Qt first project

nick784512

Thank you! I cannot understand how the tutorial video in youtube works and the same configuration and coding in my project does not work.

SGaist

Did you check that the settings of the serial ports are really what you need to use with your device ?

nick784512

@SGaist

1)How do I check if the serial opened succefully?
2)I disabled write.
3)Do you mean to make it private member of MainWindow?

SGaist

Please read the documentation, the open function returns a boolean value saying whether it succeeded or not
Where did you put the call to write ?
Yes

nick784512

@SGaist

1)Ok, I will try it.
2)I just commented it.
3) I wrote QSerialPort *serial; under private and it shows error

SGaist

What error ?

If you comment the call to write then don't expect anything particular to happen.

nick784512

@SGaist

C:\Users\geo\Documents\serialGui\mainwindow.h:27: error: 'QSerialPort' does not name a type
QSerialPort *serial;
^

I don't want to write something in COM from Qt, I want to "listen" from Arduino the sequence 232323... and print on the Qt application

SGaist

It's nothing Qt related, that's basic C++. You really should grab a good book on the matter.

Search for "Forward declaration".

nick784512

I know C, not C++. Are they so different?

SGaist

There are some key concepts that are pretty different yes.

nick784512

And I should learn C++ for just this little error?

Can someone help me to make it work?

nick784512

$$$$$$$$$$$$$$$$$$$$$serialGui.pro$$$$$$$$$$$$$$$$$$$$$$$$$$

#-------------------------------------------------

Project created by QtCreator 2016-12-06T15:42:10

#-------------------------------------------------

QT += core gui serialport

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = serialGui
TEMPLATE = app

SOURCES += main.cpp
mainwindow.cpp

HEADERS += mainwindow.h

FORMS += mainwindow.ui

$$$$$$$$$$$$$$$$$ mainwindow.h $$$$$$$$$$$$$$$$$$$$$$$$$$

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();

private slots:
void serialReceived();

void on_pushButton_released();

private:
Ui::MainWindow *ui;

QSerialPort *serial;

};

#endif // MAINWINDOW_H

$$$$$$$$$$$$$$$ main.cpp $$$$$$$$$$$$$$$$$$$$$$$$$

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();

return a.exec();

}

$$$$$$$$$$$$$$$$$$$$$$ mainwindow.cpp $$$$$$$$$$$$$$$$$$$$$$$$

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QtSerialPort>
#include <QDebug>

QSerialPort *serial;

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
if (serial->open(QIODevice::ReadWrite))
{
ui->setupUi(this);
serial = new QSerialPort(this);
serial->setPortName("COM3");
serial->setBaudRate(QSerialPort::Baud9600);
serial->setDataBits(QSerialPort::Data8);
serial->setParity(QSerialPort::NoParity);
serial->setStopBits(QSerialPort::OneStop);
serial->setFlowControl(QSerialPort::NoFlowControl);
serial->open(QIODevice::ReadWrite);
//serial->write("hello");
serial->close();
connect(serial,SIGNAL(readyRead()),this,SLOT(serialReceived()));
}
else
{
QMessageBox::critical(this, tr("Error"), serial->errorString());
showStatusMessage(tr("Open error"));
}
}

MainWindow::~MainWindow()
{
delete ui;
serial->close();
}

void MainWindow::serialReceived()
{
QByteArray ba;
ba=serial->readAll();
ui->label->setText(ba);
//qDebug()<<ba;
}

$$$$$$$$$$$$$$$$$$$ mainwindow.ui $$$$$$$$$$$$$$$$$$$$$$$$$$

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>400</width>
<height>300</height>
</rect>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<widget class="QWidget" name="centralWidget">
<widget class="QLabel" name="label">
<property name="geometry">
<rect>
<x>50</x>
<y>60</y>
<width>121</width>
<height>41</height>
</rect>
</property>
<property name="text">
<string>TextLabel</string>
</property>
</widget>
</widget>
<widget class="QMenuBar" name="menuBar">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>400</width>
<height>21</height>
</rect>
</property>
</widget>
<widget class="QToolBar" name="mainToolBar">
<attribute name="toolBarArea">
<enum>TopToolBarArea</enum>
</attribute>
<attribute name="toolBarBreak">
<bool>false</bool>
</attribute>
</widget>
<widget class="QStatusBar" name="statusBar"/>
</widget>
<layoutdefault spacing="6" margin="11"/>
<resources/>
<connections/>
</ui>

JKSH

@nick784512 said in Qt first project:

And I should learn C++ for just this little error?

You should learn C++ to use a C++ toolkit.

It feels like a "little error" now, but you will encounter this in most (if not all) of your C++ projects.

Can someone help me to make it work?

@SGaist already gave you the answer: You need to add a Forward Declaration for QSerialPort in mainwindow.h.

Also remember to #include <QSerialPort> in mainwindow.cpp

nick784512

Hello!

I managed to make it work and send symbols over the serial. The problem now is that when I send from the arduino (to Qt application) 2 or 3 symbols it prints them OK! But when I want to send the sentence "Hello World!" it breaks it into pieces and prints them, as you can see in the photo.

http://www.picpaste.com/pics/serial_problem-V7LlwzUC.1483458098.jpg

(Can the moderator attach the photo to this message?)

SGaist

That' why you usually have a protocol to know when you received all the data that are part of a "frame" and only then parse them for further processing.

nick784512

How I do this? I think of using a "flag" that when the Qt application reads it, then prints the sentence. Right? For example "Hello World!#" and when it reads the "#", it prints the "Hello World!". Am I correct?

SGaist

More or less, yes.

You buffer the data you can read when readyRead is emitted and once you find your # you take the amount of data needed from the buffer and do whatever you want with it.

nick784512

For buffer is better to use an array or a data structure? List for example and each node to save a letter? Is there a source code to study?

SGaist

Don't over-engineer it, just use a QByteArray.

nick784512

I use an array with a fixed length that when it become full I read it, or an array with dynamic length?