How to pass a parameter using QSignalMapper, incompatible sender/receiver arguments - c++

Question

Implementation:
void Test::addProcessToList(const QString &command, const QString &id, const BasicInfo &basicInfo) {
QProcess *console = new QProcess();
QSignalMapper* signalMapper = new QSignalMapper (this) ;
connect (console, SIGNAL(readyRead()), signalMapper, SLOT(map())) ;
connect (console, SIGNAL(finished(int)), signalMapper, SLOT(processFinished(int))) ;
signalMapper->setMapping (console, id) ;
connect (signalMapper, SIGNAL(mapped(int)), this, SLOT(pidOut(QString))) ;
console->start(command);
}
void Test::registerProcess(QString id) {
QProcess *console = qobject_cast<QProcess*>(QObject::sender());
QByteArray processOutput = console->readAll();
int mainPID = parsePID(processOutput);
BasicInfo basicInfo;
qDebug() << "Registering id: " + id + " mainPID: " + mainPID;
if(mainPID != 0) {
Main::getInstance()->addProcessToList(mainPID, packageId, basicInfo);
} else {
qWarning() << "pidOut Error fetching mainPID";
}
}
void Test::processFinished(int exitCode) {
QProcess *console = qobject_cast<QProcess*>(QObject::sender());
QByteArray processOutput = console->readAll() + QString("Finished with code %1").arg(exitCode).toLatin1();
qDebug() << " processFinished: " + processOutput;
}
prototypes:
private
void addProcessToList(const QString &command, const QString &id, const BasicInfo &basicInfo);
private slots:
void registerProcess(QString);
void processFinished(int);
I get this errors when I call connect, which tells me I'm doing it wrong:
"QObject::connect: Incompatible sender/receiver arguments
QSignalMapper::mapped(int) --> Test::registerProcess(QString)"
I'm not understanding where I'm suppose to specify my parameter (QString id) so that registerProcess will receive it when it's called? I'm assuming I'm doing this part wrong, cut from above:
signalMapper->setMapping (console, id) ;
connect (signalMapper, SIGNAL(mapped(int)), this, SLOT(pidOut(QString))) ;

Answer 1

QSignalMapper can emit either mapped(const QString & text) or mapped(int i) signals. The type is defined by setMapping(QObject * sender, int id) or setMapping(QObject * sender, const QString & text).
That led to confusion probably by autocompletion in
connect (signalMapper, SIGNAL(mapped(int)), this, SLOT(pidOut(QString)));
The types of signal and slot must be the same for connection.
You set string mapping (QString &id), so the signal in the connection should be QString:
connect (signalMapper, SIGNAL(mapped(QString)), this, SLOT(pidOut(QString)));
Update
After deeper review of the code flow I suspect that you wanted to connect mapper to registerProcess() slot instead of pidOut(). In that slot you can have as an argument QString id that was passed to signalMapper in setMapping() call. That is the purpose of using QSignalMapper.
However, beside that id it is not possible to extract console pointer, since in that case sender() is signalMapper object. If it is the case, QSignalMapper cannot help you here. You should use direct connection of console and this on readReady (of course with slot of this with void argument as readReady()). To get the string id in that slot it is possible to use simple QMap<QProces*, QString> map stored as a Test class member.
// addProcessToList(...):
map[console] = id;
//registerProcess():
QString id = map[console];
//processFinished(...):
map.remove(console);
By the way, it is not needed to created a new instance of QSignalMapper for each map item.