Subclassing from QGraphicsTextItem and QScrollArea issue

[sreenidhi707]

Hello Everyone

I want to create a main window with a scrollable QGraphicsScene which has objects subclassed from QGraphicsTextItem. Basically, I want to draw a white rectangle with text inside it (the code to draw text inside the rectangle is not shown), and when the rectangle is bigger than the viewport, I want scroll bars to automatically appear in the QGraphicsScene

In the code snippets below I have simplified the code with just one object of MyGraphicsTextItem in the QGraphicsScene object. All I see with the code below is a blank screen, the overridden MyGraphicsTextItem:: paint() does not get called.

mainwindow.h

namespace Ui {
class MainWindow;
}
 
class MyGraphicsTextItem : public QGraphicsTextItem
{
    Q_OBJECT
public:
    explicit MyGraphicsTextItem()
    {
 
    };
    ~MyGraphicsTextItem(){};
 
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
};
 
class MyWidget : public QWidget
{
    Q_OBJECT
 
public:
    explicit MyWidget(QWidget *_parent = nullptr) :
        QWidget(_parent)
    {
        parent = _parent;
 
        RenderScene();
 
 
    };
 
    ~MyWidget(){};
 
    QWidget* parent = nullptr;
    QGraphicsScene* graphicsScene = nullptr ;
    QScrollArea* scrollArea = nullptr;
    void RenderScene();
 
};
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
 
private:
    Ui::MainWindow *ui;
 
    MyWidget* myWidget = nullptr;
};

namespace Ui {
class MainWindow;
}

class MyGraphicsTextItem : public QGraphicsTextItem
{
    Q_OBJECT
public:
    explicit MyGraphicsTextItem()
    {

    };
    ~MyGraphicsTextItem(){};

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
};

class MyWidget : public QWidget
{
    Q_OBJECT

public:
    explicit MyWidget(QWidget *_parent = nullptr) :
        QWidget(_parent)
    {
        parent = _parent;

        RenderScene();


    };

    ~MyWidget(){};

    QWidget* parent = nullptr;
    QGraphicsScene* graphicsScene = nullptr ;
    QScrollArea* scrollArea = nullptr;
    void RenderScene();

};

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

    MyWidget* myWidget = nullptr;
};

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mainwindow.cpp

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    myWidget = new MyWidget(this);
 
    this->setCentralWidget(myWidget);
 
}
 
 
void MyWidget::RenderScene()
{
    graphicsScene = new QGraphicsScene(this);
 
    MyGraphicsTextItem* graphicsTextItem = new MyGraphicsTextItem();
    graphicsScene->addItem(graphicsTextItem);
 
    QGraphicsView* graphicsView = new QGraphicsView(this);
    graphicsView->setScene(graphicsScene);
 
    scrollArea = new QScrollArea();
 
    QHBoxLayout* scrollLayout = new QHBoxLayout();
    scrollArea->setLayout(scrollLayout);
 
    scrollArea->setWidget(graphicsView);
    scrollArea->setWidgetResizable(true);
 
 
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MyGraphicsTextItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    cout << "Paint called\n";
    QRect pixelRect(0, 0, 500, 500);
 
    QPainterPath painterPath;
    painterPath.addRect(pixelRect);
 
    painter->setPen(Qt::black);
    painter->setRenderHint(QPainter::Antialiasing);
 
    painter->fillPath(painterPath, Qt::white);
 
    QGraphicsTextItem::paint(painter,option,widget);
}

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

    myWidget = new MyWidget(this);

    this->setCentralWidget(myWidget);

}


void MyWidget::RenderScene()
{
    graphicsScene = new QGraphicsScene(this);

    MyGraphicsTextItem* graphicsTextItem = new MyGraphicsTextItem();
    graphicsScene->addItem(graphicsTextItem);

    QGraphicsView* graphicsView = new QGraphicsView(this);
    graphicsView->setScene(graphicsScene);

    scrollArea = new QScrollArea();

    QHBoxLayout* scrollLayout = new QHBoxLayout();
    scrollArea->setLayout(scrollLayout);

    scrollArea->setWidget(graphicsView);
    scrollArea->setWidgetResizable(true);


}

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

void MyGraphicsTextItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    cout << "Paint called\n";
    QRect pixelRect(0, 0, 500, 500);

    QPainterPath painterPath;
    painterPath.addRect(pixelRect);

    painter->setPen(Qt::black);
    painter->setRenderHint(QPainter::Antialiasing);

    painter->fillPath(painterPath, Qt::white);

    QGraphicsTextItem::paint(painter,option,widget);
}

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On the other hand, if I change this

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

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

    myWidget = new MyWidget(this);

    this->setCentralWidget(myWidget);

}

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to this

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    myWidget = new MyWidget(this);
 
    this->setCentralWidget(myWidget->scrollArea);
 
}

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

    myWidget = new MyWidget(this);

    this->setCentralWidget(myWidget->scrollArea);

}

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I can see the white rectangle, however I don't get scrollbars in the window.
Screen Shot 2019-01-06 at 5.10.59 PM.jpg