Data sharing problem between threads in Qt QML backend C++ - c++

I am newbie in Qt/QML world and i am trying a multithread application. I have 2 threads. I want to pass some value from one thread to another but i have a problem with it. I can see the value from setValue() function but i cannot see the value from the showData() thread of the same object. My code is below:
My object changes the value in doWork thread
class MyObject : public QObject
{
Q_OBJECT
public:
myWorker *itsMyWorker;
explicit MyObject(QObject *parent = nullptr){
itsMyWorker= new myWorker;
}
void doSetup(QThread &cThread){
connect(&cThread, SIGNAL(started()), this, SLOT(doWork()));
}
signals:
public slots:
void doWork(){
for(int i = 0; i < 100; i++){
if(i % 10 == 0)
itsMyWorker->setValue(i);
}
}
};
I want to see the value from showData thread
class myWorker : public QObject
{
Q_OBJECT
public:
explicit myWorker (QObject *parent = nullptr);
void doSetup(QThread &cThread){
connect(&cThread, SIGNAL(started()), this, SLOT(showData()));
}
void setValue(int i){
myNumber = Number;
qDebug() << "setValue() " << myNumber;
}
void showValue(){
//qDebug() << "showValue() " << myNumber;
}
signals:
public slots:
void showData(){
while(1){
showValue();
}
}
private:
int myNumber;
};
And this is the main
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QThread>
#include "myobject.h"
#include "mynesne.h"
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QThread cThread;
MyObject cObject;
cObject.doSetup(cThread);
cObject.moveToThread(&cThread);
QThread cThread2;
myWorker cWorker;
cWorker.doSetup(cThread2);
cWorker.moveToThread(&cThread2);
cThread2.start();
cThread.start();
QQmlApplicationEngine engine;
const QUrl url(QStringLiteral("qrc:/main.qml"));
QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
&app, [url](QObject *obj, const QUrl &objUrl) {
if (!obj && url == objUrl)
QCoreApplication::exit(-1);
}, Qt::QueuedConnection);
engine.load(url);
return app.exec();
}

Related

QT Serialport GUI and worker thread

First things first, I'm a newbie in QT so don't blame me. I know that many similar questions have been in the forum, but I couldn't solve my problem.
Problem description. I want to have a GUI application that receives and parses data and update some qt widget. Formerly I did them all in the Mainwindow thread, but since it hangs, I tried to make it multi-threaded. But it still hangs when I try to update GUI data as fast as 10 ms.
Now, this is what I have tried.
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
class Parser : public QThread , public QRunnable
{
Q_OBJECT
public:
explicit Parser(QThread *parent = nullptr);
~Parser();
signals:
void data1Available(unsigned char*);
void data2Available(unsigned char*);
void finished();
// QRunnable interface
public:
void run();
public slots:
void parse();
};
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect( &SerialPort, SIGNAL(readyRead()), this, SLOT(ReadData()) );
QThread* thread = new QThread;
thread->setObjectName("Parser Thread");
qInfo()<<"Parser Thread";
Parser* parser= new Parser();
parser->moveToThread(thread);
QObject::connect(thread,&QThread::started,parser,&Parser::run);
QObject::connect(parser,&Parser::finished,parser,&Parser::deleteLater);
QObject::connect(parser,&Parser::finished,thread,&QThread::quit);
QObject::connect(thread,&QThread::finished,thread,&QThread::deleteLater);
QObject::connect(parser,SIGNAL(data1Available(unsigned char *)),this,SLOT(on_data1Available(unsigned char *)));
QObject::connect(parser,SIGNAL(data2Available(unsigned char *)),this,SLOT(on_data2Available(unsigned char *)));
thread->start();
}
void MainWindow::ReadData()
{
QByteArray Data = SerialPort.readAll();
for (unsigned char i=0;i<Data.length();i++)
circBuff.append(Data[i]);
}
void MainWindow::on_data1Available(unsigned char* tempData)
{
ui->label1->setNum(tempData[5]);
}
void MainWindow::on_data2Available(unsigned char* tempData)
{
ui->label2->setNum(tempData[7]);
}
void Parser::run()
{
qInfo()<<this<<Q_FUNC_INFO<<QThread::currentThread();
QScopedPointer<QEventLoop> loop (new QEventLoop);
QScopedPointer<QTimer> timer (new QTimer);
timer->setInterval(5);
connect(timer.data(),&QTimer::timeout,this,&Parser::parse);
connect(this,&Parser::finished,loop.data(),&QEventLoop::quit);
timer->start();
loop->exec();
qInfo()<<this<<"Finished... "<<QThread::currentThread();
}
void Parser::parse()
{
unsigned char tempData[16];
while (1)
{
while (circBuff.size()>=16)
{
if ( )
{
if ()
emit data1Available(tempData);
else
emit data2Available(tempData);
}
}
}
emit finished();
}

