How to deal with signal and slot in different classes in Qt - qt

Question

My UI looks like following diagram:
Inside MainWindow, there is a big red QStackedWidget area where i will use to put different custom stackedwidgets, current StackedWidget1 have three CardWidgets, (StackedWidget and CardWidget are both cpp class), inside each CardWidget, there is a pushbutton, what i want to do is when i click the pushbotton of CardWidget, the CardWidget send signal to MainWindow, the MainWindow then switch from current stackedwidget to another custom stackedwidget, meanwhile, the signal will carry some variables in cardwidget to the new custom stackedwidget.
Now the problem is after i click one pushbutton, the cardwidget1 emit out signal,the slot function in mainwindow didn't react.
I searched out one question similiar to my situation,link, maybe just as Eeli K and dheerendra said, here the cardwidget-sender instance used in connect(...) in mainwindow.cpp is different from the cardwidget-sender instance in StackedWidget1.cpp, so mainwindow actually didn't receive the signal.
Another thing, i construct the cardwidget-sender instance without any argument in mainwindow.cpp, but i construct the cardwidget-sender instance with 5 arguments in StackedWidget1.cpp.
I write a minimal,reproducible example Qt project - download link.
For those who would like to see the code directly, i extract some of its code:
# mainwindow.cpp
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
stackedwidget1 = new StackedWidget1(ui->stackedWidget);
ui->stackedWidget->addWidget(stackedwidget1);
CardWidget* card = new CardWidget();
bool c_res = connect (card, &CardWidget::open_panel_signal, this, &MainWindow::open_panel);
qDebug()<<"Connect open_panels signal and slot ? :"<<c_res;
//If i emit signal from here instead of from cardwidget, it can trigger the slot function, uncomment to see it
// int dummy_int = 0;
// QString dummy_string = "abcd";
// emit card->open_panel_signal(dummy_int, dummy_string);
}
void MainWindow::open_panel(int index, QString text)
{
qDebug()<<"test text from cardwidget"<<index<<"is"<<text;
stackedwidget2 = new StackedWidget2(ui->stackedWidget);
ui->stackedWidget->addWidget(stackedwidget2);
ui->stackedWidget->setCurrentWidget(stackedwidget2);
}
#mainwindow.h
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
public slots:
void open_panel(int index, QString text);
private:
Ui::MainWindow *ui;
StackedWidget1* stackedwidget1;
StackedWidget2* stackedwidget2;
};
# stackedwidget1.cpp
StackedWidget1::StackedWidget1(QWidget *parent) :
QWidget(parent),
ui(new Ui::StackedWidget1)
{
ui->setupUi(this);
for(int col = 0; col< 3; col++){
CardWidget* card = new CardWidget(this,col);
ui->tableWidget->setCellWidget(0, col, card);
ui->tableWidget->update();
}
}
# cardwidget.cpp
CardWidget::CardWidget(QWidget *parent, int index) :
QWidget(parent),
ui(new Ui::CardWidget),
index_(index)
{
ui->setupUi(this);
}
void CardWidget::on_pushButton_clicked()
{
QString text = "text from cardwidget";
emit open_panel_signal(index_, text);
qDebug()<<"emit signal from cardwidget"<<index_;
}
# cardwidget.h
class CardWidget : public QWidget
{
Q_OBJECT
public:
explicit CardWidget(QWidget *parent = nullptr, int index = 0);
~CardWidget();
signals:
void open_panel_signal(int, QString);
private slots:
void on_pushButton_clicked();
private:
Ui::CardWidget *ui;
int index_;
};
# stackedwidget2.cpp
StackedWidget2::StackedWidget2(QWidget *parent) :
QWidget(parent),
ui(new Ui::StackedWidget2)
{
ui->setupUi(this);
}
Is there any good way to solve this problem? Thanks in advance!

Answer 1

The Basic idea should be :
Signal (card Widget) -> Signal (stackedwidget1) -> SLOT(Mainwindow)
You can follow the general approach:
mainwindow.h
public slots:
void open_panel(int, QString);
cardwidget.h
signals:
void open_panel_signal(int, QString);
cardwidget.cpp
void CardWidget::on_pushButton_clicked()
{
QString text = "text from cardwidget";
emit open_panel_signal(index_, text);
qDebug()<<"emit signal from cardwidget"<<index_;
}
stackedwidget1.h
signals:
void open_panel_signal(int, QString);
stackedwidget1.cpp
StackedWidget1::StackedWidget1(QWidget *parent) :
QWidget(parent),
ui(new Ui::StackedWidget1)
{
ui->setupUi(this);
for(int col = 0; col< 3; col++){
CardWidget* card = new CardWidget(this,col);
ui->tableWidget->setCellWidget(0, col, card);
ui->tableWidget->update();
connect(card,SIGNAL(open_panel_signal(int, QString)),this,SIGNAL(open_panel_signal(int, QString)));
}
}
mainwindow.cpp
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
stackedwidget1 = new StackedWidget1(ui->stackedWidget);
ui->stackedWidget->addWidget(stackedwidget1);
connect(stackedwidget1,SIGNAL(open_panel_signal(int, QString)),this,SLOT(open_panel(int, QString)));
}