C++ Using QT Creator

[faieq92]

Hello I seem to keep getting random error messages when trying to compile and run my program.

mainwindow.obj:-1: error: LNK2019: unresolved external symbol "public: __thiscall mycell::mycell(void)" (??0mycell@@QAE@XZ) referenced in function "public: __thiscall MainWindow::MainWindow(class QWidget *)" (??0MainWindow@@QAE@PAVQWidget@@@Z)

debug\18.exe:-1: error: LNK1120: 1 unresolved externals

this is the error im currently getting.

could anyone be kind enough as to explain what this means.

[faieq92]

if it helps here is all my code including header files

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QtGui>
#include <QtCore>
#include "mycell.h"

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
    
private:
    Ui::MainWindow *ui;
    QGraphicsScene *scene;
    mycell *square;

};

#endif // MAINWINDOW_H 

#ifndef MYCELL_H
#define MYCELL_H
#include <QPainter>
#include <QGraphicsItem>
#include "mainwindow.h"


class mycell : public QGraphicsItem

{
public:
    mycell();
    // outer edges of the object
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
    bool Pressed;

protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event);
    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
};

#endif // MYCELL_H 

#ifndef MYCELL_H
#define MYCELL_H
#include <QPainter>
#include <QGraphicsItem>
#include "mainwindow.h"


class mycell : public QGraphicsItem

{
public:
    mycell();
    // outer edges of the object
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
    bool Pressed;

protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event);
    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
};

#endif // MYCELL_H 

#include "mycell.h"
#include "mainwindow.h"

mycell::mycell()
{
    Pressed = false;
    setFlag(ItemIsMovable);
}

QRectF mycell::boundingRect() const
{
    return QRectF(0,0,100,100);
}

void mycell::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QRectF rec = boundingRect();
    QBrush brush(Qt::blue);


    if (Pressed){
        brush.setColor(Qt::red) ;
    }
    else{
        brush.setColor(Qt::blue) ;
    }
    painter->fillRect(rec,brush);
    painter->drawRect(rec);
}


void mycell::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    Pressed = true;
    update();
    QGraphicsItem::mousePressEvent(event);
}

void mycell::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
    Pressed = false;
    update();
    QGraphicsItem::mousePressEvent(event);
}

[faieq92]

it has something to do with me putting the class my cell into the mainwindow.h file

as it goes when I remove it from there but I don't understand why I cant put it in there?

[faieq92]

anyone?

[coder777]

it has something to do with me putting the class my cell into the mainwindow.h file

No, it's a pointer anyway, so there shouldn't be a problem.

Did you add the 'mycell.cpp' or however you named properly to your project

[Nobun]

usually, when you use single-inheritance approach for widgets created with Qt designer you would use Ui::MainWindow ui and NOT Ui::MainWindow * ui.

typical usage

MainWindow::MainWindow(QWidget * parent) : QMainWindow(parent) {
  ui.setupUi(this);
}

PS: I never used "explicit" for a constructor.... I don't see any reason mainly for a QObject derived class (I remember that widgets are subclass of QObject... QObject subclasses are treated in a very special way so I am not sure it is a good idea to declare an explicit constructor).

----

I don't know if those hints can help you

[faieq92]

still haven't managed to get rid of the error if anyone can help

[faieq92]

the problem comes up when I call this

    item = new MyCell();
    scene->addItem(item);

[faieq92]

anyone?

[Nobun]

I suggest you to DON'T use directly QGraphicItem but to use one of the conveniences available

here is the list, ripped from QGraphicItem documentation page:

QGraphicsEllipseItem provides an ellipse item
QGraphicsLineItem provides a line item
QGraphicsPathItem provides an arbitrary path item
QGraphicsPixmapItem provides a pixmap item
QGraphicsPolygonItem provides a polygon item
QGraphicsRectItem provides a rectangular item
QGraphicsSimpleTextItem provides a simple text label item
QGraphicsTextItem provides an advanced text browser item

For example, in one of my program, I create a class derived from QGraphicPixmapItem to extend some functionalities I specific need for my program (like the chance to change easly the coords where to put my item and chance to change the image associated with it)

[Stewbond]

Make sure you have mycell.cpp added to your .pro file under the SOURCES: section.

#-------------------------------------------------
#
# Project created by QtCreator 2013-04-05T20:38:52
#
#-------------------------------------------------

QT       += core gui

TARGET = Qtest
TEMPLATE = app

SOURCES += main.cpp\
           mainwindow.cpp \
           mycell.cpp

HEADERS += mainwindow.h \
           mycell.h

FORMS   += mainwindow.ui \
           mycell.ui

If you've done this, what text is in your .pro file?

[faieq92]

#-------------------------------------------------
#
# Project created by QtCreator 2013-04-20T20:36:36
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = Game
TEMPLATE = app


SOURCES += main.cpp\
        dialog.cpp \
    mycell.cpp

HEADERS  += dialog.h \
    mycell.h

FORMS    += dialog.ui

[faieq92]

that's the pro file

[faieq92]

im still getting the error