How is a QList of QString assigned to a list view?

I wrote this database front-end program with Qt and I used a C++ function to return the result of each query. However, I'm not able to assign the results to a list view.
MyObject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <QObject>
class MyObject : public QObject
{
Q_OBJECT
Q_PROPERTY(QList<QString> val READ val WRITE setVal NOTIFY valChanged)
public:
void setVal(QList<QString>);
QList<QString> val() const;
explicit MyObject(QObject *parent = nullptr);
Q_INVOKABLE int registernew(int Sno=0, QString Name="NULL",long long PhoneNo=0, QString Country="NULL",QString State="NULL", QString District="NULL", int PhoneLine=0,long long Whatsapp = 0);
Q_INVOKABLE int querydistrict(QString);
signals:
void valChanged();
private:
QList<QString> m_val;
};
#endif // MYOBJECT_H
MyObject.cpp
.............. void MyObject::setVal(QList<QString> list)
{
if(list != m_val)
{
m_val = list;
emit valChanged();
}
}
QList<QString> MyObject::val() const
{
return m_val;
}....................
main.cpp
#include <QGuiApplication>
#include<QQmlApplicationEngine>
#include "myobject.h"
#include<QQuickView>
#include<QQmlContext>
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
///delete later!!
qmlRegisterType<MyObject>("io.qt.examples.MyObject", 1, 0, "MyObject");
const QUrl url(QStringLiteral("qrc:/main.qml"));
QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
&app, [url](QObject *obj, const QUrl &objUrl) {
if (!obj && url == objUrl)
QCoreApplication::exit(-1);
}, Qt::QueuedConnection);
engine.load(url);
return app.exec();
}
page2.ui.qml
ScrollView {
id: scrollView
anchors.rightMargin: 20
anchors.leftMargin: 20
anchors.bottomMargin: 40
anchors.topMargin: 200
anchors.fill: parent
ListView {
id: listView
model: myobject.val
delegate: ItemDelegate {
text: modelData
}
}
}
Where am i going wrong? The list is never updated with values when i run the program. It is always blank. But the variable m_val, when I return it in MyObject.cpp and use qDebug to output it, outputs relevant strings.
You should not use QList<QString> but QStringList as it is registered. On the other hand if you are going to establish the data from C ++ since you indicate that it is the result of a query then that Q_PROPERTY is not of being written in QML. Finally, although it is not an error, it is better to register the classes before creating the QXApplication.
myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <QObject>
class MyObject : public QObject
{
Q_OBJECT
Q_PROPERTY(QStringList val READ val NOTIFY valChanged)
public:
explicit MyObject(QObject *parent = nullptr);
QStringList val() const;
void setVal(QStringList val);
// other methods
signals:
void valChanged(QStringList val);
private:
QStringList m_val;
};
#endif // MYOBJECT_H
myobject.cpp
#include "myobject.h"
// other methods
QStringList MyObject::val() const{
return m_val;
}
void MyObject::setVal(QStringList val)
{
if (m_val == val)
return;
m_val = val;
emit valChanged(m_val);
}
main.cpp
// ...
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
qmlRegisterType<MyObject>("io.qt.examples.MyObject", 1, 0, "MyObject");
QGuiApplication app(argc, argv);
// ...
So when you do your query you must pass the result to setVal:
setVal(your_QStringList);

