Why doesn't my QDeclarativeItem get any mouse/keyboard events? - c++

Question

This is a reduced down, minimum complete example demonstrating my problem:
I have an application which hosts a QDeclarativeView; file events.cpp:
#include <QApplication>
#include <QDeclarativeView>
#include "TestItem.h"
int main(int argc,char* argv[]) {
QApplication app(argc,argv);
qmlRegisterType<TestItem>("Testing",1,0,"Tester");
QDeclarativeView page;
page.setSource(QUrl("page.qml"));
Q_ASSERT(page.status()==QDeclarativeView::Ready);
page.show();
return app.exec();
}
That TestItem is a subclassed QDeclarativeItem defined in file TestItem.h:
#ifndef _TestItem_h_
#define _TestItem_h_
#include <iostream>
#include <QDeclarativeItem>
#include <QPainter>
class TestItem : public QDeclarativeItem {
Q_OBJECT
public:
TestItem() {
setFlag(QGraphicsItem::ItemHasNoContents,false);
std::cerr << "[TestItem created]";
}
void paint(QPainter* painter,const QStyleOptionGraphicsItem*,QWidget*) {
painter->drawLine(0,0,width(),height());
painter->drawLine(0,height(),width(),0);
}
protected:
void mousePressEvent(QGraphicsSceneMouseEvent*) {
std::cerr << "[TestItem::mousePressEvent]";
}
void keyPressEvent(QKeyEvent*) {
std::cerr << "[TestItem::keyPressEvent]";
}
};
#endif
and the page.qml file loaded into the QDeclarativeView is simply:
import QtQuick 1.0
import Testing 1.0
Tester {
width: 200
height: 200
}
It's all built (with Qt 4.8 on Debian-Wheezy amd64) with qmake file
CONFIG += debug
QT += core gui declarative
TARGET = events
TEMPLATE = app
SOURCES += events.cpp
HEADERS += TestItem.h
and, once built, when I run ./events I get a window displaying the Tester's painted 'X', as expected:
and a [TestItem created] logged to the console. However, clicking within the window or pressing keys completely fails to invoke either of the mouse or key event handlers.
I'm completely mystified. Is some extra magic (in the C++ or QML domains) needed to get mouse/keyboard events routed to these sort of "plugin" QDeclarativeItem classes? I certainly don't have any problems defining a MouseArea in the QML file and having it do stuff to QML state, and the code this is reduced from has no problems with signals and slots interoperating between the C++ item and QML code... but when it comes to mouse/keyboard events, there's just no sign of them on the C++ side.

Answer 1

To get (left) mouse events, all that is needed is to add
setAcceptedMouseButtons(Qt::LeftButton);
in the TestItem constructor. This is a little surprising as the documentation for the inherited QGraphicsItem::setAcceptedMouseButtons says "By default, all mouse buttons are accepted", but maybe something else in the setup messes with the state.
To get keyboard events, setFocus(true) just needs to be invoked. The documentation seems to imply setFlag(QGraphicsItem::ItemIsFocusable,true) should also be called, but it doesn't actually seem to be necessary in my test.