Draw Line :confused:

[sabeesh]

Hi,
I am new in QT. I do some small programes in QT.4.2.2. Now I try to
create a small program, which one draw a line in a particular widget
( label ). I create a form in QT4.2.2 and place three labels in that form named as Label1,
Label2 and Label3 and a pushButton.I need to run the program like this,
when i click on the pushbutton, then a line draw in a label3. How can i
do this?. I create two file like this, Please help me,
Sabeesh C.S


testdraw.h
************************

#ifndef MYQTAPP_H
#define MYQTAPP_H
#include <QWidget>
#include "ui_testdraw.h"
 
class myQtApp : public QMainWindow, private Ui::MainWindow
{
Q_OBJECT
public:
myQtApp(QWidget *parent = 0);
public slots:
void draw();
protected:
};
#endif

#ifndef MYQTAPP_H
#define MYQTAPP_H
#include <QWidget>
#include "ui_testdraw.h"

class myQtApp : public QMainWindow, private Ui::MainWindow
{
Q_OBJECT
public:
myQtApp(QWidget *parent = 0);
public slots:
void draw();
protected:
};
#endif

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--------------------------------------------
testdraw.cpp
*************************

#include <QtGui>
#include <qpainter.h>
#include "testdraw.h"
myQtApp::myQtApp(QWidget *parent)
{
setupUi(this);
connect( pushButton, SIGNAL( clicked() ), this, SLOT( draw() ) );
}
 
 
void QLabel::paintEvent( QPaintEvent * ) {
QPainter painter( this );
painter.setPen(Qt::blue);
painter.setFont(QFont("Arial", 40));
QLineF line(10.0, 10.0, 10.0, 120.0);
painter.drawLine(line);
}
 
 
void myQtApp::draw() {
qDebug("Hello");
}

#include <QtGui>
#include <qpainter.h>
#include "testdraw.h"
myQtApp::myQtApp(QWidget *parent)
{
setupUi(this);
connect( pushButton, SIGNAL( clicked() ), this, SLOT( draw() ) );
}


void QLabel::paintEvent( QPaintEvent * ) {
QPainter painter( this );
painter.setPen(Qt::blue);
painter.setFont(QFont("Arial", 40));
QLineF line(10.0, 10.0, 10.0, 120.0);
painter.drawLine(line);
}


void myQtApp::draw() {
qDebug("Hello");
}

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------------------------------------

[jacek]

If you want to draw on a label, you have to create a subclass and use that subclass instead.

[anafor2004]

How can we do this subclassing? Can you give me an instance and example?

[ashukla]

How can we do this subclassing? Can you give me an instance and example?

#ifndef MYLABEL_H
#define MYLABEL_H
#include <QLabel>
 
class MyLabel : public QLabel
{
    Q_OBJECT
 
public:
    MyLabel(QWidget *parent = 0);
 
 
};
#endif

#ifndef MYLABEL_H
#define MYLABEL_H
#include <QLabel>

class MyLabel : public QLabel
{
    Q_OBJECT
    
public:
    MyLabel(QWidget *parent = 0);
    
    
};
#endif

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This is a prototype for your QLabel. Then you reimplement & add some functions according to your need.

[anafor2004]

Thanks for your reply but i wonder that how can we connect this paint event with my label on my form ,

Do I have to use this?

class drawLabel : public QLabel,public Ui::Label

[ashukla]

Thanks for your reply but i wonder that how can we connect this paint event with my label on my form ,

Do I have to use this?

class drawLabel : public QLabel,public Ui::Label

No, Because It cause a problem of inheriting two QObject. you can put

virtual void paintEvent ( QPaintEvent * event )

virtual void paintEvent ( QPaintEvent * event )

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in your MyLabel class definition and then reimplement It in corresponding .cpp file.

