Quote Originally Posted by weixj2003ld View Post
I define a class A as follows:
Qt Code: 
  1. class A
  2. {
  3.      protected:
  4.      void contentsMousePressEvent (QMouseEvent *e);
  5.      signals:
  6.      void extractClicked();
  7. }
  8. void A::contentsMousePressEvent (QMouseEvent *e)
  9. {
  10.   .....
  11.   emit extractClicked();
  12. }
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when compile,error:error LNK2019: unresolved external symbol ...
means that can not find the function extractClicked.
Why?
Try this:
Qt Code: 
  1. class A:public QWidget
  2. {
  3.  Q_OBJECT
  4.  
  5.      protected:
  6.      void contentsMousePressEvent (QMouseEvent *e);
  7.      signals:
  8.      void extractClicked();
  9. }
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