Question

A am trying to make a program that takes a signal from one class and with activation of that signal I want to activate a slot in second class.

In my case the first class is the mainWindow class, this class is subClass of QMainWindow, and in this class is the slot that I want to activate.

This is mainWindow.cpp:

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

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

void mainWindow::slotForStatusBarMessage(QString string)
{
    statusBar()->showMessage(string);
}

The second class is the mainWidget class and it is a subclass of QWidget.

This is mainWidget.cpp:

mainWidget::mainWidget(QWidget *parent) :
    QWidget(parent)
{
    buttonAddNewRecord=new QPushButton("Add new record", this);

    layoutButton=new QHBoxLayout();
    layoutButton->addWidget(buttonAddNewRecord);

    layoutMain=new QVBoxLayout();
    layoutMain->addLayout(layoutButton);

    functionDatabaseOpen();

    setLayout(layoutMain);
}

The signal is emited from functionDatabaseOpen() function:

if (sqlDatabase.open())
{
    emit signalForShowMessageInStatusBar("true");
}
else
{
    emit signalForShowMessageInStatusBar("false");
}

I have made all the settings to the database but i didnt copy here because of space.

I have tried to make connection inside main.cpp but it seems it dosent work.

QObject::connect(mw, SIGNAL(signalForShowMessageInStatusBar(QString)), w, SLOT(slotForStatusBarMessage(QString)));

I cant make this signal/slot connection between classes to work. Can you give me any help.

If you have any question about the code please ask. Sorry for the bad english,I am not a native english speaker.

Thank you very much for your help.

Answer 1

You are emitting the signal from the constructor of mainWidget, and since the connection is only done after you return from that constructor, the signal doesn’t go anywhere.

The easiest fix, not knowing what the rest of the code looks like, would be to move the call to functionDatabaseOpen() in main() after the signal/slot connection is made.