error LNK2001: unresolved external symbol "public: virtual struct QMetaObject const （转）

The form that uses slots/signals needs to have the Q_OBJECT, the other form doesnt. Removing the Q_OBJECT on the form that doesnt need the slots/signals results in an dll that does in fact link.

The Q_OBJECT macro at the beginning of the class definition is necessary for all classes that define signals or slots

只有加入了Q_OBJECT，你才能使用QT中的signal和slot机制。
比如编写事件接口等程序时，有时会出现如下问题：
在PC端成功编译，但在开发板端却显示错误：
QObject::connect: No such slot QWidget::*******()
QObject::connect: (sender name: 'unnamed')
QObject::connect: (receiver name: 'unnamed')

这时候，就必须在头文件派生类的时候，首先像下面那样引入Q_OBJECT宏：
class MyMainWindow : public QWidget
{
Q_OBJECT
......
}

（摘自：http://www.qtforum.org/article/17828/linker-problem-error-lnk2001.html和http://blog.chinaunix.net/u2/67519/showart_677875.html）