麻烦大家看看，为什么运行到QDesktopServices:openUrl(url);并没有打开网页？该怎么处理

#include "onlinehelp.h"OnlineHelp::OnlineHelp(QWidget *parent, Qt::WFlags flags)    : QMainWindow(parent, flags){    ui.setupUi(this);    createActions();    createToolBars();}OnlineHelp::~OnlineHelp(){}void OnlineHelp::createActions(){    HelpAction = new QAction(tr("&Help..."), this);    connect(HelpAction, SIGNAL(triggered()), this, SLOT(help()));}void OnlineHelp::createToolBars(){    HelpToolBar = addToolBar(tr("&Help"));    HelpToolBar->addAction(HelpAction);}void OnlineHelp::help(){    QUrl url(directoryof("doc").absoluteFilePath("Google.htm"));     url.setScheme("file");    QDesktopServices::openUrl(url);}QDir OnlineHelp::directoryof(const QString &subdir){    QDir dir(QApplication::applicationDirPath());        #if defined(Q_OS_WIN)    if (dir.dirName().toLower() == "debug"        || dir.dirName().toLower() == "release")                    dir.cdUp();    #elif defined(Q_OS_MAC)    if (dir.dirName() == "MacOS")     {        dir.cdUp();        dir.cdUp();        dir.cdUp();    }    #endif    dir.cd(subdir);    return dir;}