VB.net Cross-Thread

Question

Hello,

I have a cmd command that needs to be executed, when the command starts it starts to fill a progressbar. When the cmd command is done the progressbar needs to fill up to 100.

This is the code i use, but it gives me an error when the progressbar.Value = 100 comes up.

Public Class Form1
    Dim teller As Integer

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TimerProgressbar.Tick
    teller += 1
    ProgressBar1.Value = teller

    If ProgressBar1.Value = ProgressBar1.Maximum Then
        TimerProgressbar.Stop()
    End If
End Sub

This are the tow commands in another private sub where the app is crashing on

ProgressBar1.Value = 100
    TimerProgressbar.Stop()

When i debug it and i try it out it crashes on

ProgressBar1.Value = 100

But when i build it under Windows 7 it runs fine without crashing, however a few people reported me it crashes on there Windows xp system.

VB gives me a suggestions about Cross Thread, but i don't know how i could make it work with this.

Answer 1

You can only access (with one exception) a Window's (or anything tied to Window) properties and methods from the thread that created that Window.

But WinForms includes support for this with the Invoke (and BeginInvoke) methods to perform a cross thread call, with the InvokeRequired property.

If InvokeRequired is true, then you need to use Invoke to cross threads. To do this wrap your code that manipulates the control in its own method, and either call directly, or via Invoke. (To perform the operation cross threads asynchronously use BeginInvoke instead.) Something like:

Private Sub IncrementProgress()
    teller += 1
    ProgressBar1.Value = teller

    If ProgressBar1.Value = ProgressBar1.Maximum Then
        TimerProgressbar.Stop()
    End If
End Sub      

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TimerProgressbar.Tick
  if ProgressBar1.RequiredInvoke Then
    ProgressBar1.Invoke(IncrementProgress)
  Else
    IncrementProgress
  End If
End Sub