[anafor2004]

This is what I did, but it didnt work.Why? Can you check it ?

cizim.h

#ifndef CIZIM_H
#define CIZIM_H
 
#include <QtGui/QMainWindow>
#include <QPainter>
#include "ui_cizim.h"
 
class cizim : public QMainWindow
{
    Q_OBJECT
 
public:
    cizim(QWidget *parent = 0);
    ~cizim();
 
private:
    Ui::cizimClass ui;
 
protected:
 
 
public slots:
	void draw();
 
};
 
#endif // CIZIM_H

#ifndef CIZIM_H
#define CIZIM_H

#include <QtGui/QMainWindow>
#include <QPainter>
#include "ui_cizim.h"

class cizim : public QMainWindow
{
    Q_OBJECT

public:
    cizim(QWidget *parent = 0);
    ~cizim();

private:
    Ui::cizimClass ui;
   
protected:
	
	
public slots:
	void draw();

};

#endif // CIZIM_H

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cizim.cpp

#include "cizim.h"
 
cizim::cizim(QWidget *parent)
    : QMainWindow(parent)
{
	ui.setupUi(this);
	QObject::connect( ui.pushButton, SIGNAL( clicked() ), ui.label, SLOT( draw() ) );
 
 
}
 
cizim::~cizim()
{
 
}
 
void cizim::draw()
{
	 QPainter painter(ui.label);
	 painter.setPen(Qt::blue);
	 painter.drawLine(0,0,200,200);
}

#include "cizim.h"

cizim::cizim(QWidget *parent)
    : QMainWindow(parent)
{
	ui.setupUi(this);
	QObject::connect( ui.pushButton, SIGNAL( clicked() ), ui.label, SLOT( draw() ) );
	
	
}

cizim::~cizim()
{

}

void cizim::draw()
{
	 QPainter painter(ui.label);
	 painter.setPen(Qt::blue);
	 painter.drawLine(0,0,200,200);
}

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ui_cizim.h

/********************************************************************************
** Form generated from reading ui file 'cizim.ui'
**
** Created: Thu 24. Jan 11:34:02 2008
**      by: Qt User Interface Compiler version 4.3.3
**
** WARNING! All changes made in this file will be lost when recompiling ui file!
********************************************************************************/
 
#ifndef UI_CIZIM_H
#define UI_CIZIM_H
 
#include <QtCore/QVariant>
#include <QtGui/QAction>
#include <QtGui/QApplication>
#include <QtGui/QButtonGroup>
#include <QtGui/QLabel>
#include <QtGui/QMainWindow>
#include <QtGui/QMenuBar>
#include <QtGui/QPushButton>
#include <QtGui/QStatusBar>
#include <QtGui/QWidget>
 
class Ui_cizimClass
{
public:
    QWidget *centralwidget;
    QPushButton *pushButton;
    QLabel *label;
    QMenuBar *menubar;
    QStatusBar *statusbar;
 
    void setupUi(QMainWindow *cizimClass)
    {
    if (cizimClass->objectName().isEmpty())
        cizimClass->setObjectName(QString::fromUtf8("cizimClass"));
    cizimClass->resize(800, 600);
    centralwidget = new QWidget(cizimClass);
    centralwidget->setObjectName(QString::fromUtf8("centralwidget"));
    pushButton = new QPushButton(centralwidget);
    pushButton->setObjectName(QString::fromUtf8("pushButton"));
    pushButton->setGeometry(QRect(90, 180, 121, 71));
    label = new QLabel(centralwidget);
    label->setObjectName(QString::fromUtf8("label"));
    label->setGeometry(QRect(270, 70, 351, 331));
    cizimClass->setCentralWidget(centralwidget);
    menubar = new QMenuBar(cizimClass);
    menubar->setObjectName(QString::fromUtf8("menubar"));
    menubar->setGeometry(QRect(0, 0, 800, 19));
    cizimClass->setMenuBar(menubar);
    statusbar = new QStatusBar(cizimClass);
    statusbar->setObjectName(QString::fromUtf8("statusbar"));
    cizimClass->setStatusBar(statusbar);
 
    retranslateUi(cizimClass);
 
    QMetaObject::connectSlotsByName(cizimClass);
    } // setupUi
 
    void retranslateUi(QMainWindow *cizimClass)
    {
    cizimClass->setWindowTitle(QApplication::translate("cizimClass", "MainWindow", 0, QApplication::UnicodeUTF8));
    pushButton->setText(QApplication::translate("cizimClass", "PushButton", 0, QApplication::UnicodeUTF8));
    label->setText(QString());
    Q_UNUSED(cizimClass);
    } // retranslateUi
 
