Can't receive signal from MainWindow from QLabel inherited class

Peter_Dev

Hello, everyone!

I'm making a project, where i need to interact with picture. So i inherited class from QLabeland promoted ui->label to it for this purpose. Now i can get mouse click position according to label (I transmit this data via signal to MainWindow). And now comes the problem: I added comboBox touiand i want to send signal of it's item chosen from MainWindow to that inherited class. But when i tried to do that i got SEGFAULT and my program was finished unexpectedly.

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "customlabel.h"
#include <QDebug>
#include <QStandardItemModel>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->label, SIGNAL(MousePressed()), this, SLOT(Mouse_current_pos()));
    connect(ui->comboBox,SIGNAL(activated(int)), this, SLOT(combo_choice(int))); //i think signal being send successfully

    ui->comboBox->addItem("Some menu");
    ui->comboBox->addItem("A");
    ui->comboBox->addItem("B");
    ui->comboBox->addItem("C");
    QStandardItemModel* model =
            qobject_cast<QStandardItemModel*>(ui->comboBox->model());
    QModelIndex firstIndex = model->index(0, ui->comboBox->modelColumn(),
            ui->comboBox->rootModelIndex());
    QStandardItem* firstItem = model->itemFromIndex(firstIndex);
    firstItem->setSelectable(false);
}

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

void MainWindow::Mouse_current_pos()
{
    qDebug() << ui->label->x << " " << ui->label->y;
}

void MainWindow::combo_choice(int argument)
{
    emit combo_box_chosen(argument);
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
private slots:
    void Mouse_current_pos();
    void combo_choice(int);
private:
    Ui::MainWindow *ui;
signals:
    void combo_box_chosen(int);
};
#endif // MAINWINDOW_H

inherited from qlabel class customlabel.cpp

#include "customlabel.h"
#include "mainwindow.h"
#include <QDebug>

CustomLabel::CustomLabel(QWidget *parent) :
    QLabel(parent)
{
    MainWindow a; //im not sure that this is correct. Segfault happens after i added these two lines
    connect(&a, SIGNAL(combo_box_chosen(int)), this, SLOT(process_combo_box(int)));
}

void CustomLabel::mousePressEvent(QMouseEvent *ev)
{
    this->x = ev->x();
    this->y = ev->y();
    emit MousePressed();
}

void CustomLabel::process_combo_box(int argument)
{
    qDebug() << argument;
}

customwidget.h

#ifndef CUSTOMLABEL_H
#define CUSTOMLABEL_H

#include <QWidget>
#include <QLabel>
#include <QMouseEvent>
#include <QDebug>

class CustomLabel : public QLabel
{
    Q_OBJECT
public:
    explicit CustomLabel(QWidget *parent = nullptr);

    void mousePressEvent(QMouseEvent *ev);
    int x,y;
private slots:
    void process_combo_box(int);
signals:
    void MousePressed();
};

#endif // CUSTOMLABEL_H

Any help would be appreciated

Bonnie

Of cource that's not correct :) But I'm not sure what causes the SEGFAULT .
The best way is:
First, make void CustomLabel::process_combo_box(int) public
Then connect it with comboxBox in the MainWindow

    connect(ui->comboBox,SIGNAL(activated(int)), ui->label, SLOT(process_combo_box(int)));

No need to use MainWindow to send the signal.

Peter_Dev

@Bonnie , Perfect! That works! Thank you very much)

Pablo J. Rogina

@Peter_Dev in addition to your issue solved, you may want to use the new syntax for signals & slots, as it provides compile time errors, contrary to runtime warnings with the old syntax you're using.