Redirecting std::cout from DLL in a separate thread to QTextEdit

The goal is to display all the application output shown in QtCreator to a QTextEdit as a debug console window so with the same application only those who have password are allowed to see the console window while normal users cannot. There is an exe with several dlls. All std::cout from DLLs and qDebug are needed to be shown in the debug console window.
To achieve this, I have followed
http://www.qtforum.org/article/39768/redirecting-std-cout-std-cerf-qdebug-to-qtextedit.html
The code works great for single thread but is hanged when a thread is started to call functions in DLL. I would like to know how to fix the problem.
code
In mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QObject>
#include <QThread>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
m_qd = new Q_DebugStream(std::cout,ui->textEdit); //Redirect Console output to QTextEdit
m_qd->Q_DebugStream::registerQDebugMessageHandler(); //Redirect qDebug() output to QTextEdit
connect(ui->pushButtonSingleThreadTest, SIGNAL(clicked()),this,SLOT(SingleThreadTest()));
connect(ui->pushButtonMultiThreadTest, SIGNAL(clicked()),this,SLOT(MultiThreadTest()));
}
void MainWindow::SingleThreadTest()
{
run();
}
void MainWindow::MultiThreadTest()
{
QThread *workerThread= new QThread;
ThreadWorker *worker = new ThreadWorker();
worker->moveToThread(workerThread);
connect(workerThread, SIGNAL(started()), worker, SLOT(doWork()));
connect(worker, SIGNAL(finished()), workerThread, SLOT(quit()));
connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
connect(workerThread, SIGNAL(finished()), workerThread, SLOT(deleteLater()));
workerThread->start();
}
MainWindow::~MainWindow()
{
delete ui;
}
In mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include "q_debugstream.h"
#include "../ToyProj1/Header.h"
namespace Ui {
class MainWindow;
}
class ThreadWorker : public QObject
{
Q_OBJECT
public:
ThreadWorker()
{
}
private:
signals:
void finished();
public slots:
void doWork()
{
run();
emit finished();
}
};
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
public slots:
void SingleThreadTest();
void MultiThreadTest();
private:
Ui::MainWindow *ui;
Q_DebugStream* m_qd;
};
#endif // MAINWINDOW_H
in q_debugstream.h
#ifndef Q_DEBUGSTREAM_H
#define Q_DEBUGSTREAM_H
#include <iostream>
#include <streambuf>
#include <string>
#include "QTextEdit.h"
class Q_DebugStream : public std::basic_streambuf<char>
{
public:
Q_DebugStream(std::ostream &stream, QTextEdit* text_edit) : m_stream(stream)
{
log_window = text_edit;
m_old_buf = stream.rdbuf();
stream.rdbuf(this);
}
~Q_DebugStream()
{
m_stream.rdbuf(m_old_buf);
}
static void registerQDebugMessageHandler(){
qInstallMessageHandler(myQDebugMessageHandler);
}
private:
static void myQDebugMessageHandler(QtMsgType, const QMessageLogContext &, const QString &msg)
{
std::cout << msg.toStdString().c_str();
}
protected:
//This is called when a std::endl has been inserted into the stream
virtual int_type overflow(int_type v)
{
if (v == '\n')
{
log_window->append("");
}
return v;
}
virtual std::streamsize xsputn(const char *p, std::streamsize n)
{
QString str(p);
if(str.contains("\n")){
QStringList strSplitted = str.split("\n");
log_window->moveCursor (QTextCursor::End);
log_window->insertPlainText (strSplitted.at(0)); //Index 0 is still on the same old line
for(int i = 1; i < strSplitted.size(); i++){
log_window->append(strSplitted.at(i));
}
}else{
log_window->moveCursor (QTextCursor::End);
log_window->insertPlainText (str);
}
return n;
}
private:
std::ostream &m_stream;
std::streambuf *m_old_buf;
QTextEdit* log_window;
};
#endif // Q_DEBUGSTREAM_H
In DLL,
int run()
{
std::cout << "Hello World" << std::endl;
return 0;
}
The code sample is uploaded to github for reference. Build ToyProj1 and ToyProj1GUI when repeat the problem.
https://github.com/kuwt/ToyProject.git
With the help comments in question, this solution works well with signal and slot mechanism. std::cout and qDebug are redirected to QTextEdit.
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
// Setup QMessageCatch
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
qInstallMessageHandler(MainWindow::QMessageOutput);
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
return a.exec();
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QDebug>
#include <QTextEdit>
#include "q_debugstream.h"
namespace Ui {
class MainWindow;
}
class ThreadWorker : public QObject
{
Q_OBJECT
public:
ThreadWorker()
{
}
private:
signals:
void finished();
public slots:
void doWork()
{
std::cout<< "Hello World2" <<std::endl;
qDebug() << "Hello World2q" ;
emit finished();
}
};
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
// QMessage
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
static void QMessageOutput(QtMsgType , const QMessageLogContext &, const QString &msg);
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
public slots:
void SingleThreadTest();
void MultiThreadTest();
private:
Ui::MainWindow *ui;
// MessageHandler for display and ThreadLogStream for redirecting cout
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
MessageHandler *msgHandler = Q_NULLPTR;
ThreadLogStream* m_qd;
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QObject>
#include <QThread>
// Catch QMessage, redirect to cout
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
void MainWindow::QMessageOutput(QtMsgType , const QMessageLogContext &, const QString &msg)
{
std::cout<<msg.toStdString().c_str()<<std::endl;
}
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
// Set up ThreadLogStream, which redirect cout to signal sendLogString
// Set up MessageHandler, wgucg catch message from sendLogString and Display
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
m_qd = new ThreadLogStream(std::cout); //Redirect Console output to QTextEdit
this->msgHandler = new MessageHandler(this->ui->textEdit, this);
connect(m_qd, &ThreadLogStream::sendLogString, msgHandler, &MessageHandler::catchMessage);
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
connect(ui->pushButtonSingleThreadTest, SIGNAL(clicked()),this,SLOT(SingleThreadTest()));
connect(ui->pushButtonMultiThreadTest, SIGNAL(clicked()),this,SLOT(MultiThreadTest()));
}
void MainWindow::SingleThreadTest()
{
std::cout<< "Hello World1" <<std::endl;
qDebug() << "Hello World1q" ;
}
void MainWindow::MultiThreadTest()
{
QThread *workerThread= new QThread;
ThreadWorker *worker = new ThreadWorker();
worker->moveToThread(workerThread);
connect(workerThread, SIGNAL(started()), worker, SLOT(doWork()));
connect(worker, SIGNAL(finished()), workerThread, SLOT(quit()));
connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
connect(workerThread, SIGNAL(finished()), workerThread, SLOT(deleteLater()));
workerThread->start();
}
MainWindow::~MainWindow()
{
delete ui;
}
q_debugstream.h
#ifndef ThreadLogStream_H
#define ThreadLogStream_H
#include <iostream>
#include <streambuf>
#include <string>
#include <QScrollBar>
#include "QTextEdit"
#include "QDateTime"
// MessageHandler
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
class MessageHandler : public QObject
{
Q_OBJECT
public :
MessageHandler(QTextEdit *textEdit, QObject * parent = Q_NULLPTR) : QObject(parent), m_textEdit(textEdit){}
public slots:
void catchMessage(QString msg)
{
this->m_textEdit->append(msg);
}
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
private:
QTextEdit * m_textEdit;
};
/*!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
class ThreadLogStream : public QObject, public std::basic_streambuf<char>
{
Q_OBJECT
public:
ThreadLogStream(std::ostream &stream, QObject * parent = Q_NULLPTR) :QObject(parent), m_stream(stream)
{
m_old_buf = stream.rdbuf();
stream.rdbuf(this);
}
~ThreadLogStream()
{
// output anything that is left
if (!m_string.empty())
{
emit sendLogString(QString::fromStdString(m_string));
}
m_stream.rdbuf(m_old_buf);
}
protected:
virtual int_type overflow(int_type v)
{
if (v == '\n')
{
emit sendLogString(QString::fromStdString(m_string));
m_string.erase(m_string.begin(), m_string.end());
}
else
m_string += v;
return v;
}
virtual std::streamsize xsputn(const char *p, std::streamsize n)
{
m_string.append(p, p + n);
long pos = 0;
while (pos != static_cast<long>(std::string::npos))
{
pos = static_cast<long>(m_string.find('\n'));
if (pos != static_cast<long>(std::string::npos))
{
std::string tmp(m_string.begin(), m_string.begin() + pos);
emit sendLogString(QString::fromStdString(tmp));
m_string.erase(m_string.begin(), m_string.begin() + pos + 1);
}
}
return n;
}
private:
std::ostream &m_stream;
std::streambuf *m_old_buf;
std::string m_string;
signals:
void sendLogString(const QString& str);
};
#endif // ThreadLogStream_H
for long transactions, you can add:
QCoreApplication::processEvents();
in the catchMessage(QString(msg) method of the class MessageHandler in q_debugstream.h, after the append() call.
This updates textEdit 'as soon as possible'.

