Graphics View mouse events

[wlmirand]

Hi, im new with Qt and id like to learn a few simple things about event handling in QGraphicsView.

For now, id like to draw rects and be able to pop a messagebox with some info about clicked rect (position, size).

To achieve this, i put a QGraphicsView widget in my window and wrote a function that generate a random QRect and call myScene->addRect(myRect) to populate my scene.

Finally I use myScene->show();

Until here, is everything fine.

The problem is to write mouse event function. Ive googled a lot and read Graphics View Framework documentation too and i still dont understand how events get propagated from QGraphicsView, to QGraphicsScene, and then to QGraphicsItem

As I seen on "Diagram Scene" example, Ive create a class that "extends" QGraphicsScene and I reimplemented "void mousePressEvent(...)", but it didnt worked.

My question is: Which classes I must inherit, to override mouse events, and where should i handle them.

Thanks in advance

[helloworld]

Ive create a class that "extends" QGraphicsScene and I reimplemented "void mousePressEvent(...)", but it didnt worked.

In what way doesn't it work? It would also help if you provide the piece of code that contains your implementation of mousePressEvent.

[wlmirand]

Hi. The function mousePressEvent doesnt "run" when I click. Here is the code:

customscene.h

#ifndef CUSTOMSCENE_H
#define CUSTOMSCENE_H
 
#include <QGraphicsScene>
#include <QGraphicsSceneEvent>
 
class CustomScene : public QGraphicsScene
{
    Q_OBJECT
public:
    explicit CustomScene(QObject *parent = 0);
 
signals:
 
public slots:
 
protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent);
 
};
 
#endif // CUSTOMSCENE_H

#ifndef CUSTOMSCENE_H
#define CUSTOMSCENE_H

#include <QGraphicsScene>
#include <QGraphicsSceneEvent>

class CustomScene : public QGraphicsScene
{
    Q_OBJECT
public:
    explicit CustomScene(QObject *parent = 0);

signals:

public slots:

protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent);

};

#endif // CUSTOMSCENE_H

To copy to clipboard, switch view to plain text mode 

customscene.cpp

#include "customscene.h"
#include <QMessageBox>
 
CustomScene::CustomScene(QObject *parent) :
    QGraphicsScene(parent)
{
 
}
 
void CustomScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
    QMessageBox msg;
 
    msg.setText("clicked"); //a test to see if the function is called
    msg.exec();
}

#include "customscene.h"
#include <QMessageBox>

CustomScene::CustomScene(QObject *parent) :
    QGraphicsScene(parent)
{

}

void CustomScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
    QMessageBox msg;

    msg.setText("clicked"); //a test to see if the function is called
    msg.exec();
}

To copy to clipboard, switch view to plain text mode 

mainwindow.cpp

CustomScene *scene;
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    scene = new CustomScene;
    ui->GraphicsView->setScene(scene);
}
 
void MainWindow::on_button_clicked()
{
        scene->addRect(0,0,630,280);//draw a big rect
 
        QPen borda;
        borda.setStyle(Qt::DashDotLine);
        borda.setWidth(2);
        borda.setBrush(Qt::green);
        borda.setCapStyle(Qt::RoundCap);
        borda.setJoinStyle(Qt::RoundJoin);
 
        QBrush fundo;
        fundo.setStyle(Qt::SolidPattern);
        fundo.setColor(QColor(0,0,255,85));
 
        QRect rect(30,30,60,60); //draw a small rect inside
 
        scene->addRect(rect, borda, fundo);
 
        ui->GraphicsView->show();
}

CustomScene *scene;

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

    scene = new CustomScene;
    ui->GraphicsView->setScene(scene);
}

void MainWindow::on_button_clicked()
{
        scene->addRect(0,0,630,280);//draw a big rect

        QPen borda;
        borda.setStyle(Qt::DashDotLine);
        borda.setWidth(2);
        borda.setBrush(Qt::green);
        borda.setCapStyle(Qt::RoundCap);
        borda.setJoinStyle(Qt::RoundJoin);

        QBrush fundo;
        fundo.setStyle(Qt::SolidPattern);
        fundo.setColor(QColor(0,0,255,85));

        QRect rect(30,30,60,60); //draw a small rect inside

        scene->addRect(rect, borda, fundo);

        ui->GraphicsView->show();
}

To copy to clipboard, switch view to plain text mode 

It was supposed to pop the MessageBox when I click the GraphicsView, but nothing happens