Qt - connecting a signal/slot in a triggered action - c++

Question

I'm using Qt 5 on a Windows and building a GUI App with multiple QDialog classes. I am trying to connect a signal from a QDialog in a triggered action of the QMainWindow class after instances of both have been created. I have read the documentation on Qt here: http://doc.qt.io/qt-4.8/signalsandslots.html and here: https://wiki.qt.io/New_Signal_Slot_Syntax. I have also read through many questions on stackoverflow that have helped correct some of the initial errors I was getting, but haven't helped me solve this problem.
The error I keep getting is:
"expected primary-expression before ',' token"
I have tried both the old syntax for connect
connect(sender, SIGNAL (valueChanged(QString,QString)),
receiver, SLOT (updateValue(QString)) );
and the new syntax (which is shown in the .cpp file below)
connect(sender, &Sender::valueChanged,
receiver, &Receiver::updateValue );
The MainWindow is created in the main.cpp and the 2nd dialog is created on_action_someAction_triggered(), so I know that the instances I am referencing exist. Is there a better way for me to connect the SIGNAL and the SLOT?
Here is the code I am working with (minus the extra unrelated code).
mainwindow .h:
#include <QMainWindow>
#include "shipdia.h"
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
public slots:
void loadSelectedShip(QString shipName);
private slots:
void on_actionNew_Ship_triggered();
private:
Ui::MainWindow *ui;
shipdia *sDialog;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QTextStream>
#include <QObject>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_actionNew_Ship_triggered()
{
sDialog = new shipdia(this);
QObject::connect(&shipdia, //this is were I attempt to
&shipdia::sendShip, //connect the signal/slot
this,&MainWindow::loadSelectedShip); //but always get an error
sDialog ->show();
}
void MainWindow::loadSelectedShip(QString shipName)
{
... do something ... //this code works, but the signal is never received
}
qdialog.h
#ifndef SHIPDIA_H
#define SHIPDIA_H
#include "functions.h"
#include <QDialog>
namespace Ui {
class shipdia;
}
class shipdia : public QDialog
{
Q_OBJECT
public:
explicit shipdia(QWidget *parent = 0);
~shipdia();
private slots:
void on_pushButton_2_clicked();
signals:
void sendShip(QString shipName);
private:
Ui::shipdia *ui;
};
#endif // SHIPDIA_H
qdialog.cpp
#include "shipdia.h"
#include "ui_shipdia.h"
#include <QObject>
#include <QMessageBox>
#include <QTextStream>
#include <QDir>
shipdia::shipdia(QWidget *parent) :
QDialog(parent),
ui(new Ui::shipdia)
{
ui->setupUi(this);
}
shipdia::~shipdia()
{
delete ui;
}
void shipdia::sendSelectedShip(QString shipName)
{
emit sendShip(shipName); //I previously just emitted sendSelectedShip,
//but separating the function did not fix it.
}
void shipdia::on_pushButton_2_clicked()
{
//Code below functions up to next comment
QString shipName = ui->line_23->text();
shipName = QDir::currentPath() + "/shipFolder/" + shipName + ".txt";
QFile shipFile(shipName);
QStringList stringList;
if (shipFile.open(QIODevice::ReadOnly))
{
QTextStream in(&shipFile);
while(!in.atEnd())
{
QString line = in.readLine();
if(line.isNull())
break;
else
stringList.append(line);
}
shipFile.close();
}
//Code above functions ^
sendSelectedShip(shipName); //this line does not produce an error
}

Answer 1

I think, the code should be
sDialog = new shipdia(this);
QObject::connect(sDialog,
&shipdia::sendShip,this,&MainWindow::loadSelectedShip);
and it should be placed in the constructor of the MainWindow, right after ui->setupUi(this); and the on_actionNew_Ship_triggered() function should look like this:
void MainWindow::on_actionNew_Ship_triggered()
{
sDialog ->show();
}
In your original code, a new instance of shipdia will be created everytime the on_actionNew_Ship_triggered() is called. That should be avoided.
Hope this helps.