};
 
namespace Ui {
    class cizimClass: public Ui_cizimClass {};
} // namespace Ui
 
#endif // UI_CIZIM_H

/********************************************************************************
** Form generated from reading ui file 'cizim.ui'
**
** Created: Thu 24. Jan 11:34:02 2008
**      by: Qt User Interface Compiler version 4.3.3
**
** WARNING! All changes made in this file will be lost when recompiling ui file!
********************************************************************************/

#ifndef UI_CIZIM_H
#define UI_CIZIM_H

#include <QtCore/QVariant>
#include <QtGui/QAction>
#include <QtGui/QApplication>
#include <QtGui/QButtonGroup>
#include <QtGui/QLabel>
#include <QtGui/QMainWindow>
#include <QtGui/QMenuBar>
#include <QtGui/QPushButton>
#include <QtGui/QStatusBar>
#include <QtGui/QWidget>

class Ui_cizimClass
{
public:
    QWidget *centralwidget;
    QPushButton *pushButton;
    QLabel *label;
    QMenuBar *menubar;
    QStatusBar *statusbar;

    void setupUi(QMainWindow *cizimClass)
    {
    if (cizimClass->objectName().isEmpty())
        cizimClass->setObjectName(QString::fromUtf8("cizimClass"));
    cizimClass->resize(800, 600);
    centralwidget = new QWidget(cizimClass);
    centralwidget->setObjectName(QString::fromUtf8("centralwidget"));
    pushButton = new QPushButton(centralwidget);
    pushButton->setObjectName(QString::fromUtf8("pushButton"));
    pushButton->setGeometry(QRect(90, 180, 121, 71));
    label = new QLabel(centralwidget);
    label->setObjectName(QString::fromUtf8("label"));
    label->setGeometry(QRect(270, 70, 351, 331));
    cizimClass->setCentralWidget(centralwidget);
    menubar = new QMenuBar(cizimClass);
    menubar->setObjectName(QString::fromUtf8("menubar"));
    menubar->setGeometry(QRect(0, 0, 800, 19));
    cizimClass->setMenuBar(menubar);
    statusbar = new QStatusBar(cizimClass);
    statusbar->setObjectName(QString::fromUtf8("statusbar"));
    cizimClass->setStatusBar(statusbar);

    retranslateUi(cizimClass);

    QMetaObject::connectSlotsByName(cizimClass);
    } // setupUi

    void retranslateUi(QMainWindow *cizimClass)
    {
    cizimClass->setWindowTitle(QApplication::translate("cizimClass", "MainWindow", 0, QApplication::UnicodeUTF8));
    pushButton->setText(QApplication::translate("cizimClass", "PushButton", 0, QApplication::UnicodeUTF8));
    label->setText(QString());
    Q_UNUSED(cizimClass);
    } // retranslateUi

};

namespace Ui {
    class cizimClass: public Ui_cizimClass {};
} // namespace Ui

#endif // UI_CIZIM_H

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[jpn]

void cizim::draw()
{
	 QPainter painter(ui.label);
	 painter.setPen(Qt::blue);
	 painter.drawLine(0,0,200,200);
}

void cizim::draw()
{
	 QPainter painter(ui.label);
	 painter.setPen(Qt::blue);
	 painter.drawLine(0,0,200,200);
}

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You can't paint on widgets like this in Qt 4. Every widget paints itself in paintEvent(). No widget can paint on other widget and all painting happens during paintEvent().

