Error while connecting QPushButton::clicked signal to a slot

Question

First of all, I created about 20 push buttons using for loop. And named them using if else loop. Now, I want to connect each push buttons with the new dialog box. If I had used the design mode of QT, it would show me the name of the button when I press connect(ui->pushButton_0, SIGNAl(released()), SLOT(digit_pressed()) something like this. But, I don't know the name of the pushbutton I made as the for and if else loop made it. The connect(ui-> .......) also doesn't show any predictions. How can I link these push buttons and a new dialog box?

Here is my code:

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;

private slots:
    void on_pushButton_clicked();

};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QPushButton>
#include <QVBoxLayout>
#include "amputation.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->)



    QPixmap pix("/home/skanda/Desktop/D4564.png");
    ui->label_2->setPixmap(pix);
    setWindowTitle("First Aid");

    QVBoxLayout *lay = new QVBoxLayout();
    int i;
    for(i=0;i<25;i++)
    {
        if(i==0){
             QPushButton *button = new QPushButton("Amputation");
             lay->addWidget(button);
        }
        else if(i==1){
            QPushButton *button = new QPushButton("Asthama");
            lay->addWidget(button);

        }
        else if(i==2){
            QPushButton *button = new QPushButton("Bleeding");
            lay->addWidget(button);

        }
        else if(i==3){
            QPushButton *button = new QPushButton("Burns");
            lay->addWidget(button);

        }
        else if(i==4){
            QPushButton *button = new QPushButton("Chest Pain");
            lay->addWidget(button);

        }
        else if(i==5){
            QPushButton *button = new QPushButton("Diarrhoea");
            lay->addWidget(button);

        }
        else if(i==6){
            QPushButton *button = new QPushButton("Drowning");
            lay->addWidget(button);

        }
        else if(i==7){
            QPushButton *button = new QPushButton("Epilepsy");
            lay->addWidget(button);

        }
        else if(i==8){
            QPushButton *button = new QPushButton("Fainting");
            lay->addWidget(button);

        }
        else if(i==9){
            QPushButton *button = new QPushButton("Fever");
            lay->addWidget(button);

        }
        else if(i==10){
            QPushButton *button = new QPushButton("Food Poisoning");
            lay->addWidget(button);

        }
        else if(i==11){
            QPushButton *button = new QPushButton("Fracture");
            lay->addWidget(button);

        }
        else if(i==12){
            QPushButton *button = new QPushButton("Head Injury");
            lay->addWidget(button);

        }
        else if(i==13){
            QPushButton *button = new QPushButton("Muscle Strain");
            lay->addWidget(button);

        }
        else if(i==14){
            QPushButton *button = new QPushButton("No breathing");
            lay->addWidget(button);

        }
        else if(i==15){
            QPushButton *button = new QPushButton("Nose bleed");
            lay->addWidget(button);

        }
        else if(i==16){
            QPushButton *button = new QPushButton("Poisoning");
            lay->addWidget(button);

        }
        else if(i==17){
            QPushButton *button = new QPushButton("Snake Bites");
            lay->addWidget(button);

        }
        else if(i==18){
            QPushButton *button = new QPushButton("Stroke");
            lay->addWidget(button);

        }
        else if(i==19) {
            QPushButton *button = new QPushButton("Sun Burn");
            lay->addWidget(button);

        }
        else if(i==20) {
            QPushButton *button = new QPushButton("Testicle Pain");
            lay->addWidget(button);

        }
        else if(i==21) {
            QPushButton *button = new QPushButton("Ulcer");
            lay->addWidget(button);

        }
        else if(i==22) {
            QPushButton *button = new QPushButton("Child delievery");
            lay->addWidget(button);

        }
        else if(i==23) {
            QPushButton *button = new QPushButton("Heart Attack");
            lay->addWidget(button);

        }
        else {
            QPushButton *button = new QPushButton("Gastric");
            lay->addWidget(button);

        }
    }


    ui->scrollContents->setLayout(lay);
}

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

void MainWindow::on_pushButton_clicked(){
    Amputation amp;
    amp.setModal(true);
    amp.show();
}

**In these codes, I have tried my luck by creating on_pushButton_clicked() function. But, it was just a try. **

Answer 1

As in programming everything is cooking, :), let's see what are the ingredients of connect() :

connect(sender, &Sender::signal, receiver, &Receiver::slot);

so sender would be the buttons , the signal is the clicked , the receiver itself, that is, this , and the slot on_pushButton_clicked

