Qt MainWindow is not updating - multithreading

Question

I am using Qt to generate a Window. Additionally I use libnfc to get access to a nfc reader, so far so good.
In my self written nfc-class i generate a new thread, this thread is polling for new tags on the reader. If there is a new tag, the thread will start a signal event for the MainWindow.
In the main window I have just a QWebView which will show different websites on different states (after start, new tag, tag removed), just realy basic stuff.
My problem is now: that the main window (or the QWebView) is not updating. If i switch to another programm and go back to my app, the window will be updated. I was already searching with google and trying different stuff but nothing helps.
Here the thread code:
class NFC_Thread : public QThread
{
Q_OBJECT
public:
NFC_Thread(NFC_Reader * Reader);
void run();
signals:
void NewTarget(nfc_target Target);
void TargetRemoved(nfc_target Target);
private:
int mError;
bool mStopPolling;
};
void NFC_Thread::run()
{
mError = 0;
mStopPolling = false;
while(!mStopPolling)
{
nfc_target Target;
mError = nfc_initiator_poll_target(mReader->GetDevice(), nmModulations, szModulations, mPollNr, mPollPeriod, &Target);
if(mError > 0)
{
cout << "NFC: found target" << endl;
}
#warning Bug in driver: Timeout generate a NFC_EIO Error, 'https://code.google.com/p/libnfc/issues/detail?id=224'
else if(mError > 0)
{
cout << "NFC: Error" << endl;
mStopPolling = true;
}
else
{
cout << "NFC: no target found" << endl;
}
}
}
MainWindow Code:
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
public slots:
void SetNewTarget(nfc_target Target);
void doTargetRemoved(nfc_target Target);
private:
bool event(QEvent *event);
void resizeEvent(QResizeEvent *);
void adjust();
Ui::MainWindow *ui;
QWebView * mWebView;
};
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
mWebView = new QWebView(this);
mWebView->load(QUrl("http://www.pbuchegger.at/"));
mWebView->show();
}
void MainWindow::SetNewTarget(nfc_target Target)
{
QString str = "NEW TARGET: \n";
{
char * s;
str_nfc_target(&s, Target, false);
str += s;
delete s;
}
//cout << "NFC: Target: " << str << endl;
mWebView->load(QUrl("http://www.google.at"));
update();
repaint();
mWebView->update();
qApp->processEvents();
/*QMessageBox msgBox;
msgBox.setText(str);
msgBox.exec();*/
}
void MainWindow::doTargetRemoved(nfc_target Target)
{
QString str = "TARGET REMOVED: \n";
{
char * s;
str_nfc_target(&s, Target, false);
str += s;
delete s;
}
//cout << "NFC: Target: " << str << endl;
mWebView->load(QUrl("http://www.cde.at"));
update();
repaint();
mWebView->update();
qApp->processEvents();
/*QMessageBox msgBox;
msgBox.setText(str);
msgBox.exec();*/
}
bool MainWindow::event(QEvent *event)
{
if(event->type() == QEvent::Resize)
{
adjust();
return true;
}
return false;
}
void MainWindow::resizeEvent(QResizeEvent *)
{
adjust();
}
void MainWindow::adjust()
{
mWebView->setGeometry(0, 0, ui->centralWidget->geometry().width(), ui->centralWidget->geometry().height());
}
main code:
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
qRegisterMetaType<nfc_target>("nfc_target");
MainWindow w;
w.setWindowState(Qt::WindowMaximized);
NFC_Reader Reader;
nfc_device_string devs;
size_t nr;
QString str = "";
Reader.GetDevices(devs, nr);
if(nr > 0)
{
if(!Reader.InitReader(NULL))
{
str += "Error on init!";
}
else
{
Reader.Start_Polling();
str += "Started Polling!";
}
}
else
{
str += "No Device found!";
}
w.SetText(str);
SignalHelper Helper;
QObject::connect(Reader.GetThread(), SIGNAL(NewTarget(nfc_target)), &Helper, SLOT(doNewTarget(nfc_target)));
QObject::connect(Reader.GetThread(), SIGNAL(TargetRemoved(nfc_target)), &Helper, SLOT(doTargetRemoved(nfc_target)));
QObject::connect(&Helper, SIGNAL(NewTarget(nfc_target)), &w, SLOT(SetNewTarget(nfc_target)));
QObject::connect(&Helper, SIGNAL(TargetRemoved(nfc_target)), &w, SLOT(doTargetRemoved(nfc_target)));
w.show();
int ret = a.exec();
Reader.Abort_Polling();
return ret;
}
As u can see, I have a "Helper" class, this class is just getting the signal in a slot and starting again a signal which will be forward to the mainwindow. If i want to forward the signal directly to the mainwindow, nothing is happening (like the signal is not fired), but i was checking it with the Qt-About box, and the box is showing up.
Helper class:
class SignalHelper : public QObject
{
Q_OBJECT
public slots:
void doNewTarget(nfc_target Target);
void doTargetRemoved(nfc_target Target);
signals:
void NewTarget(nfc_target Target);
void TargetRemoved(nfc_target Target);
};
void SignalHelper::doNewTarget(nfc_target Target)
{
emit NewTarget(Target);
}
void SignalHelper::doTargetRemoved(nfc_target Target)
{
emit TargetRemoved(Target);
}
no compiler errors or linker errors. this code shows just the important stuff, all the unimportant stuff is removed. just for your information the project file:
QT += core gui testlib
QT += webkit
greaterThan(QT_MAJOR_VERSION, 4) {
QT += widgets
}
TARGET = NFC_GUI
TEMPLATE = app
SOURCES += main.cpp \
mainwindow.cpp \
nfc_thread.cpp \
nfc_reader.cpp \
signal_helper.cpp
HEADERS += mainwindow.h nfc_thread.h nfc_reader.h signal_helper.h
FORMS += mainwindow.ui
LIBS += -lnfc

Answer 1

Making my comment an answer:
Your function
bool MainWindow::event(QEvent *event)
{
if(event->type() == QEvent::Resize)
{
adjust();
return true;
}
return false;
}
eats any event which is handled in QMainWindow except for QEvent::Resize. You need to call the default behaviour for events you are not interested in:
bool MainWindow::event(QEvent *event)
{
if(event->type() == QEvent::Resize)
{
adjust();
return true;
}
// call the parent implementation
return QMainWindow::event(event);
}
Note you can also just simply implement QWidget::resizeEvent:
void MainWindow::resizeEvent(QResizeEvent *event)
{
adjust();
QMainWindow::resizeEvent(event);
}

Answer 2

If you're calling slots from signals between different threads, you need to make the connect calls with Qt::QueuedConnection as the Connection Type.