[ashukla]

First you implement the class like this;
//mylabel.h

#ifndef MYLABEL_H
#define MYLABEL_H
#include <QLabel>
class MyLabel : public QLabel
{
Q_OBJECT
public:
    MyLabel(QWidget *parent = 0);
    virtual void paintEvent ( QPaintEvent * event );
};
#endif

#ifndef MYLABEL_H
#define MYLABEL_H
#include <QLabel>
class MyLabel : public QLabel
{
Q_OBJECT
public:
    MyLabel(QWidget *parent = 0);
    virtual void paintEvent ( QPaintEvent * event );
};
#endif

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and then write its corresponding mylabel.cpp. and its paintEvent you draw the line. After that you can use this label class in your constructor after setupUi(this). or use

#include "mylabel.h"
class Ui_cizimClass
{
public:
....
....
MyLabel *label;//QLabel *label;
...
...

#include "mylabel.h"
class Ui_cizimClass
{
public:
....
....
MyLabel *label;//QLabel *label;
...
...

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You can attach code by the attachments tool.

[anafor2004]

Hi I tried to do this but i think , still make some mistake can you check please. Sorry for that I am a new beginner!!!

ui_cizim.h (I changed QLabel as MyLabel)

#include <QtGui/QButtonGroup>
#include "MyLabel.h"
#include <QtGui/QMainWindow>
#include <QtGui/QPushButton>
#include <QtGui/QStatusBar>
#include <QtGui/QWidget>
 
class Ui_cizimClass
{
public:
    QWidget *centralwidget;
    QPushButton *pushButton;
    MyLabel *label;
    QStatusBar *statusbar;
 
    void setupUi(QMainWindow *cizimClass)
    {
    if (cizimClass->objectName().isEmpty())
        cizimClass->setObjectName(QString::fromUtf8("cizimClass"));
    cizimClass->resize(800, 600);
    centralwidget = new QWidget(cizimClass);
    centralwidget->setObjectName(QString::fromUtf8("centralwidget"));
    pushButton = new QPushButton(centralwidget);
    pushButton->setObjectName(QString::fromUtf8("pushButton"));
    pushButton->setGeometry(QRect(90, 180, 121, 71));
    label = new MyLabel(centralwidget);
    label->setObjectName(QString::fromUtf8("label"));
    label->setGeometry(QRect(270, 70, 401, 331));
    cizimClass->setCentralWidget(centralwidget);
    statusbar = new QStatusBar(cizimClass);
    statusbar->setObjectName(QString::fromUtf8("statusbar"));
    cizimClass->setStatusBar(statusbar);
 
    retranslateUi(cizimClass);
 
    QMetaObject::connectSlotsByName(cizimClass);
    } // setupUi
 
    void retranslateUi(QMainWindow *cizimClass)
    {
    cizimClass->setWindowTitle(QApplication::translate("cizimClass", "MainWindow", 0, QApplication::UnicodeUTF8));
    pushButton->setText(QApplication::translate("cizimClass", "PushButton", 0, QApplication::UnicodeUTF8));
    label->setText(QString());
    Q_UNUSED(cizimClass);
    } // retranslateUi
 
};
 
namespace Ui {
    class cizimClass: public Ui_cizimClass {};
} // namespace Ui
 
#endif // UI_CIZIM_H

#include <QtGui/QButtonGroup>
#include "MyLabel.h"
#include <QtGui/QMainWindow>
#include <QtGui/QPushButton>
#include <QtGui/QStatusBar>
#include <QtGui/QWidget>

class Ui_cizimClass
{
public:
    QWidget *centralwidget;
    QPushButton *pushButton;
    MyLabel *label;
    QStatusBar *statusbar;

    void setupUi(QMainWindow *cizimClass)
    {
    if (cizimClass->objectName().isEmpty())
        cizimClass->setObjectName(QString::fromUtf8("cizimClass"));
    cizimClass->resize(800, 600);
    centralwidget = new QWidget(cizimClass);
    centralwidget->setObjectName(QString::fromUtf8("centralwidget"));
    pushButton = new QPushButton(centralwidget);
    pushButton->setObjectName(QString::fromUtf8("pushButton"));
    pushButton->setGeometry(QRect(90, 180, 121, 71));
    label = new MyLabel(centralwidget);
    label->setObjectName(QString::fromUtf8("label"));
    label->setGeometry(QRect(270, 70, 401, 331));
    cizimClass->setCentralWidget(centralwidget);
    statusbar = new QStatusBar(cizimClass);
    statusbar->setObjectName(QString::fromUtf8("statusbar"));
    cizimClass->setStatusBar(statusbar);

    retranslateUi(cizimClass);

