我在以下代码中调用RegisterClassEx时收到一个类已存在的错误。此代码在类构造函数中:this->m_wcx.cbSize=sizeof(WNDCLASSEX);//sizeofstructurethis->m_wcx.style=CS_HREDRAW|CS_VREDRAW;//initiallyminimizedthis->m_wcx.lpfnWndProc=&WndProc;//pointstowindowprocedurethis->m_wcx.cbClsExtra=0;//noextraclassmemorythis->m_wcx.cbWndExtra=0;//noe