How to draw QRubberBand on a QGraphicsView using Mouse? - c++

Question

I have my MainWindow with a GraphicsView on which I want to draw a QRubberBand using MouseEvents. Therefore I created a custom GraphicsView class where I have the MouseEvents, however since I am a beginner, I don't know how to connect everything to the MainWindow.
Here's what I got so far:
mousegraphics.h (custom)
#ifndef MOUSEGRAPHICS_H
#define MOUSEGRAPHICS_H
#include <QGraphicsView>
#include <QWidget>
#include <QMainWindow>
#include <QRubberBand>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QMouseEvent>
#include <QEvent>
class MouseGraphics : public QGraphicsView
{
public:
MouseGraphics(QWidget* parent = nullptr);
public slots:
void mousePressEvent(QMouseEvent* e);
void mouseMoveEvent(QMouseEvent* e);
void mouseReleaseEvent(QMouseEvent* e);
private:
QRubberBand* rb = nullptr;
// Coordinates
QPoint origin, dest;
};
#endif // MOUSEGRAPHICS_H
mousegraphics.cpp
#include "mousegraphics.h"
MouseGraphics::MouseGraphics(QWidget* parent) : QGraphicsView(parent)
{
}
void MouseGraphics::mousePressEvent(QMouseEvent *e)
{
origin = e->pos();
if(!rb)
{
rb = new QRubberBand(QRubberBand::Line, this);
}
rb->setGeometry(QRect(origin, QSize()));
rb->show();
}
void MouseGraphics::mouseMoveEvent(QMouseEvent *e)
{
rb->setGeometry(QRect(origin, e->pos()).normalized());
}
void MouseGraphics::mouseReleaseEvent(QMouseEvent *e)
{
rb->hide();
}
mainwindow.h:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QRubberBand>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QMouseEvent>
#include <QEvent>
#include "mousegraphics.h"
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
public slots:
void mousePressEvent(QMouseEvent *e);
void mouseMoveEvent(QMouseEvent *e);
void mouseReleaseEvent(QMouseEvent *e);
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

Answer 1

you should create one class that inherits from QGraphicsView.
because you need mousePressEvent ,mouseReleaseEvent , mouseMoveEvent of QGraphicsView.
Then in MainWindow, you need one QGraphicsScene object and I create one QGridLayout and with the addWidget function add my QGraphicsView object to MainWindow UI.
So I do this :
In graphicsview.h:
#ifndef GRAPHICSVIEW_H
#define GRAPHICSVIEW_H
#include <QGraphicsView>
#include <QObject>
#include <QRubberBand>
class graphicsView: public QGraphicsView
{
public:
graphicsView();
protected:
void mousePressEvent(QMouseEvent *event);
void mouseReleaseEvent(QMouseEvent *event);
void mouseMoveEvent(QMouseEvent *event);
private:
QRubberBand *rubberBand = nullptr;
QPoint origin;
};
#endif // GRAPHICSVIEW_H
graphicsview.cpp :
#include "graphicsview.h"
#include <QMouseEvent>
#include <QRect>
graphicsView::graphicsView()
{
}
void graphicsView::mousePressEvent(QMouseEvent *event)
{
origin = event->pos();
if (!rubberBand)
{
rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
}
rubberBand->setGeometry(QRect(origin, QSize()));
rubberBand->show();
}
void graphicsView::mouseReleaseEvent(QMouseEvent *event)
{
rubberBand->hide();
}
void graphicsView::mouseMoveEvent(QMouseEvent *event)
{
rubberBand->setGeometry(QRect(origin, event->pos()).normalized());
}
In mainwindow.h :
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
QT_BEGIN_NAMESPACE
namespace Ui
{
class MainWindow;
}
QT_END_NAMESPACE
class MainWindow: public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
In mainwindow.cpp :
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QGraphicsScene>
#include <QGridLayout>
#include "graphicsview.h"
MainWindow::MainWindow(QWidget *parent):
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
QGridLayout *gridLayout;
gridLayout = new QGridLayout(centralWidget());
gridLayout->setObjectName(QString::fromUtf8("gridLayout"));
auto scene = new QGraphicsScene(this);
graphicsView *_view = new graphicsView();
_view->setScene(scene);
gridLayout->addWidget(_view);
}
MainWindow::~MainWindow()
{
delete ui;
}
The result is this
: