Problem in MouseMoveEvent

[jpn]

#include <QtGui>
 
class MainWindow : public QMainWindow
{
public:
	MainWindow(QWidget* parent = 0) : QMainWindow(parent)
	{
		QGraphicsScene* scene = new QGraphicsScene;
		QGraphicsItem* item = scene->addText("Item");
		item->setFlag(QGraphicsItem::ItemIsMovable); 
 
		view = new QGraphicsView(scene);
		view->viewport()->installEventFilter(this);
		// this is not actually even needed, QGraphicsView 
		// already sets the mouse tracking on on it's viewport
		view->viewport()->setMouseTracking(true);
		setCentralWidget(view);
	}
 
	bool eventFilter(QObject* object, QEvent* event)
	{
		if (event->type() == QEvent::MouseMove)
		{
			QMouseEvent* mouse = static_cast<QMouseEvent*>(event);
			QPointF pos = view->mapToScene(mouse->pos());
			statusBar()->showMessage(QString("(%1,%2)").arg(pos.x()).arg(pos.y()));
		}
		return false;
	}
 
private:
	QGraphicsView* view;
};
 
int main(int argc, char* argv[])
{
	QApplication app(argc, argv);
	MainWindow w;
	w.show();
	return app.exec();
}

#include <QtGui>

class MainWindow : public QMainWindow
{
public:
	MainWindow(QWidget* parent = 0) : QMainWindow(parent)
	{
		QGraphicsScene* scene = new QGraphicsScene;
		QGraphicsItem* item = scene->addText("Item");
		item->setFlag(QGraphicsItem::ItemIsMovable); 
		
		view = new QGraphicsView(scene);
		view->viewport()->installEventFilter(this);
		// this is not actually even needed, QGraphicsView 
		// already sets the mouse tracking on on it's viewport
		view->viewport()->setMouseTracking(true);
		setCentralWidget(view);
	}

	bool eventFilter(QObject* object, QEvent* event)
	{
		if (event->type() == QEvent::MouseMove)
		{
			QMouseEvent* mouse = static_cast<QMouseEvent*>(event);
			QPointF pos = view->mapToScene(mouse->pos());
			statusBar()->showMessage(QString("(%1,%2)").arg(pos.x()).arg(pos.y()));
		}
		return false;
	}

private:
	QGraphicsView* view;
};

int main(int argc, char* argv[])
{
	QApplication app(argc, argv);
	MainWindow w;
	w.show();
	return app.exec();
}

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[wysota]

Subclassing the view and ignoring its mouse events (one has to specifically call ignore() on the event object in mouse event handlers) should work as well.

[aamer4yu]

@jpn

Thanks, ur solution is working fine...also the movement of items is smooth

I was also pretty much using the same code...

class CMainWindow : public QMainWindow
{
    Q_OBJECT
public:
    CMainWindow(QWidget *parent=0);
	~CMainWindow();
 
private:
    //void setupMatrix();
    void populateScene();
 
    CViewFrame *viewFrame;	 // CViewFrame derived from QFrame
 
    //QGraphicsScene *scene;
    CScene *scene;
	QList<CMacro*> macroList;
 
protected:
	bool eventFilter(QObject *obj, QEvent *event);
	void mouseMoveEvent ( QMouseEvent * event );
	void paintEvent(QPaintEvent *event);
};
 
 
CMainWindow::CMainWindow(QWidget *parent)
    : QMainWindow(parent)
{
	setMouseTracking(true);
 
    populateScene();
 
 
    viewFrame = new CViewFrame("demo",this);
    viewFrame->getView()->setScene(scene);
	viewFrame->getView()->setMouseTracking(true);
 
	viewFrame->getView()->setSceneRect(-100,-100,1700,2500);
	//setContentsMargins(200,200,600,600);
 
	//scene->setBackgroundBrush(Qt::blue);
 
 
	setCentralWidget(viewFrame);
	viewFrame->getView()->installEventFilter(this);
	//viewFrame->getView()->installEventFilter(this);
....
...
...

class CMainWindow : public QMainWindow
{
    Q_OBJECT
public:
    CMainWindow(QWidget *parent=0);
	~CMainWindow();
    
private:
    //void setupMatrix();
    void populateScene();

    CViewFrame *viewFrame;	 // CViewFrame derived from QFrame

    //QGraphicsScene *scene;
    CScene *scene;
	QList<CMacro*> macroList;

protected:
	bool eventFilter(QObject *obj, QEvent *event);
	void mouseMoveEvent ( QMouseEvent * event );
	void paintEvent(QPaintEvent *event);
};


CMainWindow::CMainWindow(QWidget *parent)
    : QMainWindow(parent)
{
	setMouseTracking(true);

    populateScene();


    viewFrame = new CViewFrame("demo",this);
    viewFrame->getView()->setScene(scene);
	viewFrame->getView()->setMouseTracking(true);

	viewFrame->getView()->setSceneRect(-100,-100,1700,2500);
	//setContentsMargins(200,200,600,600);

	//scene->setBackgroundBrush(Qt::blue);


	setCentralWidget(viewFrame);
	viewFrame->getView()->installEventFilter(this);
	//viewFrame->getView()->installEventFilter(this);
....
...
...

