Extract menu action data in receiving function or slot - c++

Question

In my menu, I am setting data to the menu actions. How can I extract that data in my slot? Or even better, instead of connecting a slot, can I also connect a member function that is able to extract the action data (like in the 1st connect)? The action data is meant to identify each action. As a sidenode, I am not sure if I can use several menu action entries on only one openNote-action.
void Traymenu::createMainContextMenu() {
QAction *actionNewNote = m_mainContextMenu.addAction("Neue Notiz");
actionNewNote->setIcon(QIcon("C:\\new.ico"));
actionNewNote->setIconVisibleInMenu(true);
QObject::connect(actionNewNote,&QAction::triggered,this,&Traymenu::newNote);
QString menuEntryName;
QAction *openNote;
QVariant noteID;
for (int i = 0; i<m_noteList.count(); i++) {
std::string noteTitle = m_noteList[i].data()->getTitle();
menuEntryName = QString::fromStdString(noteTitle);
openNote = m_mainContextMenu.addAction(menuEntryName);
connect(openNote,SIGNAL(triggered()),this,SLOT(s_showNote()));
noteID.setValue(m_noteList[i].data()->getID());
openNote->setData(noteID);
}
m_mainIcon.setContextMenu(&m_mainContextMenu);
}
And the slot:
void Traymenu::s_showNote() {
QObject* obj = sender();
//int noteID = data.toInt();
//Search all notes in noteList for that ID and show it
}

Answer 1

Using QObject::sender()
You can use QObject::sender() to get the signal's sender, followed by qobject_cast to cast the sender pointer to the right type.
void Traymenu::s_showNote()
{
QAction* act = qobject_cast<QAction *>(sender());
if (act != 0)
{
QVariant data = act->data();
int noteID = data.toInt();
showNote(noteID); // isolate showNote logic from "get my ID" stuff
}
}
void Traymenu::showNote(int noteID)
{
// Do the real work here, now that you have the ID ...
}
As the Qt documentation warns, "This function violates the object-oriented principle of modularity." It's still a fairly safe and standard practice, though — just one with some shortcomings. In particular, note that you're committing to having a s_showNote method that only works when it's accessed as a slot (otherwise sender is 0).
Using QSignalMapper
Alternatively, you can use the QSignalMapper class to return a pointer to teh item or to associate a unique identifier (int or QString) with each item.
Something like this:
void Traymenu::createMainContextMenu()
{
signalMapper = new QSignalMapper(this); // (or initialize elsewhere)
// ... (create your newNote here same as before) ...
QString menuEntryName;
QAction *openNote;
int noteID;
for (int i = 0; i<m_noteList.count(); i++) {
std::string noteTitle = m_noteList[i].data()->getTitle();
menuEntryName = QString::fromStdString(noteTitle);
openNote = m_mainContextMenu.addAction(menuEntryName);
noteID = m_noteList[i].data()->getID();
openNote->setData(QVariant(noteID)); // (if you still need data in the QActions)
signalMapper->setMapping(openNote, noteID);
}
connect(signalMapper, SIGNAL(mapped(int)),
this, SLOT(showNote(int)));
m_mainIcon.setContextMenu(&m_mainContextMenu);
}
void Traymenu::showNote(int noteID) {
// Now you have the ID ...
}
This pattern has the benefit of isolating all the ugly "Wait, how do I get my identifier?" stuff in one spot, instead of having both the initialization code and the slot function having code for associating actions and IDs.

Answer 2

I would write it like:
void Traymenu::s_showNote() {
QObject* obj = sender();
QAction *action = qobject_cast<QAction *>(obj);
int id = action->data().toInt();
for (int i = 0; i < m_noteList.count(); i++) {
if (m_noteList[i].data()->getID() == id) {
[..]
}
}
}