I see unnecessary if-else, everything can be reduced to a for:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QPushButton>
#include <QVBoxLayout>
#include "amputation.h"

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


    QPixmap pix("/home/skanda/Desktop/D4564.png");
    ui->label_2->setPixmap(pix);
    setWindowTitle("First Aid");

    QVBoxLayout *lay = new QVBoxLayout();
    QStringList names{"Amputation", "Asthama", "Bleeding", "Burns", "Chest Pain",
                      "Drowning", "Diarrhoea", "Epilepsy", "Fainting", "Fever",
                      "Food Poisoning", "Fracture", "Head Injury", "Muscle Strain",
                     "No breathing", "Nose bleed", "Poisoning", "Snake Bites",
                      "Stroke","Sun Burn", "Testicle Pain", "Ulcer", "Child delievery",
                      "Heart Attack", "Gastric"};
    for(const QString & name: names)
    {
        QPushButton *button = new QPushButton(name);
        lay->addWidget(button);
        connect(button, &QPushButton::clicked, this, &MainWindow::on_pushButton_clicked)

    }
    ui->scrollContents->setLayout(lay);
}

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

void MainWindow::on_pushButton_clicked(){
    Amputation amp;
    amp.setModal(true);
    amp.show();
}

Note:

avoid using the old style of connection, has many disadvantages, read the content of the following link for more information:

• https://wiki.qt.io/New_Signal_Slot_Syntax

Answer 2

1. Make all these QPushButton members of a class such that they are created and destroyed properly rather than creating them in an loop.

2. Once you have each one as a separate member, then have a method InitializeConnections() and make all the connections under it using the Qt connect syntax.

If you believe these buttons are part of the MainWindow class, then your class can look something like this :

class MainWindow{
    ...
    ...
    private :
      // Will make connections of each button to it's respective slot.
      void InitializeConnections();

    private :
      QPushButton *mAmputationButton;
      QPushButton *mAsthmaButton;
    //.. so on
};

And in MainWindow.cpp :

#include <QPushButton>
#include <QVBoxLayout>

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow),
mAmputationButton(new QPushButton("Amputation") ),
mAsthmaButton(new QPushButton("Asthama") )
{
   InitializeConnections();
}

void MainWindow::InitializeConnections()
{
   connect(mAmputationButton, &QPushButton::clicked, this, &MainWindow::amputation_slot );
   connect(mAsthmaButton, &QPushButton::clicked, this, &MainWindow::asthma_slot );
  // same way for others.
}

The slots that i have mentioned are just for example, connect it to the slot that you need it to be connected to.

UPDATE :

Here is a mini-implementation made using just the two buttons :

MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
   
class QPushButton;

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    QPushButton *mAmputationButton;
    QPushButton *mAsthmaButton;

private slots:
    void on_pushButton_clicked();

};

MainWindow.cpp

#include "MainWindow.h"
#include <QPushButton>
#include <QVBoxLayout>
#include <QDialog>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    mAmputationButton( new QPushButton("Amputation" ) ),
    mAsthmaButton( new QPushButton("Astham" ) )
{
    setWindowTitle("First Aid");

    QWidget *sampleWidget = new QWidget();
    QVBoxLayout *lay = new QVBoxLayout();
    lay->addWidget(mAmputationButton);
    connect(mAmputationButton, &QPushButton::clicked, this, &MainWindow::on_pushButton_clicked );
    connect(mAsthmaButton, &QPushButton::clicked, this, &MainWindow::on_pushButton_clicked );
    lay->addWidget(mAsthmaButton);
    sampleWidget->setLayout(lay);
    setCentralWidget(sampleWidget);
}

MainWindow::~MainWindow(){}

void MainWindow::on_pushButton_clicked(){
    QDialog *sampleDialog = new QDialog();
    sampleDialog->setModal(true);
    sampleDialog->show();
}

Note1 : In the slot on_pushbutton_clicked , I am just creating a new dialog and showing it. Just add your slot logic there and you will be good to go.

Note2 : It will be advisable to have all your connections in a single method such as Initialize Connections as already mentioned above.

Take this mini-implementation just as an example that you can work on top of rather than a copy-paste use of it.