一个类发出一个信号，一个类，用connect连接槽，为啥连不上呢？

[weixin_38087646]

------------------------------------------class winsdkwinsdk::winsdk(){    signaltest();}void winsdk::signaltest(){        qDebug()<<"[3G][winsdk]testing emit signal>>>>>>>";             emit writeDatabaseSignal();        qDebug()<<"[3G][winsdk]testing emit signal>>>>>>>";}------------------------------------------class MainWindowMainWindow::MainWindow{        winsdk *winSDK = new winsdk;        connect(winSDK,SIGNAL(writeDatabaseSignal()),this,SLOT(writeDatabase()));//qDebug  result is true.}void MainWindow::writeDatabase(/*QString string*/){    qDebug()<<"[3G][MainWindow]__WRITEDATABASE__in>>>>>>>>>>>>>>>>>>";}这是怎么回事呢？先谢过了～！～！～！运行结果：[3G][winsdk]testing emit signal>>>>>>> [3G][winsdk]testing emit signal>>>>>>> connect result true