Rich textbox and string differing

Glenn Patton

Hi All,

First question, I am reading a serial port and putting output to a string,
but the string is blank, however if I stick a message box in, it causes enough of a gap to allow the text to appear in the string. I am using a delay based on the length of the expected reply.
The line of code that appears is reply = rtbIncoming.text.
rtbIncoming.Text has a string in it from the device. Is it because of seperate threads the reply in the text box appears on one thread, there is not enough of a delay for it to get from the comms thread to the UI thread?

Glenn

9 Replies

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Vulpes14y ago
Accepted answer
The Invoke method is synchronous and will therefore block the thread until it completes.

You could try using BeginInvoke instead which is asynchronous and therefore returns immediately:

this.BeginInvoke(new MethodInvoker(delegate()
{
rtbIncoming.Text = reply;
}));
Vulpes14y ago
Funnily enough, I recommended the following very good threading resource to some one else today.

I've also added a good resource on delegates and events:

http://www.albahari.com/threading/

http://www.akadia.com/services/dotnet_delegates_and_events.html
Glenn Patton14y ago
Hi Vulpes,

Been in the lab for an hour or so, so didn't see your reply
in the past I have only used BeginInvoke and was a little unsure of Invoke but with the previous changes & that one the program now responds correctly.

this.BeginInvoke(new MethodInvoker(delegate()
{
rtbIncoming.Text = reply;
}));

I do really need to understand the delegate methods better & threading as a whole better could you recomend any resource?

Glenn
Glenn Patton14y ago
Hmmm,
It looks like if I only enable the button once it has finished it gets around the problem.... Need my PC to go into one it's hard drive grinding moments.....

Glenn
Glenn Patton14y ago
Hi,

Spotted a problem, if the machine is busy (mine was hammering the hard drive!) obviously the invoke method is very dependant on the use of the processor! Is there a source of info that (MircoSoft) is regaurded as official. As this I would like to check to see if there is a system legal way of making it a higher priority to always fire. This is getting away from my area of speciality into the Windows domain (beyond that point lies madness!)

Glenn
Glenn Patton14y ago
Hi Vulpes,
Same guy different forum (I can't be the only person to mess with Serial Ports though!) to give you an update some problems with the board mean that
testing can only be done on one part of the board but it 'Works!!!' thank you I just moved where I was declaring the delegate etc.

this.Invoke(new MethodInvoker(delegate()
{
rtbIncoming.Text = reply;
}));
to just after the command is sent and it works!!!! about the handler name
port_DataReceived_1 that is the only noncommented interrupt handler
it was my name not Visual Studio's (great minds think alike, ah no wait....)
to fit in with others coding style (?) roll on Friday!!
Thanks
(how do I give you reputation points here?)
Glenn
Vulpes14y ago
Hello Glenn,

As it was a question about the SerialPort, I wondered whether it might be you ;)

One thing that's worrying me about that code is the name of the handler:

port_DataReceived_1

The _1 is usually a sign that a handler has been added twice by the VS designer.

I'd check the Properties Box for the SerialPort component to see whether there are two handlers listed for the DataReceived event.

If there are, then the first handler may be grabbing the string, leaving nothing in the buffer to be read by the second handler! That might explain why nothing is getting written to the richtextbox.
Glenn Patton14y ago
Hi Vulpes, ex debugging.com, hello.

Umm tried a delegate in the event handler it didn't work and led to the issue see below:

private void port_DataReceived_1(object sender,SerialDataReceivedEventArgs e)
{

//int valueWait = WaitForData(12, 10);
InputData = myComPort.ReadExisting();
if (InputData != String.Empty)
{
this.BeginInvoke(new SetTextCallback(SetText), new object[]{ InputData});
}
}
Tried using the delegate you suggested with the same results!
I am a little condfused.
Vulpes14y ago
If you're receiving the string in the SerialPort's DataReceived eventhandler and then assigning it to a textbox, the problem may be that you're not marshalling the assignment back to the UI thread which is generally necessary when dealing with controls (it doesn't matter for MessageBox.Show).

So instead of a line like this:

rtbIncoming.Text = reply;

I'd try code like this:

this.Invoke(new MethodInvoker(delegate()
{
rtbIncoming.Text = reply;
}));

This assumes the DataReceived eventhandler is in your Form class - not a separate class.