    QMetaObject::connectSlotsByName(cizimClass);
    } // setupUi

    void retranslateUi(QMainWindow *cizimClass)
    {
    cizimClass->setWindowTitle(QApplication::translate("cizimClass", "MainWindow", 0, QApplication::UnicodeUTF8));
    pushButton->setText(QApplication::translate("cizimClass", "PushButton", 0, QApplication::UnicodeUTF8));
    label->setText(QString());
    Q_UNUSED(cizimClass);
    } // retranslateUi

};

namespace Ui {
    class cizimClass: public Ui_cizimClass {};
} // namespace Ui

#endif // UI_CIZIM_H

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MyLabel.h

#ifndef MYLABEL_H
#define MYLABEL_H
#include <QLabel>
#include<QPainter>
 
class MyLabel : public QLabel
{
Q_OBJECT
public:
    MyLabel(QWidget *);
    virtual void paintEvent ( QPaintEvent * event )
    {
    	QPainter painter(this);
    	painter.setPen(Qt::blue);
    	painter.drawLine(0,0,100,100);
 
 
 
    }
};
#endif /*SON_H_*/

#ifndef MYLABEL_H
#define MYLABEL_H
#include <QLabel>
#include<QPainter>

class MyLabel : public QLabel
{
Q_OBJECT
public:
    MyLabel(QWidget *);
    virtual void paintEvent ( QPaintEvent * event )
    {
    	QPainter painter(this);
    	painter.setPen(Qt::blue);
    	painter.drawLine(0,0,100,100);

    	
    	
    }
};
#endif /*SON_H_*/

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MyLabel.cpp

#include "MyLabel.h"
MyLabel::MyLabel(QWidget *)
{
 
 
}

#include "MyLabel.h"
MyLabel::MyLabel(QWidget *)
{
	

}

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Cizim.h

#ifndef CIZIM_H
#define CIZIM_H
 
#include <QtGui/QMainWindow>
#include <QPainter>
#include "ui_cizim.h"
//#include "son.h"
class cizim : public QMainWindow,public QLabel
{
    Q_OBJECT
 
public:
    cizim(QWidget *parent = 0);
    ~cizim();
 
private:
    Ui::cizimClass ui;
 
protected:
 
 
public slots:
	void draw();
 
};
 
#endif // CIZIM_H

#ifndef CIZIM_H
#define CIZIM_H

#include <QtGui/QMainWindow>
#include <QPainter>
#include "ui_cizim.h"
//#include "son.h"
class cizim : public QMainWindow,public QLabel
{
    Q_OBJECT

public:
    cizim(QWidget *parent = 0);
    ~cizim();

private:
    Ui::cizimClass ui;
   
protected:
	
	
public slots:
	void draw();

};

#endif // CIZIM_H

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Cizim.cpp

#include "cizim.h"
cizim::cizim(QWidget *parent)
    : QMainWindow(parent)
{
	ui.setupUi(this);
	connect( ui.pushButton, SIGNAL( clicked() ),this,SLOT( draw() ) );
}
 
cizim::~cizim()
{
 
}
 
void cizim::draw()
{
 
	ui.label->repaint();
	//this->close();
 
}

#include "cizim.h"
cizim::cizim(QWidget *parent)
    : QMainWindow(parent)
{
	ui.setupUi(this);
	connect( ui.pushButton, SIGNAL( clicked() ),this,SLOT( draw() ) );
}

cizim::~cizim()
{

}

void cizim::draw()
{
	
	ui.label->repaint();
	//this->close();
	
}

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main.cpp

#include "cizim.h"
#include "MyLabel.h"
#include <QtGui>
#include <QApplication>
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    cizim w;
    w.show();
    a.connect(&a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()));
    return a.exec();
}

#include "cizim.h"
#include "MyLabel.h"
#include <QtGui>
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    cizim w;
    w.show();
    a.connect(&a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()));
    return a.exec();
}

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Thank you for your interest.