How to pass parameters via contextmenu addActions() ?

nicholas_yue · wrote on 26 Jan 2022, 05:56

I am trying to find a way to pass some parameters to a slot but am unable to do so, any suggestions?

I am getting the follow errors

QObject::connect: Incompatible sender/receiver arguments
        QAction::triggered(bool) --> WorldGraphicsView::contextMenuHandler(QString,QString)
QObject::connect: Incompatible sender/receiver arguments
        QAction::triggered(bool) --> WorldGraphicsView::contextMenuHandler(QString,QString)

Full source code on github.

Header

#pragma once

#include <QGraphicsView>
#include <QMenu>

class WorldGraphicsView: public QGraphicsView {
    Q_OBJECT
public:
    explicit WorldGraphicsView(QWidget *parent = 0);
    ~WorldGraphicsView();
    virtual void contextMenuEvent(QContextMenuEvent *event) override;
private:
    QMenu* _contextMenu;
private slots:
	void contextMenuHandler(QString parameter1, QString parameter2);
};

Source

#include "WorldGraphicsView.h"

#include <QContextMenuEvent>
#include <QDebug>

WorldGraphicsView::WorldGraphicsView(QWidget *parent)
    : QGraphicsView(parent)
{
	_contextMenu = new QMenu(this);
	QString p1;
	QString p2;

	p1 = "hello";
	p2 = "world";
	QAction* communications = _contextMenu->addAction("communications",this,SLOT(contextMenuHandler(QString,QString)));
	p1 = "star";
	p2 = "war";
	QAction* transport = _contextMenu->addAction("transport",this,SLOT(contextMenuHandler(QString,QString)));
}

WorldGraphicsView::~WorldGraphicsView()
{

}

void WorldGraphicsView::contextMenuEvent(QContextMenuEvent *event)
{
	qDebug() << "WorldGraphicsView::contextMenuEvent";
	_contextMenu->exec(event->globalPos());
}

void WorldGraphicsView::contextMenuHandler(QString parameter1, QString parameter2)
{

}

Christian Ehrlicher · 26 Jan 2022, 16:41

Use a lambda as slot.

nicholas_yue · wrote on 26 Jan 2022, 16:41

@Christian-Ehrlicher said in How to pass parameters via contextmenu addActions() ?:

Use a lambda as slot.

My attempt to use lambda to replace the slot and reading the link, I tried the following but it does not compile

WorldGraphicsView::WorldGraphicsView(QWidget *parent)
    : QGraphicsView(parent)
{
	_contextMenu = new QMenu(this);
	QString p1;
	QString p2;

	p1 = "hello";
	p2 = "world";
	QAction* communications = _contextMenu->addAction("communications",this,
			[=](QString v1, QString v2) { this->contextMenuHandler( p1, p2 ); }
			);