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The only mistake was i was installing filter on view... rather than viewport
The events are now captured in QEvent::MouseMove of the filter...

So what does actually viewport act like ? why doesnt installing filter on view capture the events ??



@wysota

Ur solution too is working and short & elegant
Can u tell me more on event delegation ?? I saw thru the call stack and came to conclude that...that Qt uses QApplicationPrivate::notify_helper() to properly distrubute the events, and hence its View in the window that receives the events first.

but what will ignore do and how will the events propogate further ?? can u throw more light ?


Thanks a lot both of u guys...just wondering what took u so long to answer
neways it helped me in exploring & learning myself.

Thx again

[wysota]

Ur solution too is working and short & elegant

It wasn't my solution. Jpn already told you about it in his second post in this thread.

Can u tell me more on event delegation ?? I saw thru the call stack and came to conclude that...that Qt uses QApplicationPrivate::notify_helper() to properly distrubute the events, and hence its View in the window that receives the events first.

I can, but I doubt I can tell you more than you can read from the docs. In general the mechanism is simmilar to the one present in (for example) MFC - the events are propagated from class to class until one of them marks them as handled. In case of Qt the order is child widget -> its parent -> its parent -> ... -> application object.

but what will ignore do and how will the events propogate further ?? can u throw more light ?

I think I already answered that

Thanks a lot both of u guys...just wondering what took u so long to answer

Your question was answered at the very beginning, you just ignored that answer (instead of ignoring the event).

[aamer4yu]

Your question was answered at the very beginning, you just ignored that answer (instead of ignoring the event).

No, I didnt ignore that... as i said i installed filter on view...and tried all sort of things
i didt knew i had to install them on viewport...

earlier answers were like showing which tool to use... but didnt tell where to use
or may b i was ameatuer in Qt that i didnt understand what they meant

[wysota]

Following the "ignore the event" link in JPN's post would have lead you to the right answer - event propagation.

[aamer4yu]

well i said, I had tried that too... but might be making some mistake somewhere...

neways dont fight... I take my thanks back from u ...
Jpn... double thnks to u

is that fine now wysota :P

[wysota]

is that fine now wysota :P

It's your call.

[ranjithreddykommareddy]

hii....wysota .i am also having same problem with mouse events .now i am getting mouse events fine in QGraphicsscene .but i want to add a push button in form for mouse events to draw rectangle and it is moveble .so how can i proceed ..? can any one have idea...?

[wysota]

hii....wysota .i am also having same problem with mouse events .now i am getting mouse events fine in QGraphicsscene .but i want to add a push button in form for mouse events to draw rectangle and it is moveble .so how can i proceed ..? can any one have idea...?

Show your (relevant) code, please.

[ranjithreddykommareddy]

thanks for reply
bool Widget:: eventFilter(QObject* object, QEvent* event)
{


if (event->type() == QEvent::MouseButtonPress)
{
QMouseEvent* mouse = static_cast<QMouseEvent*>(event);
if (ui->graphicsView->geometry().contains(mouse->pos()))
{
originpos = ui->graphicsView->mapToScene(mouse->pos());
// qDebug() << mouse->pos() << originpos ;
mousepress = true;
}
//statusBar()->showMessage(QString("(%1,%2)").arg(pos.x()).arg(p os.y()));


}
if(mousepress)
{
if (event->type() == QEvent::MouseMove)

{


QMouseEvent* mouse = static_cast<QMouseEvent*>(event);

if (ui->graphicsView->geometry().contains(mouse->pos()))
{
currentpos = ui->graphicsView->mapToScene(mouse->pos());
//qDebug() << mouse->pos() ;



if(!itemToDraw)
{
itemToDraw = new QGraphicsRectItem;

ui->graphicsView->scene()->addItem(itemToDraw);
itemToDraw->setPen(QPen(Qt::black, 1, Qt::SolidLine));


//itemToDraw->setPos(pos);
}
itemToDraw->setRect(originpos.x(),originpos.y(),
currentpos.x()- originpos.x(),
currentpos.y() - originpos.y());



}
//itemToDraw->setFlag(QGraphicsRectItem::ItemIsMovable);
}


}



if(mousepress)
{
if(event->type() == QEvent::MouseButtonRelease )
{
QMouseEvent* mouse = static_cast<QMouseEvent*>(event);
QPointF pos = ui->graphicsView->mapToScene(mouse->pos());
// qDebug() << pos ;
mousepress = false;

}
}



}