QRubberBand

[A Former User]

I wrote this code to paint a rectangle when I press and move the mouse but it doesn't work...I don't understand why..can you help me?

void Widget::mousePressEvent(QMouseEvent *event)
{
origin = event->pos();
if (!rubberBand)
rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
rubberBand->setGeometry(QRect(origin, QSize()));
rubberBand->show();
}

void Widget::mouseMoveEvent(QMouseEvent *event)
{
rubberBand->setGeometry(QRect(origin, event->pos()).normalized());
}

void Widget::mouseReleaseEvent(QMouseEvent *event)
{
rubberBand->hide();
// determine selection, for example using QRect::intersects()
// and QRect::contains().
}

[A Former User]

@SGaist thanks

[raven-worx]

@vale88 said in QRubberBand:

but it doesn't work

what happens instead?
Are you sure the mouseMoveEvent() event handler is called?

[A Former User]

@raven-worx nothing happends ..I don't understand..I move the mouse but nothing happends

[SGaist]

Hi,

That might sound silly but are you first pressing one of the mouse button ?

To ensure that your methods are called you can put qDebug statements in each of them.

[A Former User]

@SGaist event are void function...yes,I pres the button of the mouse

[SGaist]

@vale88 said in QRubberBand:

@SGaist event are void function...yes,I pres the button of the mouse

What do you mean by event are void function ? And were is it related to my suggestion of putting qDebug statements in these functions to check what is happening ?

[A Former User]

Events work with qDebug().
But when insert code of rectangular, it doesn't work.
There is a crash in the application.

[A Former User]

Thisi is my code .cpp :

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QRubberBand>
#include <QMouseEvent>

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}

MainWindow::~MainWindow()
{
delete ui;
}

void MainWindow::mousePressEvent(QMouseEvent * event)

{

origin = event->pos();
   if (!rubberBand)
       rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
   rubberBand->setGeometry(QRect(origin, QSize(20,10)));
   rubberBand->show();

ui->textBrowser->append("press");

}

void MainWindow::mouseReleaseEvent(QMouseEvent *event)
{
rubberBand->setGeometry(QRect(origin, event->pos()).normalized());
ui->textBrowser->append("release");
}

void MainWindow::mouseMoveEvent(QMouseEvent *event)
{
rubberBand->hide();
ui->textBrowser->append("move");
}

And .h :

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QRubberBand>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = nullptr);
~MainWindow();
void mousePressEvent(QMouseEvent * event);
void mouseMoveEvent(QMouseEvent * event);
void mouseReleaseEvent(QMouseEvent * event);

private:
Ui::MainWindow *ui;
QPoint origin;
QRubberBand *rubberBand;
};

#endif // MAINWINDOW_H

I don't know if something there isn't.

[SGaist]

You forgot to initialise your QRubberBand variable to nullptr in the constructor.

[A Former User]

@SGaist thanks