c++ - 使用带有 Q_DECLARE_METATYPE 的默认生成的复制构造函数

Question

假设我有这个自定义类

struct Analytics : public QObject
{
  Q_OBJECT

  public:
  int a  = 12;

  Analytics(const Analytics& a) {
  }

  Analytics(){
  }

};

Q_DECLARE_METATYPE(Analytics)

以上工作正常。但是我必须提供自己的复制构造函数。我尝试使用默认生成的复制构造函数进行此操作，但出现错误

结构分析:公共(public) QObject { Q_OBJECT

  public:
  int a  = 12;

  Analytics(const Analytics& a) = default;

  Analytics(){
  }

};

Q_DECLARE_METATYPE(Analytics)

这是我得到的错误

  5: error: call to implicitly-deleted copy constructor of 'Analytics'
                return new (where) T(*static_cast<const T*>(t));

是否可以将 Q_DECLARE_METATYPE 与默认生成的复制构造函数一起使用。

Answer 1

来自文档:

QObject has neither a copy constructor nor an assignment operator. This is by design. Actually, they are declared, but in a private section with the macro Q_DISABLE_COPY(). In fact, all Qt classes derived from QObject (direct or indirect) use this macro to declare their copy constructor and assignment operator to be private. The reasoning is found in the discussion on Identity vs Value on the Qt Object Model page.

所以你不能复制QObjects和派生自QObject的类。如果您想对 QObjects 使用信号和槽机制，请改用指针。