long mouse press event

[tonylin0826]

Hi, if there is any way i can detect a mouse long press event in qt. Because i want to keep drawing a different circle on the mainwindow while my mouse is down. thanks)

[wysota]

Intercept mousePressEvent and start a timer there. Intercept a mouseMoveEvent or mouseReleaseEvent (depending on what you want to do) and check the timer. If it exceeds a predefined threshold, you have a long press, otherwise you have a short press.

[tonylin0826]

thanks, but i need to have a long press that can press as long time as i want. can a timer do that?

[wysota]

The timer doesn't care. It just measures time. If I understand you right and you want to keep increasing the circle diameter as the user is keeping the button down, you can start a timer to some short interval like 25ms and each time it fires, increase the diameter a bit. When the button is released, stop the timer and draw the final circle.

[tonylin0826]

thanks, but i need to draw the circle while i am pressing the left button not release the button. Can you teach me how?

[wysota]

thanks, but i need to draw the circle while i am pressing the left button not release the button.

That's what I meant. You are drawing the circle while the button is pressed but when it is released, you need to make your item permanent.

Here is a simple example that uses QGraphicsView:

#include <QtGui>
 
class View : public QGraphicsView {
  Q_OBJECT
public:
  View() : QGraphicsView() {
    current = 0;
    radius = 0;
    t.setInterval(10);
    connect(&t, SIGNAL(timeout()), this, SLOT(incDiameter()));
  }
 
  void mousePressEvent(QMouseEvent *me) {
    current = new QGraphicsEllipseItem;
    radius = 5;
    QRect r;
    r.setWidth(2*radius);
    r.setHeight(2*radius);
    r.moveCenter(mapToScene(me->pos()).toPoint());
    current->setRect(r);
    scene()->addItem(current);
    t.start();
  }
  void mouseReleaseEvent(QMouseEvent *me) {
    t.stop();
    current = 0;
  }
private slots:
  void incDiameter() {
    QRect r;
    radius++;
    r.setWidth(2*radius);
    r.setHeight(2*radius);
    r.moveCenter(current->rect().center().toPoint());
    current->setRect(r);
  }  
private:
  QGraphicsEllipseItem *current;
  QTimer t;
  int radius;
};
 
#include "main.moc"
 
 
int main(int argc, char **argv) {
  QApplication app(argc, argv);
  View view;
  view.setScene(new QGraphicsScene(0,0,600,400));
  view.show();
  return app.exec();
}

#include <QtGui>

class View : public QGraphicsView {
  Q_OBJECT
public:
  View() : QGraphicsView() {
    current = 0;
    radius = 0;
    t.setInterval(10);
    connect(&t, SIGNAL(timeout()), this, SLOT(incDiameter()));
  }
  
  void mousePressEvent(QMouseEvent *me) {
    current = new QGraphicsEllipseItem;
    radius = 5;
    QRect r;
    r.setWidth(2*radius);
    r.setHeight(2*radius);
    r.moveCenter(mapToScene(me->pos()).toPoint());
    current->setRect(r);
    scene()->addItem(current);
    t.start();
  }
  void mouseReleaseEvent(QMouseEvent *me) {
    t.stop();
    current = 0;
  }
private slots:
  void incDiameter() {
    QRect r;
    radius++;
    r.setWidth(2*radius);
    r.setHeight(2*radius);
    r.moveCenter(current->rect().center().toPoint());
    current->setRect(r);
  }  
private:
  QGraphicsEllipseItem *current;
  QTimer t;
  int radius;
};

#include "main.moc"


int main(int argc, char **argv) {
  QApplication app(argc, argv);
  View view;
  view.setScene(new QGraphicsScene(0,0,600,400));
  view.show();
  return app.exec();
}

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