Qt - Simple example using threads controlled by push buttons

I have been trying to get this simple example using threads activated by pushbuttons to work. It is based off of the solution in the question below:
How to implement frequent start/stop of a thread (QThread)
The main differences between the example solution above and my code below are:
I used a QWidget instead of MainWindow
I changed the name of signals for clarity
My code contains debugging information
I experimented with eliminating the signals created by worker as the didn't appear to do anything
It appears that the start/stop signals are not triggering their corresponding slots, but I am not experienced enough to troubleshoot why.
Additionally, I am unsure of the purpose of the signal:
SignalToObj_mainThreadGUI()
Is that just something that could be used and is not?
I have been trying to get this code to work for some time, so any help would be greatly appreciated.
main.cpp
#include "threadtest.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
ThreadTest w;
w.show();
return a.exec();
}
threadtest.h
#include <QWidget>
#include <QThread>
#include "worker.h"
namespace Ui
{
class ThreadTest;
}
class ThreadTest : public QWidget
{
Q_OBJECT
public:
explicit ThreadTest(QWidget *parent = 0);
~ThreadTest();
signals:
void startWorkSignal();
void stopWorkSignal();
private slots:
void on_startButton_clicked();
void on_stopButton_clicked();
private:
Ui::ThreadTest *ui;
worker *myWorker;
QThread *WorkerThread;
};
threadtest.cpp
#include "threadtest.h"
#include "ui_threadtest.h"
ThreadTest::ThreadTest(QWidget *parent) :
QWidget(parent),
ui(new Ui::ThreadTest)
{
ui->setupUi(this);
myWorker = new worker;
WorkerThread = new QThread;
myWorker->moveToThread(WorkerThread);
connect(this,
SIGNAL(startWorkSignal()),
myWorker,
SLOT(StartWork())
);
connect(this,
SIGNAL(stopWorkSignal()),
myWorker,
SLOT(StopWork())
);
//Debug
this->dumpObjectInfo();
myWorker->dumpObjectInfo();
}
ThreadTest::~ThreadTest()
{
delete ui;
}
void ThreadTest::on_startButton_clicked()
{
qDebug() << "startwork signal emmitted";
emit startWorkSignal();
}
void ThreadTest::on_stopButton_clicked()
{
qDebug() << "stopwork signal emmitted";
emit stopWorkSignal();
}
worker.h
#include <QObject>
#include <QDebug>
class worker : public QObject {
Q_OBJECT
public:
explicit worker(QObject *parent = 0);
~worker();
signals:
void SignalToObj_mainThreadGUI();
//void running();
//void stopped();
public slots:
void StopWork();
void StartWork();
private slots:
void do_Work();
private:
volatile bool running, stopped;
};
worker.cpp
#include "worker.h"
worker::worker(QObject *parent) : QObject(parent), stopped(false),
running(false)
{
qDebug() << "running: " << running;
qDebug() << "stopped: " << stopped;
}
worker::~worker() {}
void worker::do_Work()
{
qDebug() << "inside do Work";
emit SignalToObj_mainThreadGUI();
if (!running || stopped) return;
// actual work here
/*
for (int i = 0; i < 100; i++)
{
qDebug() << "count: " + i;
}
*/
QMetaObject::invokeMethod(this, "do_Work", Qt::QueuedConnection);
}
void worker::StopWork()
{
qDebug() << "inside StopWork";
stopped = true;
running = false;
//emit stopped();
}
void worker::StartWork()
{
qDebug() << "inside StartWork";
stopped = false;
running = true;
//emit running();
do_Work();
}
You should write
WorkerThread->start();
Or you can use the thread of the ThreadTest object instead the WorkerThread (in this case the WorkerThread is needless):
myWorker->moveToThread(thread()); // this->thread
The slots are not triggered, because you have moved myWork to the thread WorkerThread, but didnot run an event loop in that thread. In threadtest.cpp, add
WorkerThread .start();
after
myWorker = new worker;
WorkerThread = new QThread;
myWorker->moveToThread(WorkerThread);

