I'm trying to get the position updates in QCoreApplication, Following is the code i'm trying but i'm getting error as
QObject::connect: Cannot connect (null)::positionUpdated(QGeoPositionInfo) to QObject::positionUpdated(QGeoPositionInfo)
Code:
#include <QCoreApplication>
#include <QDebug>
#include <QObject>
#include <QtCore>
class MyClass : public QObject
{
// Q_OBJECT
public:
MyClass(QObject *parent = 0)
: QObject(parent)
{
qDebug() << "In class";
QGeoPositionInfoSource *source = QGeoPositionInfoSource::createDefaultSource(this);
qDebug() << source;
connect(source, SIGNAL(positionUpdated(QGeoPositionInfo)),
this, SLOT(positionUpdated(QGeoPositionInfo)));
source->startUpdates();
}
private slots:
void positionUpdated(const QGeoPositionInfo &info)
{
qDebug() << "Position updated:" << info;
}
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
qDebug("Qt running !");
MyClass *objmyclass = new MyClass;
return a.exec();
}
If i uncomment the Q_OBJECT i get error as:
:-1: error: the vtable symbol may be undefined because the class is missing its key function
Related
I need to assign a pointer to a custom class in qml using QQmlContext::setContextProperty(). Another qml object has Q_PROPERTY of the same type to retrieve it again.
A simple test showed me that the conversion does not work like i thought.
#include <QCoreApplication>
#include <QDebug>
#include <QMetaType>
class TestClass
{
public: TestClass() { qDebug() << "TestClass()::TestClass()"; }
};
Q_DECLARE_METATYPE(TestClass*)
int main(int argc, char *argv[])
{
QCoreApplication app(argc, argv);
qDebug() << "metaTypeId =" << qMetaTypeId<TestClass*>();
auto testObject = new TestClass;
QVariant variant(qMetaTypeId<TestClass*>(), testObject);
auto test = variant.value<TestClass*>();
qDebug() << testObject << variant << test;
return 0;
}
This tiny test application gives me an output like this:
metaTypeId = 1024
TestClass::TestClass()
0x1b801e0 QVariant(TestClass*, ) 0x0
I would really like to get the same pointer out again after converting it down to a QVariant. Later I will assign it to a qml context and then the conversation must work correctly.
This works for me using Qt 5.9:
#include <QVariant>
#include <QDebug>
class CustomClass
{
public:
CustomClass()
{
}
};
Q_DECLARE_METATYPE(CustomClass*)
class OtherClass
{
public:
OtherClass()
{
}
};
Q_DECLARE_METATYPE(OtherClass*)
int main()
{
CustomClass *c = new CustomClass;
OtherClass *o = new OtherClass;
QVariant v;
v.setValue(c);
QVariant v2;
v2.setValue(o);
qDebug() << v.userType() << qMetaTypeId<CustomClass*>() << v2.userType() << qMetaTypeId<OtherClass*>();
qDebug() << v.value<CustomClass*>() << c << v2.value<OtherClass*>() << o;
return 0;
}
And the output i got:
1024 1024 1025 1025
0x81fca50 0x81fca50 0x81fca60 0x81fca60
As #thuga mentioned in the comments, you need to use void* and static_cast along with QVariant::fromValue.
#include <QCoreApplication>
#include <QDebug>
#include <QMetaType>
class TestClass
{
public: TestClass() { qDebug() << "TestClass()::TestClass()"; }
};
Q_DECLARE_METATYPE(TestClass*)
int main(int argc, char *argv[])
{
QCoreApplication app(argc, argv);
qDebug() << "metaTypeId =" << qMetaTypeId<TestClass*>();
auto testObject = new TestClass;
QVariant variant(QVariant::fromValue(static_cast<void*>(testObject)));
auto test = static_cast<TestClass*>(variant.value<void*>());
qDebug() << testObject << variant << test;
return 0;
}
I'm totaly new in QT programming so i got a bit noob question.
