Elemental signal and slot example

[Gromenawer]

Hi there. I'm trying to understand the signal and slot mechanism; but I'm afraid that I have no idea of what I'm doing.

I have set up a simple example, that doesn't work, and ends in a "the slot requires more arguments than the signal provide" error. The theoretical behavior is really simple, there is a login screen with a user and password text, and when you click the button, the widget signal those two strings to a controller, and the controller do something with it. In this case, it just show them in the stdout.

Here is all the code I have so far:

controller.h

#ifndef CONTROLLER_H
#define CONTROLLER_H

#include <QObject>
#include <QString>

class Controller : public QObject
{
    Q_OBJECT
public:
    explicit Controller(QObject *parent = 0);

signals:

public slots:
    void doSomething(QString user, QString pass);

};

#endif // CONTROLLER_H

loginScreen.h

#ifndef LOGINSCREEN_H
#define LOGINSCREEN_H

#include <QDialog>

#include "controller.h"

namespace Ui {
class LoginScreen;
}

class LoginScreen : public QDialog
{
    Q_OBJECT

public:
    explicit LoginScreen(QWidget *parent = 0);
    ~LoginScreen();

signals:
    void on_pushButton_clicked();

private:
    Ui::LoginScreen *ui;
};

#endif // LOGINSCREEN_H

controller.cpp

#include "controller.h"

#include <iostream>
#include <QTextStream>

Controller::Controller(QObject *parent) : QObject(parent)
{

}

void Controller::doSomething(QString user, QString pass){

    QTextStream(stdout) << "Doing something..."<<user<<" "<<pass<< endl;

}

loginscreen.cpp

#include "loginscreen.h"
#include "ui_loginscreen.h"

LoginScreen::LoginScreen(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::LoginScreen)
{
    ui->setupUi(this);

}


LoginScreen::~LoginScreen()
{
    delete ui;
}

void LoginScreen::on_pushButton_clicked()
{
    emit (this->ui->userLine->text(),this->ui->passwordLine->text());
}

main.cpp

#include "loginscreen.h"
#include "controller.h"

#include <QApplication>
#include <QObject>


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    Controller mainControl;

    LoginScreen w;


    QObject::connect(&w, &LoginScreen::on_pushButton_clicked,
                     &mainControl, &Controller::doSomething);

    w.show();



    return a.exec();
}

And finally, the loginscreen.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>LoginScreen</class>
 <widget class="QDialog" name="LoginScreen">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>214</width>
    <height>146</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Dialog</string>
  </property>
  <widget class="QLabel" name="statusLabel">
   <property name="geometry">
    <rect>
     <x>10</x>
     <y>10</y>
     <width>47</width>
     <height>13</height>
    </rect>
   </property>
   <property name="text">
    <string>Ready...</string>
   </property>
  </widget>
  <widget class="QLabel" name="userLabel">
   <property name="geometry">
    <rect>
     <x>10</x>
     <y>40</y>
     <width>47</width>
     <height>13</height>
    </rect>
   </property>
   <property name="text">
    <string>User</string>
   </property>
  </widget>
  <widget class="QLabel" name="passwordLabel">
   <property name="geometry">
    <rect>
     <x>10</x>
     <y>70</y>
     <width>47</width>
     <height>13</height>
    </rect>
   </property>
   <property name="text">
    <string>Password</string>
   </property>
  </widget>
  <widget class="QLineEdit" name="userLine">
   <property name="geometry">
    <rect>
     <x>70</x>
     <y>40</y>
     <width>113</width>
     <height>20</height>
    </rect>
   </property>
  </widget>
  <widget class="QLineEdit" name="passwordLine">
   <property name="geometry">
    <rect>
     <x>70</x>
     <y>70</y>
     <width>113</width>
     <height>20</height>
    </rect>
   </property>
  </widget>
  <widget class="QPushButton" name="pushButton">
   <property name="geometry">
    <rect>
     <x>70</x>
     <y>110</y>
     <width>75</width>
     <height>23</height>
    </rect>
   </property>
   <property name="text">
    <string>Login</string>
   </property>
  </widget>
 </widget>
 <resources/>
 <connections/>
</ui>

So the question would be, what would be the correct "connect" function? I have read, watch and follow different tutorials and documentations and I'm still really confuse on how are those two arguments suppose to pass from one place to the other.

[mrjj]

hi and welcome
The reason the connect dont like you is because
doSomething has parameters and
on_pushButton_clicked dont.

You just just need to define a new signal in LoginScreen ( like the slot)
public signals:
void doSomething(QString user, QString pass);

then in on_pushButton_clicked(); ( which is called when u click button)
u emit this signal
emit doSomething (this->ui->userLine->text(),this->ui->passwordLine->text());

and from outside u have connect the 2 "doSomething "

so in short, the button clicked is hooked to local slot.
The local slot will then emit your signal with parameters.
From outside, this signal is connected to a slot with same signature. ( same params)

Hope I explained it good enough.

[Gromenawer]

TEMP_EDIT: How do I mark the post as solved??

Thank you! ; it took me a little bit but I got it. I'm leaving here the final code in case someone need it:

controller.h stays the same.
controller.cpp stays the same.

#ifndef LOGINSCREEN_H
#define LOGINSCREEN_H

#include <QDialog>

#include "controller.h"

namespace Ui {
class LoginScreen;
}

class LoginScreen : public QDialog
{
    Q_OBJECT

public:
    explicit LoginScreen(QWidget *parent = 0);
    ~LoginScreen();

signals:
    void doSomething(QString user, QString pass);

public slots:
    void on_pushButton_clicked();

private:
    Ui::LoginScreen *ui;
};

#endif // LOGINSCREEN_H

loginScreen.cpp

#include "loginscreen.h"
#include "ui_loginscreen.h"

LoginScreen::LoginScreen(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::LoginScreen)
{
    ui->setupUi(this);

}


LoginScreen::~LoginScreen()
{
    delete ui;
}

void LoginScreen::on_pushButton_clicked()
{
    emit doSomething(this->ui->userLine->text(),this->ui->passwordLine->text());
}

main.cpp

#include "loginscreen.h"
#include "controller.h"

#include <QApplication>
#include <QObject>


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    Controller mainControl;

    LoginScreen w;

    QObject::connect(&w, &LoginScreen::doSomething,
                     &mainControl, &Controller::doSomething);

    w.show();



    return a.exec();
}