QScrollarea events transferring to scrollbar

hi
i have subclassed QScrollArea to receive mouse move events .
now when i move the mouse the scrollbars should be moved accordingly(up and down movements for vertical scrollbar and left and right movements for horizontal scrollbar).

how can i transfer the mouse move event of scrollarea to scrollbar

Quote:

---

Originally Posted by babu198649

i have subclassed QScrollArea to receive mouse move events .
now when i move the mouse the scrollbars should be moved accordingly(up and down movements for vertical scrollbar and left and right movements for horizontal scrollbar).

how can i transfer the mouse move event of scrollarea to scrollbar

---

Why not use QScrollBar::setValue() to set the value of the scrollbar?

yes i have tried it but it makes exection slower.

i have tried like this

Code:

---

void iv_scrollarea::mouseMoveEvent ( QMouseEvent * event )
{
	if(this->underMouse())
	{
	if(old_position.x() > event->pos().x())//old position is qpoint it remembers last position
	  this->horizontalScrollBar()->setValue(this->horizontalScrollBar()->value() + 1);
 
	if(old_position.x() < event->pos().x())
	  this->horizontalScrollBar()->setValue(this->horizontalScrollBar()->value() - 1);
 
	if(old_position.y() > event->pos().y())
	  this->verticalScrollBar()->setValue(this->verticalScrollBar()->value() + 1);
 
	if(old_position.y() < event->pos().y())
	  this->verticalScrollBar()->setValue(this->verticalScrollBar()->value() - 1);
	}
       old_position = event->pos();
}

---

the above code takes long movement of the mouse to move the label inside the QScrollArea. because at every pixel moved the movement of label does not happen

and when i set values with higher than setValue(1) (i.e. this->verticalScrollBar()->setValue(this->verticalScrollBar()->value() - 5))

the flickering occurs:confused:


when i use the move() function of label inside scrollarea mouse move event it works fine but scrollbars are not updated

Ok, what effect are you trying to achieve anyway? Why do you add "1" instead of computing the actual movement?

Quote:

---

Ok, what effect are you trying to achieve anyway?

---

i want to move the qlabel inside the qscrollarea using mouse cursor (i.e. click and move the label) simultaneously the scrollbars should get updated.

Doesn't something like this work?

Code:

---

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
 
class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    QLabel *l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
  }
};
 
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

---

The scrolling works for me out of the box.

the problem is not with scrolling
when i move the qlabel with the mouse(clicked and move ) the label moves a distance with respect to the distance moved by the mouse .now the scrollbar should update this movement of the label.

Quote:

---

QLabel *l = new QLabel(this);
setWidget(l);

---

is this keyword nessary

Why don't you use built-in components, QMdiArea or QGraphicsView (depending on your needs) as already suggested in another thread?

hi
i have found in the documentation that the QGraphicsView is for maintaining large number of items . but i have only one label so i thought it will not suit.

and QMdiArea class documentation says

The QMdiArea widget provides an area in which MDI windows are displayed.

but i dont have more than one window and also i need time to know what MDI windows are . so i thought that i can do these things with qscrollarea itself.

do u think the problem can not be solved with QScrollarea

You should really use QMdiArea or QGraphicsView as suggested, but if you insist on using the scroll area directly then this works for me:

Code:

---

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>
 
 
class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
  }
  bool eventFilter(QObject *o, QEvent *e){
    if(o!=l)
      return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress){
      m_prev = ((QMouseEvent*)e)->pos();
      return true;
    }
    if(e->type()==QEvent::MouseMove){
      QPoint pt = ((QMouseEvent*)e)->pos();
      QPoint diff = pt-m_prev;
      m_prev = pt;
      horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x());
      verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y());
      return true;
    }
    return QScrollArea::eventFilter(o,e);
  }
protected:
  QLabel *l;
  QPoint m_prev;
};
 
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

---

Thank u very much wysota
it really works great .
thanks for pain taking job of coding entirely :o in a short perid for me

You would have saved me the pain if you used the right component for the job in the first place.

yes
but i followed the image viewer example

I advise you to follow JPN's hints next time. Your use case seemed a perfect candidate for QGraphicsView, especially if you intend to do something more with it (like introduce zooming).

sure, thank u

Quote:

---

Originally Posted by wysota

You should really use QMdiArea or QGraphicsView as suggested, but if you insist on using the scroll area directly then this works for me:

Code:

---

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>
 
 
class ScrollArea : public QScrollArea {
public:
  ScrollArea(const QString &path) : QScrollArea(0){
    l = new QLabel(this);
    setWidget(l);
    setWidgetResizable(true);
    l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
  }
  bool eventFilter(QObject *o, QEvent *e){
    if(o!=l)
      return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress){
      m_prev = ((QMouseEvent*)e)->pos();
      return true;
    }
    if(e->type()==QEvent::MouseMove){
      QPoint pt = ((QMouseEvent*)e)->pos();
      QPoint diff = pt-m_prev;
      m_prev = pt;
      horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x());
      verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y());
      return true;
    }
    return QScrollArea::eventFilter(o,e);
  }
protected:
  QLabel *l;
  QPoint m_prev;
};
 
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  ScrollArea sa(argv[1]);
  sa.show();
  return app.exec();
}

---

---

It makes something wrong when you drag it more than one pixel in one direction. Is accumulative. I got one solution for it:

Code:

---

#include <QScrollArea>
#include <QLabel>
#include <QApplication>
#include <QMouseEvent>
#include <QScrollBar>
#include<QDebug>
 
class ScrollArea : public QScrollArea {
public:
ScrollArea() : QScrollArea()
{
    this->n=3;
    this->prev_diff.setX(0);
    this->prev_diff.setY(0);
    l = new QLabel(this);
    QImage imagen("C:/donostia.jpg");
    l->setPixmap(QPixmap::fromImage(imagen));
    setWidget(l);
    setWidgetResizable(true);
    //l->setPixmap(QPixmap(path));
    l->installEventFilter(this);
}
bool eventFilter(QObject *o, QEvent *e)
{
    if(o!=l)
        return QScrollArea::eventFilter(o,e);
    if(e->type()==QEvent::MouseButtonPress)
    {
        m_prev = ((QMouseEvent*)e)->pos();
        this->prev_diff.setX(0);
        this->prev_diff.setY(0);
        return true;
    }
    if(e->type()==QEvent::MouseMove)
    {
        QPoint pt = ((QMouseEvent*)e)->pos();
        this->diff = pt-m_prev-prev_diff*n;
        m_prev = pt;
        horizontalScrollBar()->setValue(horizontalScrollBar()->value()+diff.x()*n);
        verticalScrollBar()->setValue(verticalScrollBar()->value()+diff.y()*n);
        qDebug()<<"("+QString::number(diff.x())+","+QString::number(diff.y())+")";
        this->prev_diff=diff;
        return true;
    }
    return QScrollArea::eventFilter(o,e);
}
protected:
    QLabel *l;
    QPoint m_prev;
    QPoint diff;
    QPoint prev_diff;
    int n;
};
 
 
int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    ScrollArea sa;
    sa.show();
    return app.exec();
}

---