Why does my Prog work if I have pointless MsgBox and not if I don't...

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Hi All,
I have a problem caused I think by the Serial Comms thread and UI thread being out. I am reading back a value, if I put in a MsgBox it works if I have a timer Enabled to check the contents of the incoming text box (its a Rich one!)

VB

Private Sub TmrNoDataAtPort_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TmrNoDataAtPort.Tick


       While (rtbIncoming.Text = "")

       End While
       TmrNoDataAtPort.Enabled = False
       'Thread.Sleep(200)

   End Sub

That does not work however if I put into the timer

VB

txtReadFreqA.Text = rtbIncoming.Text

The numbers appear where they should be however that puts the burden on the tool box timer which I have been caught out by in the past (it works fine now but when the load of the certain PC(s) that this is for. I think I need a more certain way of doing it before I get too far with this...
Glenn

Posted 12-Feb-14 5:04am

glennPattonWork3

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TnTinMn 12-Feb-14 13:24pm

Just throwing this out there as a possible SerialPort example source.
http://www.hardandsoftware.net/Downloads.htm

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-02-12T05:38:00

It's a bad idea to use timers for communication. You could use stream much more reliably and easier. It even less understandable that you are already using a thread. You did not explain what kind of timer do you use and why.

You cannot call anything related to UI from non-UI thread. Instead, you need to use the method Invoke or BeginInvoke of System.Windows.Threading.Dispatcher (for both Forms or WPF) or System.Windows.Forms.Control (Forms only). The same goes for the timer handler (don't use the timer), unless this is the timer System.Windows.Forms.Timer. But this type of timer is too bad for most purposes except some we don't need to discuss here. Don't use any timers at all, anyway.

You will find detailed explanation of how it works and code samples in my past answers:
Control.Invoke() vs. Control.BeginInvoke()[^],
Problem with Treeview Scanner And MD5[^].

See also more references on threading:
How to get a keydown event to operate on a different thread in vb.net[^],
Control events not firing after enable disable + multithreading[^].

—SA