Question

Would anyone be able to help me here please. I’m fairly new to VB.net and threading so im just trying to figure out what is happening.

When I debug this I am getting the error

thread operation not valid: Control ‘ProgressBar1’ accessed from a
thread other than the thread it was created on.

I’m a little lost as to why the error is occuring or how to fix it. I’ve had to put the progress bar in a separate thread otherwise the GUI crashes

Private Sub InstallTheAgent_Click(ByVal sender As System.Object, ByVal e As     System.EventArgs) Handles InstallTheAgent.Click
    MsgBox("Click OK to continue to install the Agent")
    Dim t As Thread

    t = New Threading.Thread(AddressOf WorkInstallAgent)
    t.Start()
End Sub

Private Sub WorkInstallAgent()
    ProgressBarThread()
    Dim DeviceLines As String() = IO.File.ReadAllLines(DynPath & "\machines.txt")
    ProgressBar1.Minimum = 0
    ProgressBar1.Maximum = DeviceLines.Length

    Using myReader As System.IO.StreamReader = My.Computer.FileSystem.OpenTextFileReader(DynPath & "\machines.txt")
        ProgressBarThread()
        Do While myReader.Peek() >= 0

            Dim computerName As String = myReader.ReadLine
            If My.Computer.Network.Ping(computerName) = True Then
                Call CopyAgent(computerName)
                Call InstallAgent(computerName)
                Call Agent(computerName)
                Call RemoveTempSoftware(computerName)
            End If
            ProgressBar1.Value = ProgressBar1.Value + 1
        Loop
    End Using

    MsgBox("Installation of the Agent Complete")
    ProgressBar1.Value = 0


End Sub

Public Sub ProgressBar()

    If Me.InvokeRequired Then
        Me.Invoke(New MethodInvoker(AddressOf ProgressBar))
    Else
        Dim DeviceLines As String() = IO.File.ReadAllLines(DynPath & "\machines.txt")
        ProgressBar1.Minimum = 0

        ProgressBar1.Maximum = DeviceLines.Length
    End If
End Sub

Public Sub ProgressBarThread()
    Dim p As Thread

    p = New Threading.Thread(AddressOf ProgressBar)
    p.Start()

End Sub

Answer 1

Progress bar is on GUI thread. If you try to access it form other thread then this error will occur.

Try usin Background worker. Check this link:
http://www.java2s.com/Code/VB/GUI/BackgroundWorkerDemo.htm