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
:confused:

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


--------------------------------------------
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");
}

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

[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
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 ) 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



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);
}


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

[jpn]

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


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
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;
...
...
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


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_*/

MyLabel.cpp

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


}


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

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();

}
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();
}


Thank you for your interest.