Why I get this error?
undefined reference to `Messenger::newParticipant(QString)'
main.cpp
#include <QCoreApplication>
#include <QTextStream>
#include "messenger.h"
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
Messenger* messenger = new Messenger();
messenger->newParticipant("AAAA");
QTextStream qout(stdout);
qout << "asd\n";
qout.flush();
return a.exec();
}
messenger.h
#ifndef MESSENGER_H
#define MESSENGER_H
#include "network/client.h"
#include <iostream>
#include <QTextStream>
class Messenger
{
public:
Messenger();
void newParticipant(const QString &nick);
private slots:
void sendMessage(const QString &message);
void participantLeft(const QString &nick);
};
#endif // MESSENGER_H
messenger.cpp
#include "messenger.h"
Messenger::Messenger()
{
QTextStream qout(stdout);
qout << "a. Constructor...\n";
qout.flush();
}
void newParticipant(const QString &nick)
{
if (nick.isEmpty())
return;
QTextStream qout(stdout);
qout << nick;
qout.flush();
}
You forgot to specify classname in definition of newParticipant.
Try to change it to void Messenger::newParticipant(const QString &nick) in messenger.cpp.
That's because you forgot to write Messenger:: before newParticipant definition in your cpp file.
I observed that through task mgr, the memory increases in steps of 4kB and 8kB, though not necessarily in this order.
Possible duplicate: Windows Task Manager shows process memory keeps growing even though there are no memory leaks
I am not sure whether this's occurring because I did not release the QTimer object, timer2. Please advise me how to stop this memory increase, and whether my guess of why it's occurring, is correct.
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QtCore>
#include <QDebug>
#include <QDateTime>
#include <QFileInfo>
#include <QString>
#include <opencv/cv.h>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#define TIMER2_VALUE 3000
#define UPDATED_IMAGE_STORAGE_PATH "E:\\QT1\\timeStampDateMod2\\TimeStampDateMod2\\updatedRefImg.JPG"
#define UPDATED_IMAGE_BACKUP_PATH "E:\\QT1\\timeStampDateMod2\\TimeStampDateMod2\\backUp\\updatedRefImg[%1].JPG"
using namespace std;
using namespace cv;
typedef struct
{
QDateTime dateTimeMod1;
QDateTime dateTimeMod2;
}tTimeMods;
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
QTimer *timer2;
tTimeMods findTimeModifiedStruct();
QDateTime findTimeModified();
void compareTimeMods(tTimeMods timeTypeFunction, QDateTime dateTimeMod2);
QString appendWithImageName(tTimeMods timeTypeFunction);
void shiftToRepository(QString pathString);
void updatedImgToRepository(QString pathString);
public slots:
void timerSlot2();
private:
Ui::MainWindow *ui;
};
#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"
tTimeMods timeTypeFunction, timeTypeMain;
QDateTime dateTimeMod2;
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
timeTypeMain = findTimeModifiedStruct();
timer2 = new QTimer(this);
connect(timer2, SIGNAL(timeout()), this, SLOT(timerSlot2()));
timer2->start(TIMER2_VALUE);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::timerSlot2()
{
dateTimeMod2 = findTimeModified();
compareTimeMods(timeTypeMain, dateTimeMod2);
//delete timer2;
}
//tTimeMods findTimeModifiedStruct()
tTimeMods MainWindow::findTimeModifiedStruct()
{
QString myFileName = UPDATED_IMAGE_STORAGE_PATH;
QFileInfo info(myFileName);
/*find last date modified*/
timeTypeFunction.dateTimeMod1 = info.lastModified();
timeTypeFunction.dateTimeMod2 = info.lastModified();
qDebug()<< "dateTimeMod1: " << timeTypeFunction.dateTimeMod1.toString() << endl << "dateTimeMod2: "<< timeTypeFunction.dateTimeMod2.toString();
