Cross Thread Problem with SerialPort DataReceived Event

I am writing a custom Ref Class with C++ 2005 to control a measurement instrument via Serial Port.

My class inherets System::IO::Ports::SerialPort.

I also define events inside my class to generate action on specific RS232 messaages.

My problem is as follows: Inside the datareceived event handler, I raise events based on messages reveived. However, when my class is instantiated on a windows form, if the event handler defined on the form changes properties of a textbox control, the sytem generates "System.InvalidOperation Exception" and goes on to describe that a different thread tried to access the control.

I can solve the problem by setting the CheckForIllegalCrossThreadCalls property of the Windows Form to false. I do not like this solution, because it seems unsafe, and if someone other than myself was using my class, it might produce unexpected results in their program.

I can also solve the problem using the invoke method of the form / control with delegates to produce a thread safe call as described here:

The fix on this is relatively simple I believe

first set up a delegate

// the text property on a TextBox control.

delegate void SetTextCallback(string text);

inside your DataRecieved event put this code

string textIn = serialPort1.ReadExisting();

Then build a method called SetText as follows

private void SetText(string text)

// InvokeRequired required compares the thread ID of the

// calling thread to the thread ID of the creating thread.

// If these threads are different, it returns true.

if (this.txtDataIn.InvokeRequired)

SetTextCallback d = new SetTextCallback(SetText);

this.Invoke(d, new object[] { text });

else

this.txtDataIn.Text = this.txtDataIn.Text + text;

This code sends the data from the serial port to a textbox but you can sub whatever control that you want to recieve the data

Hope this helps,

PatC

This looks like what I need. I am not that good with C#, but I am farmiliar enough that I think I can make it work. If you have time Id still like to see it properly in C++, since I am only just starting to use delegates / events.

I do have a question though -

private SynchronizationContext synchronizationContext = WindowsFormsSynchronizationContext.Current;

I get the point of this, as it syncs to the current form thread... What will happen here if someone used my class in a console app Should I be somehow checking the current context to make sure there is a form, and if not, raising the event differently

Great Post -

Thanks

Mikey0727 wrote:

This looks like what I need. I am not that good with C#, but I am farmiliar enough that I think I can make it work. If you have time Id still like to see it properly in C++, since I am only just starting to use delegates / events. I do have a question though - private SynchronizationContext synchronizationContext = WindowsFormsSynchronizationContext.Current; I get the point of this, as it syncs to the current form thread... What will happen here if someone used my class in a console app Should I be somehow checking the current context to make sure there is a form, and if not, raising the event differently

private: // data
SynchronizationContext^ synchronizationContext;

public: // c'tor
MyClass()
{
this->synchronizationContext = SynchronizationContext::Current;
}

protected: // instance methods
void OnMyEvent(EventArgs^ e)
{
if ((this->MyEvent != nullptr))
{
if ((this->synchronizationContext != nullptr))
{
this->synchronizationContext->Send((IDelegateCreateExpression NYI), e);
}
else
{
this->MyEvent->Invoke(this, e);
}
}
}
private: // implementation
void OnMyEventInternal(Object^ state)
{
this->MyEvent->Invoke(this, dynamic_cast<EventArgs^>(state));
}

public: // instance methods
void SomethingToCauseEvent()
{
this->OnMyEvent(EventArgs::Empty);
}
};

Hi

I am sorry, I am having trouble with this:

this->synchronizationContext->Send((IDelegateCreateExpression NYI), e);

as the argument for send, I had:

this->synchronizationContext->Send(gcnew System::Threading::SendOrPostCallback(&MyClass::OnMyEventInternal), e);

That didnt work, can you elaborate on: Send((IDelegateCreateExpression NYI)

thanks -

Thanks -

Last Question (I promise LOL) - in the C# example, to set the context, you use