First attempt to display serial port data on GUI

[marcel]

No, you just pass the same string, reinitialized. You don't delete it, just empty it. You will delete it just once, in the destructor of the worker thread.

You only have to be careful that you don't use the pointer to the QString after you delete the worker thread.

Regards

[ShaChris23]

Here's my "final" implementation. It uses a thread to read data from the serial port, and sends a signal to a GUI class to slot update the value to the screen. The CPU load on this is 0-1% as the Serial Port Read is a true blocking function call.


There are 2 remarks about this:

1) I notice that as time goes on, the program's memory keeps increasing (I checked from Windows task manager. Not a lot, about 4 KB per minute. I couldnt think of anything that could cause this. I tried taking out the serial port Read code, and the program's size still kept increasing. Can it be because of signal/slot?

2) I'm currently passing signal/slot by value. If somebody knows a better way of passing the QString and could show it to me, that'd be great.

That was fun though, now I start to get a hang of it, and I'm going to start adding features.

SerialPortReader.hpp

#pragma once
 
#include "CSerial.hpp"
#include <QString>
#include <QStringList>
#include <QThread>
 
class SerialPortReader : public QThread
{
	Q_OBJECT
 
public:
	SerialPortReader();
	void run();
 
signals:
	void newString( QString string );
 
private:
	QString*			str;
	QStringList*		list;
	CSerial*			port;
};

#pragma once

#include "CSerial.hpp"
#include <QString>
#include <QStringList>
#include <QThread>

class SerialPortReader : public QThread
{
	Q_OBJECT

public:
	SerialPortReader();
	void run();

signals:
	void newString( QString string );

private:
	QString*			str;
	QStringList*		list;
	CSerial*			port;
};

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SerialPortReader.cpp

#include "SerialPortReader.hpp"
 
#include <tchar.h>
#include <assert.h>
 
SerialPortReader::SerialPortReader()
{
	str  = new QString;
	list = new QStringList;
	port = new CSerial;	
 
	LONG stat;
 
	stat = port->Open( _T("COM1"), 0, 0, true );
	assert( stat == ERROR_SUCCESS );
 
	stat = port->Setup(	CSerial::EBaud115200,
						CSerial::EData8,
						CSerial::EParNone,
						CSerial::EStop1 );
	assert( stat == ERROR_SUCCESS );
 
	stat = port->SetupHandshaking( CSerial::EHandshakeOff );
	assert( stat == ERROR_SUCCESS );
 
	stat = port->SetupReadTimeouts( CSerial::EReadTimeoutBlocking );
	assert( stat == ERROR_SUCCESS );
 
}
 
void SerialPortReader::run()
{
	char data[100] = "Hey man how are you?";
 
	while(1)
	{
		int				charIdx = 0;
		DWORD			bytesRead;
 
		//
		// Find sync word
		do
		{
			data[charIdx] = 'A';
			port->Read( &data[charIdx],
						1,
						&bytesRead );
		} while( data[charIdx] != '$' );
		charIdx++;
 
		//
		// Read the rest of the data
		do
		{
			port->Read( &data[charIdx],
						1,
						&bytesRead );
			charIdx++;
		} while( data[charIdx-1] != '*' );
 
 
		//
		// Read check sum
		port->Read( &data[charIdx],
					2,
					&bytesRead );
		charIdx += 2;
		data[charIdx] = '\0';
 
		//
		// Copy buffer to QString
		*str = data;
 
		//
		// Indicate there's a new string
		emit newString( *str );
	}
}

#include "SerialPortReader.hpp"

#include <tchar.h>
#include <assert.h>

SerialPortReader::SerialPortReader()
{
	str  = new QString;
	list = new QStringList;
	port = new CSerial;	

	LONG stat;

	stat = port->Open( _T("COM1"), 0, 0, true );
	assert( stat == ERROR_SUCCESS );

	stat = port->Setup(	CSerial::EBaud115200,
						CSerial::EData8,
						CSerial::EParNone,
						CSerial::EStop1 );
	assert( stat == ERROR_SUCCESS );

	stat = port->SetupHandshaking( CSerial::EHandshakeOff );
	assert( stat == ERROR_SUCCESS );

	stat = port->SetupReadTimeouts( CSerial::EReadTimeoutBlocking );
	assert( stat == ERROR_SUCCESS );