Scope issues with Qt Quick and C++ classes

I have a project that I am working on, that will hopefully result in C++ code with a QML UI as a console, communicating with other consoles and equipment.
My test setup is based on a RaspBerry Pi running UDP comms (works fine into a normal Qt application).
I have tried to port to Qt Quick, and use a simple QML UI, but if I declare the subclass early in my "main.cpp" it doesn't connect properly.
If I declare it in the main.cpp "main" function, then I have scope issues with the subclass functions that I want to use to transfer data.
Open to suggestions / critique......and I am 100% sure that there is a "proper" way of doing this, so if anyone wants to point me at it......I will be enraptured!
Qt version is Qt5.3.
import QtQuick 2.2
import QtQuick.Controls 1.1
Rectangle {
width: 440; height: 150
color: "orange"
Column {
anchors.fill: parent; spacing: 20
Text {
text: rootItem.theChange
font.pointSize: 12; anchors.horizontalCenter: parent.horizontalCenter
}
}
}
// signalgrab.h
#ifndef SIGNALGRAB_H
#define SIGNALGRAB_H
#include <QObject>
#include <QUdpSocket>
#include <QString>
class SignalGrab : public QObject
{
Q_OBJECT
public:
explicit SignalGrab(QObject *parent = 0);
int SendValue();
void setupUDP();
signals:
public slots:
void readyRead();
private:
QUdpSocket *socket;
QHostAddress groupAddress;
};
#endif // SIGNALGRAB_H
// signalgrab.cpp
#include "signalgrab.h"
int i3 = 0;
SignalGrab::SignalGrab(QObject *parent) :
QObject(parent)
{
// create a QUDP socket
socket = new QUdpSocket(this);
socket->bind(QHostAddress("0.0.0.0"), 45454);
connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()));
qDebug() << "Socket connected ok!";
}
void SignalGrab::readyRead()
{
// when data comes in
QByteArray buffer;
buffer.resize(socket->pendingDatagramSize());
QHostAddress sender;
quint16 senderPort;
socket->readDatagram(buffer.data(), buffer.size(),
&sender, &senderPort);
std::string s1 (buffer);
std::string s2 = s1.substr(26,sizeof(s1));
i3 = atoi(s2.data());
SendValue();
}
int SignalGrab::SendValue()
{
qDebug() << "sending i3 as: "<< i3;
return i3;
}
// main.cpp
#include <QtGui>
#include <QApplication>
#include <QQmlContext>
#include <QQuickView>
#include <QString>
#include "signalgrab.h"
int y=13;
// ///////////////////////////////////
//SignalGrab nc;
// ///////////////////////////////////
class Object : public QObject
{
Q_OBJECT
Q_PROPERTY(QString theChange READ getTheChange NOTIFY changeOfStatus)
public:
Object()
{
changeMe = false;
myTimer = new QTimer(this);
myTimer->start(5000);
connect(myTimer, SIGNAL(timeout()), this, SLOT(testSlot()));
}
QString getTheChange()
{
if (theValue == 0)
{
return "The Acid QML Test";
}
if (theValue == 1)
{
y = (fetchValue());
qDebug() << "New y!" << y;
return QString("Returning %1").arg(y);
}
return "nothing has happened yet";
}
int fetchValue()
{
// return (nc::SendValue());
return y;
}
Q_INVOKABLE void someFunction(int i)
{
if ( i == 0) {
theValue = 0;
}
if (i == 1) {
theValue = 1;
}
emit changeOfStatus(i);
}
signals:
void changeOfStatus(int i) ;
public slots:
void testSlot()
{
if (changeMe)
{
someFunction(0);
} else {
someFunction(1);
}
changeMe = !changeMe;
}
private:
bool changeMe;
int theValue;
QTimer *myTimer;
};
#include "main.moc"
int main(int argc, char** argv)
{
QApplication app(argc, argv);
Object myObj;
// //////////////////////////////
SignalGrab nc; //added
// //////////////////////////////
nc.SendValue();
QQuickView view;
view.rootContext()->setContextProperty("rootItem", (QObject *)&myObj);
view.setSource(QUrl::fromLocalFile("main.qml"));
view.show();
return app.exec();
}