Passing Variable between 2 Forms QT - c++

Question

i'm a beginner so if it possible explain to me how to pass variable between 2 forms for example:
i have the first Form called : Send.ui - send.cpp - send.h
and the second form called : Receive.ui - receive.cpp - receive.h
we gonna suppose that i have a variable called age=25 in Send.cpp and a push button
i want that when i press the push button he will open the second form Receive.ui and i will have a variable in this second form age=25
that's meen if i change the variable in the Send.cpp he will be automatically changed in Receive.cpp
and thanks in advence

Answer 1

For communication between objects, Qt has a mechanism called Signals and Slots.
Here is a example of how you can use signals and slots:
In this example I will use spinboxes to visually represent the variable(age) that you mentioned.
1. Open Receive form
In Send, create the button that will open the receive form.
send.h
public:
QPushButton *pushButton;
send.cpp
pushButton = ui->pushButtonSend;
Now create a slot in mainwindow to show receive form.
mainwindow.cpp
void MainWindow::showReceiveForm()
{
receiveForm->show();
}
mainwindow.h
private slots:
void showReceiveForm();
Now connect clicked signal from the push button to the slot in mainwindow.cpp. This will call the slot function everytime the button is clicked.
connect(sendForm->pushButton,SIGNAL(clicked()),this,SLOT(showReceiveForm()));
2. Send Age value
To send the age value to receive form, whenever it's value is changed in send form, connect the valueChanged signal from the QSpinBox in send form to a slot in receive form.
send.h:
public:
QSpinBox *spinBox;
send.cpp
spinBox = ui->spinBoxSend;
Slot in receive.cpp:
void Receive::receiveAge(int age)
{
ui->spinBoxReceive->setValue(age);
}
Now connect signal and slot in mainwindow.cpp.
connect(sendForm->spinBox,SIGNAL(valueChanged(int)),receiveForm,SLOT(receiveAge(int)));
In this example, I used predefined signals from QPushButton and QSpinBox, but you can create your own signals and emit them whenever.
Define custom signals in the header files:
signals:
void exampleSignal(int someArgument);
And emit them with the "emit" keyword.
emit exampleSignal(somenumber);