return(timeTypeFunction);
}
QDateTime MainWindow::findTimeModified()
{
QString myFileName = UPDATED_IMAGE_STORAGE_PATH;
QFileInfo info(myFileName);
QDateTime dateTimeMod2 = info.lastModified();
qDebug()<< "dateTimeMod2: "<< dateTimeMod2.toString();
return(dateTimeMod2);
}
void MainWindow::compareTimeMods(tTimeMods timeTypeFunction, QDateTime dateTimeMod2)
{
if(dateTimeMod2 >= timeTypeFunction.dateTimeMod1)
{
timeTypeFunction.dateTimeMod1 = dateTimeMod2;
QString pathString = appendWithImageName(timeTypeFunction);
shiftToRepository(pathString);
}
}
QString MainWindow::appendWithImageName(tTimeMods timeTypeFunction)
{
/*appending just the timeMod with the path & image name*/
QString path = QString(UPDATED_IMAGE_BACKUP_PATH).arg(timeTypeFunction.dateTimeMod1.toString());
qDebug()<< "path: " << path;
return path;
}
void MainWindow::shiftToRepository(QString pathString)
{
updatedImgToRepository(pathString);
}
void MainWindow::updatedImgToRepository(QString pathString)
{
pathString.replace(":","-");
pathString.replace(1,1,":");
qDebug()<<"pathString now: "<<pathString;
/*convert QString into char* */
QByteArray pathByteArray = pathString.toLocal8Bit();
const char *path = pathByteArray.data();
IplImage *InputImg = cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,3);
InputImg = cvLoadImage(UPDATED_IMAGE_STORAGE_PATH ,CV_LOAD_IMAGE_UNCHANGED);
/*save the image*/
cvSaveImage(path,InputImg);
cvReleaseImage(&InputImg);
}
I'm not familiar with OpenCV, but it seems that these two lines cause you memory leak:
IplImage *InputImg = cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,3);
InputImg = cvLoadImage(UPDATED_IMAGE_STORAGE_PATH ,CV_LOAD_IMAGE_UNCHANGED);
In the first line you are creating an object, but in the second you are assigning another object to the pointer without releasing the previous one, so the previous one gets leaked.
Is creating an image even needed, while you are going to load it?
i am playing with Exposing Attributes of C++ Types to QML in Qt5 based on this tutor http://qt-project.org/doc/qt-5.0/qtqml/qtqml-cppintegration-exposecppattributes.html. when i run it i got this error on my issues pane error: variable 'QQmlComponent component' has initializer but incomplete type not only i have this error i have also this error the signal i have created using Q_PROPERTY is not detected
C:\Users\Tekme\Documents\QtStuf\quick\QmlCpp\message.h:15: error: 'authorChanged' was not declared in this scope
emit authorChanged();
^
my code is
#ifndef MESSAGE_H
#define MESSAGE_H
#include <QObject>
class Message : public QObject
{
Q_OBJECT
Q_PROPERTY(QString author READ author WRITE setAuthor NOTIFY authorChanged)
public:
void setAuthor(const QString &a) {
if (a != m_author) {
m_author = a;
emit authorChanged();
}
}
QString author() const {
return m_author;
}
private:
QString m_author;
};
#endif
and in my main.cpp
#include "message.h"
#include <QApplication>
#include <QQmlEngine>
#include <QQmlContext>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QQmlEngine engine;
Message msg;
engine.rootContext()->setContextProperty("msg",&msg);
QQmlComponent component(&engine, QUrl::fromLocalFile("main.qml"));
component.create();
return a.exec();
}
You are not including QQmlComponent header in your main.cpp:
#include <QQmlComponent>
You are also trying to emit a signal that you haven't declared yet. You should declare it in your message.h like this:
signals:
void authorChanged();
Check this example.
