Signal/slot connection doesn't work.

[Demorald]

I launch a Colours class window through my main.cpp:

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

  QApplication app(argc, argv);

  Colours window;

  window.resize(500, 500);
  window.setWindowTitle("Colours");
  window.show();


  return app.exec();
}

This window does some work, drawing shapes etc.

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

Colours::~Colours()
{
    delete ui;
}
void Colours::paintEvent(QPaintEvent *e) {

  Q_UNUSED(e);

  doPainting();

}

class MyButton : public QWidget {

 public:
     MyButton(QWidget *parent = 0);
};

MyButton::MyButton(QWidget *parent)
    : QWidget(parent) {

  QPushButton *quitBtn = new QPushButton("Quit", this);
  quitBtn->setGeometry(200, 40, 75, 30);

  connect(quitBtn, &QPushButton::clicked, qApp, &QApplication::quit);
}



void Colours::doPainting() {

  QPainter painter(this);

  painter.setRenderHint(QPainter::Antialiasing);
  painter.setPen(QColor("#d4d4d4"));

  painter.setBrush(QBrush("#8B4513"));
  painter.drawRect(100, 150, 300, 300);



  painter.setBrush(QBrush("#D2691E"));
  painter.drawChord(100, 50, 300, 200, 0, 16*180);

  painter.setBrush(QBrush("#A0522D"));
  painter.drawRect(200, 350, 100, 100);

  painter.setBrush(QBrush("#8B4513"));
  painter.drawRect(280, 400, 10, 10);


  QBrush tb(Qt::transparent);
  ui->Button->setPalette(QPalette(tb, tb, tb, tb, tb, tb, tb, tb, tb));
  ui->Button->setFlat(true);

  QFont f("Arial", 15, QFont::Bold);
  ui->lineEdit->setFont(f);

void Colours::on_Button_clicked()
{
    QMessageBox::about(this, "Header", "Information");
}


}

But when it comes to using a colours.ui form, nothing works: I create a button in it, go to slot, and regardless of what i type there, nothing happens. Initially i wanted to draw some other shapes using this button, but even that QMessageBox thing there just does not work. I just press the button and nothing happens.

Any thoughts what causes it?

colours.h:

#ifndef COLOURS_H
#define COLOURS_H

#include <QWidget>
#include <QDialog>
#include <QMainWindow>
#include "ui_mainwindow.h"

namespace Ui {
class Colours;
}

class Colours : public QDialog {

  public:
    Colours(QWidget *parent = 0);
    ~Colours();

  protected:
    void paintEvent(QPaintEvent *e);

private slots:
    void on_pushButton_clicked();

    void on_Button_clicked();

    void on_save_clicked();

private:
    void doPainting();
     Ui::Colours *ui;
};
#endif // COLOURS_H

[VintoreZZ]

Aren't you missing Q_OBJECT macro? It is neccessary to make signals/slots work.

class Colours : public QDialog {
Q_OBJECT //This is missing
  public:
    Colours(QWidget *parent = 0);
    ~Colours();

  protected:
    void paintEvent(QPaintEvent *e);

private slots:
    void on_pushButton_clicked();

    void on_Button_clicked();

    void on_save_clicked();

private:
    void doPainting();
     Ui::Colours *ui;
};
#endif // COLOURS_H

After adding the macro, run qmake (right click on your project -> run qmake)

[Christian Ehrlicher]

@Demorald said in Signal/slot connection doesn't work.:

MyButton::MyButton(QWidget *parent)
: QWidget(parent) {

QPushButton *quitBtn = new QPushButton("Quit", this);
quitBtn->setGeometry(200, 40, 75, 30);

connect(quitBtn, &QPushButton::clicked, qApp, &QApplication::quit);
}

What do you try to achieve with this? And even if this is not really importat - where do you instantiate it so you can click on this button?

[AnneRanch]

1. Verify "connect"
   if (connect(.....) )
   ......

2. Verify "button pushed " - change the function to return value and check for it - in pseudo code or do simple print to validate the function is executed.

   int on_button_pushed ()
   .{
   print " on_button_pushed " executing...

   and / or

   return 0; // success
   }

if(on_button_pushed())
print OK
else
print failed

You can do simple - limited to "standard" methods - signal / slot design in QtDesigner - "Edit signal / slot" . The "connect" is done using "drag and drop".
The "problem" is - you do not have way to check the build code - it needs to be "function" verified.

[JonB]

@AnneRanch
If you are doing return 0; // success you won't want if(on_button_pushed()) print OK as that will give the opposite result from intended. Better make it bool TheClass::on_button_pushed () and have it return true on success. But if on_button_pushed () is a slot which you connect() to a signal you can't check the return value anyway (though of course you can still put qDebug()/print statements inside it if you wish).

[AnneRanch]

Sorry , I did not pay attention - the decisions were reversed.
However, I have a "natural" aversion against using #define(d) bool , true etc.
I do understand that endless discussions about what is " true " zero or anything else have been conducted and do not wish to start another one here.

But I hope my (main) point of checking functions returns as an aid in debugging has been understood by the original poster.

Cheers