show()
        Form2.BringToFront()
        signal = New Class1
    End Sub
    Private signal As Class1

End Class


Public Class Class1
    Public Sub New()
        trd = New Threading.Thread(AddressOf task)
        trd.IsBackground = True
        trd.Start()
    End Sub
    Private trd As Threading.Thread
    Private Sub task()
        For i As Integer = 0 To 5
            Threading.Thread.Sleep(5000)
            Form2.Label1.Text = i.ToString
        Next
    End Sub
End Class

Any help would be much appreciated.

Thanks,

Wagz

[Wagz]

If I pass Form2 to Class1 when I create it and create a delegate to handle the changing the text then it works.

I passed it in to Class1 in the constructor, is there a better way to do this? In the future I'd like to be able to possibly add additional forms and therefore don't necessarily want to have to have to modify the class every time I create a new form.

Below is the code I used:

Public Class Class1
    Public Sub New(ByVal Form2)
        trd = New Threading.Thread(AddressOf task)
        trd.IsBackground = True
        trd.Start()
        Me.Form2 = Form2
    End Sub
    Private Form2 As Form2
    Private trd As Threading.Thread
    Delegate Sub SetText(ByVal label As Windows.Forms.Label, ByVal text As String)
    Private Sub task()
        For i As Integer = 0 To 5
            Threading.Thread.Sleep(5000)
            Dim DelSetText As SetText = New SetText(AddressOf Form2.SetText)
            Form2.Invoke(DelSetText, New Object(1) {Form2.Label1, i.ToString})
        Next
    End Sub
End Class

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Form2.Show()
        Form2.BringToFront()
        signal = New Class1(Form2)
    End Sub
    Private signal As Class1

End Class

Public Class Form2
    Public Sub SetText(ByVal label As Windows.Forms.Label, ByVal item As String)
        label.Text = item
    End Sub
End Class

[Wagz]

jjvainav, I couldn't get your method to work.

I raised the event in Class1 and handled it in Form1, but when I go to change the text in Form2 it creates a new instance of Form2.

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Form2.Show()
        Form2.BringToFront()
        signal = New Class1()
    End Sub
    Private WithEvents signal As Class1
    Public Sub SetForm2Text(ByVal text As String) Handles signal.SetText
        Form2.Label1.Text = text
    End Sub
End Class

Public Class Class1
    Public Sub New()
        trd = New Threading.Thread(AddressOf task)
        trd.IsBackground = True
        trd.Start()
    End Sub
    Public Event SetText(ByVal text As String)
    Private trd As Threading.Thread
    Private Sub task()
        For i As Integer = 0 To 5
            Threading.Thread.Sleep(5000)
            RaiseEvent SetText(i.ToString)
        Next
    End Sub
End Class

[jjvainav]

Try this:

Public Class Form1
    Private Delegate Sub SetTextCallback(ByVal text As String)

    Private form2 As Form2

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        form2 = New Form2
        form2.Show()
        form2.BringToFront()
        signal = New Class1()
    End Sub
    Private WithEvents signal As Class1
    Public Sub SetForm2Text(ByVal text As String) Handles signal.SetText
        If Me.InvokeRequired Then
            Me.Invoke(New SetTextCallback(AddressOf SetForm2Text), text)
        End If

        form2.Label1.Text = text
    End Sub
End Class

Public Class Class1
    Public Sub New()
        trd = New Threading.Thread(AddressOf task)
        trd.IsBackground = True
        trd.Start()
    End Sub
    Public Event SetText(ByVal text As String)
    Private trd As Threading.Thread
    Private Sub task()
        For i As Integer = 0 To 5
            Threading.Thread.Sleep(1000)
            RaiseEvent SetText(i.ToString)
        Next
    End Sub
End Class

jjvainav, I couldn't get your method to work.

I raised the event in Class1 and handled it in Form1, but when I go to change the text in Form2 it creates a new instance of Form2.

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Form2.Show()
        Form2.BringToFront()
        signal = New Class1()
    End Sub
    Private WithEvents signal As Class1
    Public Sub SetForm2Text(ByVal text As String) Handles signal.SetText
        Form2.Label1.Text = text
    End Sub
End Class

Public Class Class1
    Public Sub New()
        trd = New Threading.Thread(AddressOf task)
        trd.IsBackground = True
        trd.Start()
    End Sub
    Public Event SetText(ByVal text As String)
    Private trd As Threading.Thread
    Private Sub task()
        For i As Integer = 0 To 5
            Threading.Thread.Sleep(5000)
            RaiseEvent SetText(i.ToString)
        Next
    End Sub
End Class

[Shashi Sadasivan]

All forms that you create inheri the base class Form.

If you can identify which forms will be sent (like you send Form1) to Class1
Also identify the methods that these forms will have in common,

Put them all into an interface, and pass the instance of the Form as the interface type you just created.

This way, you will only need to pull the interface type, and call the method, which will do the trick for you