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();
}