Initialization of the constructor of a QThread C++ with QString parameter - c++

Question

is it possible to initialize a new QThread with a parameter?? I created two threads in MainWindow. Now i want initialize the Thread "mySave" with a QString. But it doesn't work.
void MainWindow::on_startButton_clicked()
{
thread = new QThread();
mThread = new myThread();
threadSave = new QThread();
mSave = new mySave("HelloWorld");
....
}
I change the line mSave = new mySave() to mySave = new mySave("HelloWorld") and the constructor of mySave-Class to
mySave::mySave(QObject *parent, QString stringFromMainWindow)
: QObject{parent}, m_string{stringFromMainWindow}
{
this->stringMySave = stringFromMainWindow;
}
mySave.h
class mySave : public QObject
{
Q_OBJECT
public:
explicit mySave(QObject *parent = nullptr, QString stringFileName = NULL);
private:
QFile file;
QString m_string {};
....
But i become a fault!
mainwindow.cpp:57:17: error: no matching constructor for initialization of 'mySave'
mysave.h:9:7: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'const char [6]' to 'const mySave' for 1st argument
mysave.h:13:14: note: candidate constructor not viable: no known conversion from 'const char [6]' to 'QObject *' for 1st argument
What's wrong...??
Without QString parameter everthing works fine:
void MainWindow::on_startButton_clicked()
{
thread = new QThread();
mThread = new myThread();
threadSave = new QThread();
mSave = new mySave();
connect(thread, SIGNAL(finished()), mThread, SLOT(deleteLater()));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
connect(mThread, SIGNAL(emitData(const QByteArray &)), this, SLOT(setEditText(const QByteArray &)));
mThread->moveToThread(thread);
thread->start();
mSave->moveToThread(threadSave);
threadSave->start();
QMetaObject::invokeMethod(mThread, "interfaceSerial");
QMetaObject::invokeMethod(mSave, "startFile", Q_ARG(QString, fileName));
qDebug() << "Main open " << QThread::currentThread();
dataTimer.start(0); // Interval 0 means to refresh as fast as possible
}
mySave-Thread constructor
mySave::mySave(QObject *parent)
: QObject{parent}
{
qDebug() << "Thread open " << QThread::currentThread();
}
How can i set a QString parameter in the constructor of a new QThread....??
Thanks & Bye bye

Answer 1

The problem was solved...you have to write
class mySave : public QObject
{
Q_OBJECT
public:
explicit mySave(QString stringFileName = NULL, QObject *parent = nullptr);
private:
QFile file;
The last parameter has to be the QObject!!

Answer 2

Look at your mySave constructor signature...
explicit mySave(QObject *parent = nullptr, QString stringFileName = NULL);
The first parameter passed must be a QObject * (or something implicitly convertible to a QObject *) and the second parameter passed must be a QString. If you want mySave to be constructible using a QString only then you must provide a suitable constructor. The obvious option would be to simply reverse the order of the passed parameters...
explicit mySave(QString stringFileName = QString(), QObject *parent = nullptr);
Having said that, the most commonly used constructor calls for classes of this nature would probably be...
/* Default constructor: no text or parent. */
mySave ms1;
/* Text only. */
mySave ms2("Some text...");
/* Parent object only. */
QObject *parent = ...;
mySave ms3(parent);
/* Pass both text and parent object. */
mySave ms4("Some text...", parent);
All of these cases can be provided by the following two constructors...
mySave::mySave (const QString &stringFileName = QString(), QObject *parent = nullptr)
: QObject(parent)
, m_string(stringFileName)
{
...
}
mySave::mySave (QObject *parent)
: QObject(parent)
{
...
}
Or, if you prefer, make the second a delegating constructor...
mySave::mySave (QObject *parent)
: mySave(QString(), parent)
{}