Qt progressBar获取Unhandled异常如何检测父窗口小部件何时完成加载

Question

im using Qt QProgressBar and place it in the statusBar on my main window Like this in the constructor :

pb = new QProgressBar(statusBar());
pb->setTextVisible(false);
pb->hide();
statusBar()->addPermanentWidget(pb);

then im running procsses (web page loadding in this case ) and trying to show the progress with :

connect(ui.webView, SIGNAL(loadProgress(int)), SLOT(setProgress (int)));
void myMainWindow:: setProgress(int progress)
{
pb->show();
pb->setRange(0,100);
pb->setValue(progress);
}

But im getting Unhandled exception when it comes to pb->show() I guess it has to do something with loading the parent main windows and then the progress bar I was reading about the QAbstractEventDispatcher and processEvents but not understood how to implement it .

i did small test and put the pb->show() function call in button click signal/slut that means im triggering the pb->show() after the web page and the mainwindows fully loaded and its working fine without the exception. that make me belive there is problem with the event processing.

here is the class :

class MainWindowMainWindowContainer : public QMainWindow 
{
    Q_OBJECT

public:
    MainWindowContainer(QWidget *parent = 0);

 public slots:

    void adjustLocation();
    void changeLocation();
    void adjustTitle();
    void setProgress(int p);
    void finishLoading(bool);
    void finishedSlot(QNetworkReply* reply);


private:
    Ui::OnLineBack_mainWindow ui;    
    int progress;

    void createWebViewActions();
    QProgressBar *pb;
    void setprogressBar(int progress,bool show);

 };

MainWindowContainer::MainWindowContainer(QWidget* parent) : 
    QMainWindow(parent),

{
 ui.setupUi(this);
 progress = 0;


createWebViewActions();
ui.webView->load(QUrl("www.cnnnn.com"));
ui.webView->show();

pb = new QProgressBar(statusBar());
pb->setTextVisible(false);
pb->hide();
statusBar()->addPermanentWidget(pb);
}
 void MainWindowContainer::createWebViewActions()
{
    connect(ui.webView, SIGNAL(loadFinished(bool)), SLOT(adjustLocation()));
    connect(ui.webView, SIGNAL(titleChanged(QString)), SLOT(adjustTitle()));
    connect(ui.webView, SIGNAL(loadProgress(int)), SLOT(setProgress(int)));
    connect(ui.webView, SIGNAL(loadFinished(bool)), SLOT(finishLoading(bool)));
    connect(ui.webView, SIGNAL(linkClicked(const QUrl&)),this, SLOT(linkClicked(const QUrl&)));

}
void MainWindowContainer::setProgress(int p)
{
    progress = p;
    adjustTitle();
}
 void MainWindowContainer::adjustTitle()
{
    qApp->processEvents(); 

    pb->show();
    if (progress <= 0 || progress >= 100)
    {
        QString titl =  ui.webView->title();
        statusBar()->showMessage(titl);
        setprogressBar(-1,false);

    }
    else
    {

        statusBar()->showMessage(QString("%1 (%2%)").arg(ui.webView->title()).arg(progress));
        setprogressBar(progress,true);
    }
}

 void MainWindowContainer::finishLoading(bool)
{   
    progress = 100;
    adjustTitle();

}
 void MainWindowContainer::setprogressBar(int progress,bool show)
{
     if(show)
    {
        pb->show();
        pb->setRange(0,100);
        pb->setValue(progress);
    }
    else
    {
        pb->hide();
    } 
}

Answer 1

In your createWebViewActions() function you connect the signals to their respective slots. (One small remark, the connect for the titleChanged(QString) signal and adjustTitle() slot fails because they have different signatures)

Among others you are connecting the signal loadProgress(int) to slot setProgress(int) . In this slot you call adjustTitle() where the instruction pb->show() is being executed.

Notice that you are calling the createWebViewActions() function before the call to QProgressBar constructor

(...)
createWebViewActions();  <------ here you establish the signal->slot connections
ui.webView->load(QUrl("www.cnnnn.com"));
ui.webView->show();

pb = new QProgressBar(statusBar()); <------ here you call the QProgressBar constructor
pb->setTextVisible(false);
pb->hide();
statusBar()->addPermanentWidget(pb);
(...)

I think that maybe this slot (setProgress()) is being called before the QProgressBar is constructed which triggers the Unhandled exception you are getting.

You could try and move the call to the QProgressBar constructor so that it is created before the slots connection.