[SOLVED] QT and C++ - Access Existing Widget from Event Handler

[BnMcG]

Hello all,

I'm trying to use QGraphicsView, QGraphicsScene and the mousePressed listener. The graphics view & scene all work perfectly, however, what I want to do is have something (anything!) drawn on the QGraphicsScene when the QGraphicsView attached to it is clicked. The widget already exists, so I can't create a new instance of it, I want to use the existing instance. Here is my code so far:

Header File:

namespace Ui {
class MapEditor;
}
 
// Custom implementation of the QGraphicsView widget
// Woo! Event handlers!
class MapViewer : public QGraphicsView
{
    Q_OBJECT
 
public:
    explicit MapViewer(QGraphicsScene *scene, QWidget *parent = 0);
    ~MapViewer();
 
public slots:
    void mousePressEvent(QMouseEvent *event);
 
};
 
// Declaration for the map editor window.
class MapEditor : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MapEditor(QWidget *parent = 0);
    ~MapEditor();
 
public:
    QLayout *editorLayout;
    QPushButton *btn;
    QGraphicsScene *mapScene;
    MapViewer *mapView;
 
private:
    Ui::MapEditor *ui;
};

namespace Ui {
class MapEditor;
}

// Custom implementation of the QGraphicsView widget
// Woo! Event handlers!
class MapViewer : public QGraphicsView
{
    Q_OBJECT

public:
    explicit MapViewer(QGraphicsScene *scene, QWidget *parent = 0);
    ~MapViewer();

public slots:
    void mousePressEvent(QMouseEvent *event);

};

// Declaration for the map editor window.
class MapEditor : public QMainWindow
{
    Q_OBJECT

public:
    explicit MapEditor(QWidget *parent = 0);
    ~MapEditor();

public:
    QLayout *editorLayout;
    QPushButton *btn;
    QGraphicsScene *mapScene;
    MapViewer *mapView;

private:
    Ui::MapEditor *ui;
};

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CPP file:

MapViewer::MapViewer(QGraphicsScene *scene, QWidget *parent) :
    QGraphicsView(scene,parent)
{
 
}
 
MapEditor::MapEditor(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MapEditor)
{
 
    ui->setupUi(this);
    this->setWindowTitle("2DXY :: Map Editor");
    this->setGeometry(10,10,1170,750);
    editorLayout = new QVBoxLayout; // Create a new layout
    this->setLayout(editorLayout); // Set the widget's layout to our newly created layout.
 
    mapScene = new QGraphicsScene(); // Create a new graphics scene to draw upon.
 
    mapView = new MapViewer(mapScene,this); // Create a new graphics view to display our scene - set its parent to 'this' so that it doesn't open in a new window.
    mapView->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    mapView->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    mapView->setGeometry(20,20,1178,546); // Width first, then height.
 
    // Now we're going to draw a grid for our map editor
    int x = 0; // X draw position
    int y = 0; // Y draw position
 
    while(x < 1178)
    {
        mapScene->addLine(x,0,x,546,QPen(QBrush(Qt::red),1)); // Draw a vertical red line
        x = x+32; // Every 32 pixels across.
    }
 
    while(y < 546)
    {
        mapScene->addLine(0,y,1178,y,QPen(QBrush(Qt::red),1)); // Draw a horizontal red line
        y = y+32; // Every 32 pixels downwards.
    }
 
 
    // Test Button!
    btn = new QPushButton(this);
    btn->setText("Hello World!");
    btn->setGeometry(980,610,100,30);
 
    editorLayout->addWidget(btn); //Add the button to the window's layout.
    editorLayout->addWidget(mapView); // Add the QGraphicsView render to the window's layout.
    btn->show(); // Show the button.
    mapView->show(); // Show the QGraphicsView
}
 
void MapViewer::mousePressEvent(QMouseEvent *event)
{
    // Show an empty message box, just to check that the event handler works!
    QMessageBox *notification = new QMessageBox();
    notification->show();
    notification->exec();
 
}

MapViewer::MapViewer(QGraphicsScene *scene, QWidget *parent) :
    QGraphicsView(scene,parent)
{

}

MapEditor::MapEditor(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MapEditor)
{

    ui->setupUi(this);
    this->setWindowTitle("2DXY :: Map Editor");
    this->setGeometry(10,10,1170,750);
    editorLayout = new QVBoxLayout; // Create a new layout
    this->setLayout(editorLayout); // Set the widget's layout to our newly created layout.

    mapScene = new QGraphicsScene(); // Create a new graphics scene to draw upon.

    mapView = new MapViewer(mapScene,this); // Create a new graphics view to display our scene - set its parent to 'this' so that it doesn't open in a new window.
    mapView->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    mapView->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    mapView->setGeometry(20,20,1178,546); // Width first, then height.

    // Now we're going to draw a grid for our map editor
    int x = 0; // X draw position
    int y = 0; // Y draw position

    while(x < 1178)
    {
        mapScene->addLine(x,0,x,546,QPen(QBrush(Qt::red),1)); // Draw a vertical red line
        x = x+32; // Every 32 pixels across.
    }

    while(y < 546)
    {
        mapScene->addLine(0,y,1178,y,QPen(QBrush(Qt::red),1)); // Draw a horizontal red line
        y = y+32; // Every 32 pixels downwards.
    }


    // Test Button!
    btn = new QPushButton(this);
    btn->setText("Hello World!");
    btn->setGeometry(980,610,100,30);

    editorLayout->addWidget(btn); //Add the button to the window's layout.
    editorLayout->addWidget(mapView); // Add the QGraphicsView render to the window's layout.
    btn->show(); // Show the button.
    mapView->show(); // Show the QGraphicsView
}

void MapViewer::mousePressEvent(QMouseEvent *event)
{
    // Show an empty message box, just to check that the event handler works!
    QMessageBox *notification = new QMessageBox();
    notification->show();
    notification->exec();

}

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Any help would be greatly appreciated!

Regards,
Ben.

[wysota]

Where exactly is the problem?

[BnMcG]

Thanks for the reply, however I figured this out!

[amleto]

then why don't you show the solution? Then others who google for a problem and find this thread will also get some benefit!