Can't pass QMap through to SLOT

Question

So, this works:

.h

public slots:
void addMenu(QString passedName);

signals:
void clicked(const QString &text);

.cpp

signalMapper = new QSignalMapper(this);
signalMapper->setMapping(button, QString("passed_value"));
connect(button, SIGNAL(clicked()), signalMapper, SLOT(map()));
connect(signalMapper, SIGNAL(mapped(QString)), this, SLOT(addMenu(QString)));

Now, I am trying to pass a QMap < QString, QString > through to addMenu instead of just a QString, but I get the error: no matching function for call to 'QSignalMapper::setMapping'. Do I need to create a typeDef or something?

.h

public slots:
void addMenu(QMap < QString, QString > map);

signals:
void clicked(const QMap < QString, QString > &map);

.cpp

//map is defined above

signalMapper = new QSignalMapper(this);
signalMapper->setMapping(button, map);
connect(button, SIGNAL(clicked()), signalMapper, SLOT(map()));
connect(signalMapper, SIGNAL(mapped(QObject*)), this, SLOT(addMenu(QMap < QString, QString >)));

EDIT: I also tried adding a typeDef, but still getting same error.

.h

public:
typedef QMap < QString, QString > passedMapType;

public slots:
void addMenu(passedMapType map);

signals:
void clicked(passedMapType map);

.cpp

passedMapType passedMap;
passedMap.insert(QString("key"), QString("value"));

signalMapper = new QSignalMapper(this);
signalMapper->setMapping(button, passedMap);
connect(button, SIGNAL(clicked()), signalMapper, SLOT(map()));
connect(signalMapper, SIGNAL(mapped(QObject*)), this, SLOT(addMenu(passedMapType));

....

addMenu(passedMapType passedMap) {

}

Answer 1

"Now, I am trying to pass a QMap < QString, QString > through to addMenu instead of just a QString, but I get the error: no matching function for call to 'QSignalMapper::setMapping'."

That's not a general signal/slot or macro expansion problem, but a limitation of QSignalMapper. You can't pass a QMap to setMapping, only int, QString, QWidget* and QObject*. See the QSignalMapper documentation.

connect(signalMapper, SIGNAL(mapped(QObject*)), this, SLOT(addMenu(passedMapType));

That wouldn't work either, because the signatures are incompatible: QObject* vs. QMap.

What I would do: Hold a QMap<QObject*,PassedMapType> in the owner of the buttons, create a slot slotClicked(QObject*) there, connected to the clicked() signals of the buttons, and then look up the PassedMapType object from the map, using the passed QObject*. Edit: added some pseudo code to illustrate it:

QMap<QWidget*, QMap<QString, QString> > map; //member of the class

//when creating the buttons:

for each button b:
    signalMapper->setMapping( b, b );
    map.insert( b, someMapForThisButton );
connect( signalMapper, SIGNAL(mapped(QWidget*)), this, SLOT(addMenuForButton(QWidget*)) );

//the slot:
void addMenuForButton(QWidget* w) {
     const QMap<QString, QString> m = map.value( w );
     create menu...
}

Answer 2

Use typedefs. My feeling is that the comma between the two QString template parameters is a problem in macro expansion.

Answer 3

As a nice work around you can use QObject. QObject has an embedded QMap inside. Here is how it goes:

void sender() {
  ...
  ...
  QObject *data = new QObject(0);
  data->setProperty("Name","xxxx");
  data->setProperty("Address","yyyy");

  //You can also send QImage
  QImage image;
  ...
  data->setProperty("Image",image);

  emit dataReady(data);
 }

signals:
  void dataReady(QObject*);

public slots:
  void receiver(QObject *data) {
    QString Name = data->property("Name").toString();
    QString Address = data->property("Address").toString();
    QImage image = data->property("Image").value<QImage>();
    data->deleteLater();
  }

Answer 4

This is a pure guess, but you may need to use pointer types instead? I never had very much luck passing by reference with &.

public slots:
void addMenu(QMap<QString, QString> *map);

signals:
void clicked(QMap<QString, QString> *map);

Answer 5

The signal and slot must have the same argument types (it's a function call, of sorts), so this line is wrong:

connect(signalMapper, SIGNAL(mapped(QObject*)), this, SLOT(addMenu(passedMapType));

You might need to rethink your logic a bit to make that work.