}

Compilation error log

[ 42%] Building CXX object contextmenu/CMakeFiles/cm.dir/WorldGraphicsView.cpp.o
In file included from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtGui/qtguiglobal.h:43:0,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/qtwidgetsglobal.h:43,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/qgraphicsview.h:43,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/QGraphicsView:1,
                 from /home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.h:3,
                 from /home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.cpp:1:
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobject.h: In instantiation of ‘static typename std::enable_if<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) [with Func1 = void (QAction::*)(bool); Func2 = WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>; typename std::enable_if<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1), QMetaObject::Connection>::type = QMetaObject::Connection; typename QtPrivate::FunctionPointer<Func>::Object = QAction]’:
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/qmenu.h:106:9:   required from ‘typename std::enable_if<((! std::is_same<const char*, Func1>::value) && QtPrivate::IsPointerToTypeDerivedFromQObject<T*>::Value), QAction*>::type QMenu::addAction(const QString&, const Obj*, Func1, const QKeySequence&) [with Obj = WorldGraphicsView; Func1 = WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>; typename std::enable_if<((! std::is_same<const char*, Func1>::value) && QtPrivate::IsPointerToTypeDerivedFromQObject<T*>::Value), QAction*>::type = QAction*]’
/home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.cpp:17:4:   required from here
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobject.h:328:9: error: static assertion failed: Signal and slot arguments are not compatible.
         Q_STATIC_ASSERT_X((FunctorArgumentCount >= 0),
         ^
In file included from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobjectdefs.h:50:0,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qmetatype.h:50,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/qgraphicsview.h:44,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/QGraphicsView:1,
                 from /home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.h:3,
                 from /home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.cpp:1:
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobjectdefs_impl.h: In instantiation of ‘struct QtPrivate::FunctorReturnType<WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>, QtPrivate::List<> >’:
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobject.h:331:158:   required from ‘static typename std::enable_if<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1), QMetaObject::Connection>::type QObject::connect(const typename QtPrivate::FunctionPointer<Func>::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) [with Func1 = void (QAction::*)(bool); Func2 = WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>; typename std::enable_if<(QtPrivate::FunctionPointer<Func2>::ArgumentCount == -1), QMetaObject::Connection>::type = QMetaObject::Connection; typename QtPrivate::FunctionPointer<Func>::Object = QAction]’
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/qmenu.h:106:9:   required from ‘typename std::enable_if<((! std::is_same<const char*, Func1>::value) && QtPrivate::IsPointerToTypeDerivedFromQObject<T*>::Value), QAction*>::type QMenu::addAction(const QString&, const Obj*, Func1, const QKeySequence&) [with Obj = WorldGraphicsView; Func1 = WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>; typename std::enable_if<((! std::is_same<const char*, Func1>::value) && QtPrivate::IsPointerToTypeDerivedFromQObject<T*>::Value), QAction*>::type = QAction*]’
/home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.cpp:17:4:   required from here
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobjectdefs_impl.h:371:78: error: no matching function for call to ‘WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>::operator()()’
         typedef decltype(dummy<Functor>().operator()((dummy<ArgList>())...)) Value;
                                                                              ^~~~~
/home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.cpp:16:31: note: candidate: WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>
    [=](QString v1, QString v2 ) { this->contextMenuHandler( p1, p2 ); }
                               ^
/home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.cpp:16:31: note:   candidate expects 2 arguments, 0 provided
In file included from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobjectdefs.h:50:0,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qmetatype.h:50,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/qgraphicsview.h:44,
                 from /home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtWidgets/QGraphicsView:1,
                 from /home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.h:3,
                 from /home/nyue/projects/Qt/QtQuestions/QtQuestions_git/Qt5/contextmenu/WorldGraphicsView.cpp:1:
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobjectdefs_impl.h:451:18: error: ‘QtPrivate::QFunctorSlotObject<Func, N, Args, R>::QFunctorSlotObject(Func) [with Func = WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>; int N = 0; Args = QtPrivate::List<>; R = void]’, declared using local type ‘WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>’, is used but never defined [-fpermissive]
         explicit QFunctorSlotObject(Func f) : QSlotObjectBase(&impl), function(std::move(f)) {}
                  ^~~~~~~~~~~~~~~~~~
/home/nyue/systems/Qt/5.14.2/5.14.2/gcc_64/include/QtCore/qobjectdefs_impl.h:451:18: warning: ‘QtPrivate::QFunctorSlotObject<Func, N, Args, R>::QFunctorSlotObject(Func) [with Func = WorldGraphicsView::WorldGraphicsView(QWidget*)::<lambda(QString, QString)>; int N = 0; Args = QtPrivate::List<>; R = void]’ used but never defined
contextmenu/CMakeFiles/cm.dir/build.make:103: recipe for target 'contextmenu/CMakeFiles/cm.dir/WorldGraphicsView.cpp.o' failed
make[2]: *** [contextmenu/CMakeFiles/cm.dir/WorldGraphicsView.cpp.o] Error 1
CMakeFiles/Makefile2:98: recipe for target 'contextmenu/CMakeFiles/cm.dir/all' failed
make[1]: *** [contextmenu/CMakeFiles/cm.dir/all] Error 2
Makefile:110: recipe for target 'all' failed
make: *** [all] Error 2

Christian Ehrlicher · wrote on 26 Jan 2022, 17:44

Where should the two parameters for your lambda come from? The slot must have the same (or less) number of arguments as the signal, in your case it's 1 or 0 since QAction::triggered() only has bool as a parameter.

nicholas_yue · 26 Jan 2022, 19:44

I got it working.

WorldGraphicsView::WorldGraphicsView(QWidget *parent)
    : QGraphicsView(parent)
{
	_contextMenu = new QMenu(this);
	QString p1;
	QString p2;

	p1 = "hello";
	p2 = "world tomorrow";
	bool s = true;
	QAction* communications = _contextMenu->addAction("communications");
	connect(communications,  &QAction::triggered, this, [this, v1=p1, v2=p2]{ contextMenuHandler(v1,v2); });
}

Christian Ehrlicher · wrote on 26 Jan 2022, 19:44

@nicholas_yue said in How to pass parameters via contextmenu addActions() ?:

[this, v1=p1, v2=p2]{

Why do you want to rename them? A simple [this, p1, p2] is enough.