I believe you need to add:
signals:
void authorChanged();
to your class like this:
class Message : public QObject
{
Q_OBJECT
Q_PROPERTY(QString author READ author WRITE setAuthor NOTIFY authorChanged)
public:
void setAuthor(const QString &a) {
if (a != m_author) {
m_author = a;
emit authorChanged();
}
}
QString author() const {
return m_author;
}
signals:
void authorChanged();
private:
QString m_author;
};
I derived a class from QTextEdit and use it as a "logbook". I equipped it with a slot to receive log-messages.
class CLogbook : public QTextEdit
{
Q_OBJECT;
public:
void log(QString msg) {append(msg)};
public slots:
void recvLogSignal(const QString message)
{
append("hallo");
std::cout << "signal received.\n";
log(message);
}
};
another class then emits a signal like this:
// in the header
signals:
void logMessage(const QString);
// in the implementation
emit logMessage("qt is cute");
std::cout << "if you can read this the logMessage was emitted\n";
and also i connect the signal to the slot
connect(tableeditor, SIGNAL(logMessage(const QString)), logbook, SLOT(recvLogSignal(const QString)));
However the message is never shown in the "logbook". What am i missing here?
SOLVED: The connect method was called after emitting the signal :-(
It is hard to see exactly what is wrong with your implementation without a full example. Sometimes signals or slots will fail if an object goes out of scope if it isn't initialized on the heap.
Another way that it could fail is if your QApplication hasn't reached the exec() call.
I haven't experimented with using const in signal and slot calls, and I haven't seen it in any examples before, so that could be causing the problem; but it seems to work fine in the example below.
Working Example With a Derived Class of QTextEdit
Here is a simple example I put together that does some basic logging with a push button and a line edit.
Here is the header:
#ifndef WIDGET_H
#define WIDGET_H
#include <QtGui/QWidget>
//#include <QTextEdit>
#include "clogbook.h"
#include <QLineEdit>
class Widget : public QWidget
{
Q_OBJECT
public:
Widget(QWidget *parent = 0);
~Widget() {}
public slots:
void on_pushButton();
void on_lineEditReturn();
private:
CLogBook * text_edit_log;
QLineEdit * line_edit;
};
#endif // WIDGET_H
Here is the source:
#include "widget.h"
#include <QBoxLayout>
#include <QPushButton>
#include <QTimer>
Widget::Widget(QWidget *parent)
: QWidget(parent)
{
QBoxLayout * box_layout = new QBoxLayout(QBoxLayout::TopToBottom);
text_edit_log = new CLogBook;
line_edit = new QLineEdit("Type Here and press Enter.");
QPushButton * push_button = new QPushButton("Click to Add To Log");
text_edit_log->setText("My Log Book");
box_layout->addWidget(text_edit_log);
box_layout->addWidget(line_edit);
box_layout->addWidget(push_button);
this->setLayout(box_layout);
QObject::connect(push_button, SIGNAL(clicked()), this, SLOT(on_pushButton()));
QObject::connect(line_edit, SIGNAL(returnPressed()), this, SLOT(on_lineEditReturn()));
}
void Widget::on_pushButton()
{
// text_edit_log->append("Push Button Logging Test");
text_edit_log->recvLogSignal("Push button test.");
}
void Widget::on_lineEditReturn()
{
// text_edit_log->append(line_edit->text());
text_edit_log->recvLogSignal(QString("LineEdit: ") + line_edit->text() );
line_edit->clear();
}
And here is the main:
#include <QtGui/QApplication>
#include "widget.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget w;
w.show();
return a.exec();
}
And here is the CLogBook class:
#ifndef CLOGBOOK_H
#define CLOGBOOK_H
#include <QTextEdit>
#include <iostream>
class CLogBook : public QTextEdit
{
Q_OBJECT
public:
explicit CLogBook(QWidget *parent = 0) : QTextEdit(parent) { }
void log (QString msg) { append(msg); }
public slots:
void recvLogSignal(const QString message)
{
append("hallo");
std::cout << "signal received.\n" << std::endl;
log(message);
}
};
#endif // CLOGBOOK_H