Very Simple QGraphicsView Example for QT5.7 QtCreator mainwindow's main.cpp

[mdavidjohnson]

Could someone please point me to a very simple QGraphicsView Example for QT5.7 QtCreator mainwindow's main.cpp that actually works and doesn't throw a "no matching function for call" error.

I've read the documentation for QGraphicsView, QGraphicsScene, and QGraphicsItem. I've tried various code published here and elsewhere which is supposed to work. But everything seems to throw that error.

For example, I start a new Qt widgets application in Qt Creator. I change nothing except main.cpp, which becomes:

#include "mainwindow.h"
#include <QApplication>
#include <QGraphicsItem>
#include <QGraphicsScene>
#include <QGraphicsView>
 
int main( int argc, char **argv )
{
    QApplication app(argc, argv);
 
    QGraphicsScene scene;
    QGraphicsRectItem *rect = scene.addRect(QRectF(0, 0, 100, 100));
 
    QGraphicsItem *item = scene.itemAt(50, 50);
    // item == rect
 
    QGraphicsView view(&scene);
    view.show();
 
    return app.exec();
}

#include "mainwindow.h"
#include <QApplication>
#include <QGraphicsItem>
#include <QGraphicsScene>
#include <QGraphicsView>

int main( int argc, char **argv )
{
    QApplication app(argc, argv);

    QGraphicsScene scene;
    QGraphicsRectItem *rect = scene.addRect(QRectF(0, 0, 100, 100));

    QGraphicsItem *item = scene.itemAt(50, 50);
    // item == rect

    QGraphicsView view(&scene);
    view.show();

    return app.exec();
}

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At the line:

QGraphicsItem *item = scene.itemAt(50, 50);

QGraphicsItem *item = scene.itemAt(50, 50);

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I get "no matching function for call to 'QGraphicsScene::itemAt(int,int)'.

[anda_skoa]

The compiler gave you the reason it couldn't compile this.

There is no such method.

You are probably trying to call this one http://doc.qt.io/qt-5/qgraphicsscene.html#itemAt-3

If you look at the full error message, it even tells you why it couldn't select that one

/dvl/Qt5.7.0/5.7/gcc_64/include/QtWidgets/qgraphicsscene.h:179:27: note: candidate: QGraphicsItem* QGraphicsScene::itemAt(qreal, qreal, const QTransform&) const
inline QGraphicsItem *itemAt(qreal x, qreal y, const QTransform &deviceTransform) const
^
/dvl/Qt5.7.0/5.7/gcc_64/include/QtWidgets/qgraphicsscene.h:179:27: note: candidate expects 3 arguments, 2 provided

Cheers,
_

[mdavidjohnson]

Thank you -

I'll look into that.

But, my copy of Qt 5.7 QtCreator 4.0.2 didn't give me all of that error message. All I got was:

"C:\work\Qt5Work\Qt570\LearningTests\QGraphicsView FirstTest\main.cpp:14: error: no matching function for call to 'QGraphicsScene::itemAt(int, int)'
QGraphicsItem *item = scene.itemAt(50, 50);"

Is there some setting I need to adjust to get the more verbose error messages?

[anda_skoa]

Error messages depend on the compiler.
In my case that is g++ 5.3.1

Did you look at the compile output or just the issues tab?

Cheers,
_