How to use Signals & Slots

Signals & Slots is a mechanism in Qt for communication between objects. It allows you to connect signals emitted by one object to slots in another object, enabling them to communicate with each other.

Creating Signals

To use Signals & Slots, you first need to create signals in your object. Signals are similar to functions, but they do not have a body and are declared using the signals: keyword.

class MyClass : public QObject
{
  Q_OBJECT
  signals:
    void mySignal();
};

Creating Slots

Slots are functions that can be connected to signals. They are declared using the slots: keyword and can be any normal member function.

class AnotherClass : public QObject
{
  Q_OBJECT
  public slots:
    void mySlot()
    {
      // Do something when the signal is emitted
    }
};

Connecting Signals to Slots

To connect a signal to a slot, you can use the QObject::connect function. When the signal is emitted, the connected slot will be called.

MyClass* obj1 = new MyClass();
AnotherClass* obj2 = new AnotherClass();

QObject::connect(obj1, SIGNAL(mySignal()), obj2, SLOT(mySlot()));

Emitting Signals

To emit a signal, use the emit keyword followed by the signal name and any arguments the signal may have.

class MyClass : public QObject
{
  Q_OBJECT
  signals:
    void mySignal(int value);
};

void MyClass::someFunction()
{
  // Emit the signal with a value
  emit mySignal(42);
}

Conclusion

Signals & Slots is a powerful mechanism in Qt that allows for easy communication between objects. By creating signals in one object and connecting them to slots in another, you can enable seamless communication and interaction between different parts of your application.