这是编译时的输出信息
F:\Qt\4.8.4new\bin\moc.exe -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_HAVE_MMX -DQT_HAVE_3DNOW -DQT_HAVE_SSE -DQT_HAVE_MMXEXT -DQT_HAVE_SSE2 -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"f:\Qt\4.8.4new\include\QtCore" -I"f:\Qt\4.8.4new\include\QtNetwork" -I"f:\Qt\4.8.4new\include\QtGui" -I"f:\Qt\4.8.4new\include" -I"f:\Qt\4.8.4new\include\ActiveQt" -I"release" -I"." -I"..\..\Cplus\qtdownloadmanager" -I"." -I"f:\Qt\4.8.4new\mkspecs\win32-g++" -D__GNUC__ -DWIN32 ..\..\Cplus\qtdownloadmanager\widget.h -o release\moc_widget.cppg++ -c -pipe -O2 -frtti -fexceptions -mthreads -Wall -Wextra -DUNICODE -DQT_LARGEFILE_SUPPORT -DQT_DLL -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_HAVE_MMX -DQT_HAVE_3DNOW -DQT_HAVE_SSE -DQT_HAVE_MMXEXT -DQT_HAVE_SSE2 -DQT_THREAD_SUPPORT -DQT_NEEDS_QMAIN -I"f:\Qt\4.8.4new\include\QtCore" -I"f:\Qt\4.8.4new\include\QtNetwork" -I"f:\Qt\4.8.4new\include\QtGui" -I"f:\Qt\4.8.4new\include" -I"f:\Qt\4.8.4new\include\ActiveQt" -I"release" -I"." -I"..\..\Cplus\qtdownloadmanager" -I"." -I"f:\Qt\4.8.4new\mkspecs\win32-g++" -o release\moc_widget.o release\moc_widget.cppg++ -Wl,-s -mthreads -Wl,-subsystem,windows -o release\qtdownloadmanager.exe release/main.o release/widget.o release/moc_widget.o -L"f:\Qt\4.8.4new\lib" -lmingw32 -lqtmain -lQtGui4 -lQtNetwork4 -lQtCore4 mingw32-make[1]: Leaving directory `D:/Documents2/cplus/qtdownloadmanager-build-Desktop-Release'release/moc_widget.o:moc_widget.cpp:(.rdata$_ZTV6Widget[vtable for Widget]+0xbc): undefined reference to `Widget::changeEvent(QEvent*)'collect2: ld returned 1 exit statusmingw32-make[1]: *** [release\qtdownloadmanager.exe] Error 1mingw32-make: *** [release] Error 223:49:59: 进程"C:\MinGw\bin\mingw32-make.exe"退出，退出代码 2 。Error while building/deploying project qtdownloadmanager (target: Desktop)When executing step 'Make'
