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) {

}

score 3 · Answer 1 · answered Nov 19 '10 at 20:36

3

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

answered Nov 19 '10 at 20:36

Cătălin Pitiș

14,123
2
39
62

The comma is what caused the issue. I've run into this before. – Timothy Baldridge Nov 19 '10 at 20:53
Hmmm...I tried adding a typedef, but I still get the same error. Am I missing something? Code is above. – Nov 19 '10 at 21:10
If you're going to a use a typedef, don't forget to call qRegisterMetaType before trying to connect. – JoshL Oct 29 '14 at 20:10

Frank Osterfeld · Accepted Answer · 2010-11-21T01:03:41.213

"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...
}

I will give this a shot; This seems like it should be an easier process. — , Nov 19 '10 at 21:45
This doesn't seem as straightforward as it should, have you seen any examples for this? — , Nov 19 '10 at 23:43

score 1 · Answer 3 · answered Mar 08 '14 at 03:22

1

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();
  }

answered Mar 08 '14 at 03:22

Omid Sakhi

140
1
5

Great idea, I like this approach! – sidewinderguy Jun 08 '17 at 21:48
One concern I have is: if there are multiple slots that the 'dataReady' signal is connected to, then won't each of them do a 'data->deleteLater()'? And if so, would that cause a double-delete issue? – sidewinderguy Jun 08 '17 at 21:49
According to the docs on deleteLater(): "Note: It is safe to call this function more than once; when the first deferred deletion event is delivered, any pending events for the object are removed from the event queue." I guess that answers my question. I guess as long as all the slots get called from the event loop before it hits the deleteLater() then it's fine, which I think is the case? – sidewinderguy Jun 08 '17 at 21:59

score 0 · Answer 4 · answered Nov 19 '10 at 20:28

0

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);

answered Nov 19 '10 at 20:28

jocull

20,008
22
105
149

Qt containers should be passed by const reference, not by pointer. Especially with signal and slots, one runs into all kinds of ownership problems (think queued connections - who deletes the map then?) when using pointers. – Frank Osterfeld Nov 19 '10 at 21:16

score 0 · Answer 5 · answered Nov 19 '10 at 22:24

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.

Can't pass QMap through to SLOT

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