}

void SerialPortReader::run()
{
	char data[100] = "Hey man how are you?";

	while(1)
	{
		int				charIdx = 0;
		DWORD			bytesRead;

		//
		// Find sync word
		do
		{
			data[charIdx] = 'A';
			port->Read( &data[charIdx],
						1,
						&bytesRead );
		} while( data[charIdx] != '$' );
		charIdx++;
			 
		//
		// Read the rest of the data
		do
		{
			port->Read( &data[charIdx],
						1,
						&bytesRead );
			charIdx++;
		} while( data[charIdx-1] != '*' );


		//
		// Read check sum
		port->Read( &data[charIdx],
					2,
					&bytesRead );
		charIdx += 2;
		data[charIdx] = '\0';

		//
		// Copy buffer to QString
		*str = data;

		//
		// Indicate there's a new string
		emit newString( *str );
	}
}

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GUI.hpp

#ifndef QTAPP_H
#define QTAPP_H
 
#include <QtGui/QMainWindow>
#include "ui_qtapp.h"
#include <QLabel>
#include <QString>
#include "SerialPortReader.hpp"
 
class QtApp : public QMainWindow
{
	Q_OBJECT
 
public:
	QtApp(QWidget *parent = 0, Qt::WFlags flags = 0);
 
private:
	Ui::QtAppClass		ui;
	SerialPortReader*	portThread;
 
public slots:
	void				DisplayString( QString string );
};
 
#endif // QTAPP_H

#ifndef QTAPP_H
#define QTAPP_H

#include <QtGui/QMainWindow>
#include "ui_qtapp.h"
#include <QLabel>
#include <QString>
#include "SerialPortReader.hpp"

class QtApp : public QMainWindow
{
	Q_OBJECT

public:
	QtApp(QWidget *parent = 0, Qt::WFlags flags = 0);

private:
	Ui::QtAppClass		ui;
	SerialPortReader*	portThread;

public slots:
	void				DisplayString( QString string );
};

#endif // QTAPP_H

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GUI.cpp

#include "qtapp.h"
 
QtApp::QtApp(QWidget *parent, Qt::WFlags flags)
	: QMainWindow(parent, flags)
{
	ui.setupUi(this);
 
	// Start a new thread
	portThread = new SerialPortReader;
 
	connect( portThread, SIGNAL(newString(QString)),
			 this,       SLOT(DisplayString(QString)) );
 
	portThread->start();
}
 
void QtApp::DisplayString( QString string )
{
	ui.mLabel->setText( string );
}

#include "qtapp.h"

QtApp::QtApp(QWidget *parent, Qt::WFlags flags)
	: QMainWindow(parent, flags)
{
	ui.setupUi(this);

	// Start a new thread
	portThread = new SerialPortReader;

	connect( portThread, SIGNAL(newString(QString)),
			 this,       SLOT(DisplayString(QString)) );

	portThread->start();
}

void QtApp::DisplayString( QString string )
{
	ui.mLabel->setText( string );
}

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UI Generated by Designer

class Ui_QtAppClass
{
public:
    QWidget *centralWidget;
    QLabel *mLabel;
    QStatusBar *statusBar;
 
    //....
 
}

class Ui_QtAppClass
{
public:
    QWidget *centralWidget;
    QLabel *mLabel;
    QStatusBar *statusBar;

    //....

}

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[marcel]

I can't see anywhere why you get those mem leaks... Maybe I'm missing something. Anyway, you should really add destructors to your classes and delete all the pointers you allocate. You will have some leaks in the thread class.

Anyway, why don't you just use a queue of qstrings instead of the single qstring (QQueue. You will pass a pointer to this QQueue to the main GUI, in the rest it is a standard producer/consumer scenario. The GUI thread takse QStrings of the top of the Queue, the worker thread appends them as soon as it gets them.

I realize now you can't pass a single QString pointer because it could get overwritten in the mean time, before it is displayed in the GUI.

Regards

[sar_van81]

ShaChris23:

can you say me how did you link the qextserial package to qt ? actually i'm trying to read the data's coming from the serial port.i found in the some forum posts that we can use qextserial package. i downloaded and compiled it for my linux PC also .but i could not figure how to use it with the qt. when i compiled it, i found only the libraries where created. In your code i found that you had added the header file "#include "qextserialport.h"" and created an object for qextserial. so i my code if i simply add the header will it work ? or should i place the library in some location in qt-embedded