在继承自 QObject 的类中使用信号

Question

我问是否有办法在继承自 QObject 的类中使用 signals，如下所示：

mysuperclass.cpp

#include "mysuperclass.h"

MySuperclass::MySuperclass(quint16 port, QObject *parent) :
  QObject(parent), port(port)
{
  this->connected = false;
}

mysuperclass.h

#include <QAbstractSocket>

class MySuperclass: public QObject
{
  Q_OBJECT
public:
  explicit MySuperclass(quint16 port = 0, QObject *parent = 0);

signals:
   //there is nothing here
public slots:
  virtual void newValue(){qDebug() << "newValue";}
  virtual void connectionEstablished(){qDebug() << "connectionEstablished";}
  virtual void disconnected(){qDebug() << "disconnected";}
protected:
  QAbstractSocket* networkSocket;
  quint16 port;
  bool connected;
};

我的子类.cpp

#include <QTcpSocket>
#include <QHostAddress>

MySubClass::MySubClass(quint16 ServerPort, QObject *parent) : 
  MySuperClass(ServerPort, parent) 
{
  this->networkSocket = new QTcpSocket(this);
  ...
  connect(this->networkSocket, SIGNAL(connected()),this,
    SLOT(connectionEstablished()));
  connect(this->networkSocket, SIGNAL(disconnected()),this,
    SLOT(disconnected()));
  connect(this->networkSocket, SIGNAL(readyRead()),this, SLOT(newValue()));
}

mysubclass.h

#include <QObject>
#include "mysuperclass.h"

class MySubClass: public MySuperClass
{
 public:
   MySubClass(quint16 ServerPort, QObject* parent=0);

 public slots:
   void newValue();
   void connectionEstablished();
   void disconnected();
};

Answer 1

您也必须在派生类中包含Q_OBJECT 宏（但不要再次从QObject 派生）。仅当派生类声明信号或槽时，宏才是必需的。发送父信号或连接父槽是没有必要的（这也意味着不需要重新定义已经存在的信号或槽）。

来自Qt's documentation：

Q_OBJECT 宏必须出现在声明自己的信号和槽或使用 Qt 元对象系统提供的其他服务的类定义的私有部分中。

示例

class MySubClass : public MySuperClass {
  Q_OBJECT

  public:
    MySubClass(quint16 ServerPort, QObject* parent=0);

  public slots:
    void newValue();
    void connectionEstablished();
    void disconnected();
};

另一方面，如果你想连接到父类中的一个插槽，但在派生类中实现它，那么你必须将其设为虚拟：

class MySuperclass : public QObject {
  Q_OBJECT
  // ...
public slots:
  virtual void newValue(); // can be virtual pure also
};

class MySubClass : public MySuperClass {
public:
  virtual void newValue() override; // overrides parent's
}

请注意，派生类中无需使用Q_OBJECT 宏，也无需使用slot: 标签。插槽毕竟是正常的方法。当然，如果你添加新的槽或信号，你必须使用它。