Qt: How to adjust QGraphicsItem to dynamicaly change size - c++

Question

I've this problem for several days. I have created QGraphicsItem and I want to stretch/adjust it's size to size of my QGraphicsView. I was using paint() method, but got with it problems with updating. Now I've used boundingRect() but it uses fixed size. When I set too big size it expand my scene and scrollbars are appearing. Is there way to adjust size of item to size of View?
EDIT: I want only adjust height of my object.
Here's some code:
Header of my Item:
#ifndef POINTER_H
#define POINTER_H
#include <QObject>
#include <QColor>
#include <QRect>
#include <QGraphicsLineItem>
#include <QPainter>
#include <QGraphicsSceneMouseEvent>
class Pointer : public QGraphicsLineItem
{
public:
Pointer();
void paint(QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget);
QRectF boundingRect() const;
int position;
void changePosition(int x);
};
#endif // TRACKPOINTER_H
Implementation of my Item:
#include "pointer.h"
Pointer::Pointer()
{
//this->setFlag(QGraphicsLineItem::ItemIsMovable);
//setFlag(QGraphicsLineItem::ItemIsFocusable);
//setFocus();
}
void Pointer::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
QPen pen(Qt::red);
painter->setPen(pen);
painter->setBrush(QColor(77,77,77));
painter->drawLine(0,0,0,2000);
}
QRectF Pointer::boundingRect() const
{
return QRectF(0,0,2,600);
}
void Pointer::changePosition(int x)
{
//position = x;
setPos(x,0);
update();
}
And my Window:
Window::Window(Timers *timer, TrackPointer *tp)
{
Timeline = new QGraphicsScene(this);
TimelineView = new QGraphicsView(Timeline);
TimelineView->setAlignment(Qt::AlignTop|Qt::AlignLeft);
QVBoxLayout *timeLineLayout = new QVBoxLayout;
timeLineLayout->addWidget(TimelineView);
Pointer *pointer = new Pointer;
Timeline->addItem(pointer);
}
I have also problems with my scene: When my object moves somewhere away - it expand scene. Later when I bring my object back to it's starting position scene still is expanded and I have scrollbars to scroll my view around the scene. Is there way to decrease scene size using my object?

Answer 1

The promised example looks something like this:
MainWindow.h
#include <QMainWindow>
class QGraphicsView;
class QGraphicsRectItem;
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = nullptr);
bool eventFilter(QObject *watched, QEvent *event) override;
private:
QGraphicsView *m_view;
QGraphicsRectItem *m_item;
};
MainWindow.cpp
#include "MainWindow.h"
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsRectItem>
#include <QEvent>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
m_view(new QGraphicsView(this)),
m_item(new QGraphicsRectItem(0, 0, 1, 1))
{
m_view->setScene(new QGraphicsScene());
m_view->setFrameStyle(QFrame::NoFrame);
m_view->setAlignment(Qt::AlignLeft | Qt::AlignTop);
m_view->setSceneRect(0, 0, 1, 1);
m_view->installEventFilter(this);
m_view->scene()->addItem(m_item);
setCentralWidget(m_view);
resize(600, 400);
}
bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
if ((watched == m_view) && (event->type() == QEvent::Resize))
m_item->setRect(m_view->viewport()->rect().adjusted(5, 5, -5, -5));
return QMainWindow::eventFilter(watched, event);
}

Answer 2

look into :QGraphicsView::fitInView
http://doc.qt.io/qt-4.8/qgraphicsview.html#fitInView
QPixmap *pixMap= new QPixmap();;
QGraphicsScene *scene=new QGraphicsScene();;
pixMap->loadFromData(jpegData);
scene->clear();
pixMapItem = scene->addPixmap(*pixMap);
ui->graphicsView->fitInView(scene->sceneRect(), Qt::KeepAspectRatio);
ui->graphicsView->show();
ui->graphicsView->viewport()->update();