Qt Application Suspending - qt

Question

How do I detect if my application has been suspended (when someone changes applications) and react by deactivating my timer and then re-activating it when my application becomes un-suspended (when someone re-opens my half running app). Beneath Is how far I have coded so far on this part my app but it gives an error: "'QApplication::QApplication(const QApplication&)' is private" and it says within the context of myapp.cpp line 4. Please if anyone can tell me what I'm doing wrong it would be greatly appreciated.
Here is my code for the main.cpp:
#include <QtGui/QApplication>
#include "qmlapplicationviewer.h"
#include <QObject>
#include <QGraphicsObject>
#include <QTimer>
#include <QVariant>
#include "timecontrol.h"
#include "scorecontrol.h"
#include "Retry.h"
#include <QEvent>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QmlApplicationViewer viewer;
viewer.setOrientation(QmlApplicationViewer::ScreenOrientationLockLandscape);
viewer.setMainQmlFile(QLatin1String("qml/Raker/main.qml"));
viewer.showExpanded();
QObject *rootObject = viewer.rootObject();
QTimer *timmer = new QTimer;
timmer->setInterval(1000);
TimeControl *timcon = new TimeControl;
scorecontrol *scorer = new scorecontrol;
Retry *probeer = new Retry;
QObject::connect(timmer, SIGNAL(timeout()), timcon, SLOT(updateTime()));
QObject::connect(timcon, SIGNAL(setTime(QVariant)), rootObject, SLOT(setTime(QVariant)));
QObject::connect(rootObject, SIGNAL(blockClicked(int, int)), scorer, SLOT(checkRight(int, int)));
QObject::connect(scorer, SIGNAL(setScore(QVariant)), rootObject, SLOT(setScore(QVariant)));
QObject::connect(scorer, SIGNAL(setState(QVariant)), rootObject, SLOT(setState(QVariant)));
QObject::connect(rootObject, SIGNAL(start()), probeer, SLOT(Reetry()));
QObject::connect(probeer, SIGNAL(start()), timmer, SLOT(start()));
QObject::connect(probeer, SIGNAL(start(int)), scorer, SLOT(randomNum(int)));
QObject::connect(probeer, SIGNAL(sReset()), timcon, SLOT(reset()));
QObject::connect(probeer, SIGNAL(tReset()), scorer, SLOT(reset()));
QObject::connect(timcon, SIGNAL(timeOut()), scorer, SLOT(reset()));
QObject::connect(timcon, SIGNAL(setState(QVariant)), rootObject, SLOT(setState(QVariant)));
QObject::connect(timcon, SIGNAL(changeFinal()), scorer, SLOT(changeFinal()));
QObject::connect(scorer, SIGNAL(setFinal(QVariant)), rootObject, SLOT(setFinal(QVariant)));
return app.exec();
}
myApp.h:
#ifndef MYAPP_H
#define MYAPP_H
#include <QApplication>
#include <QObject>
class MyApp : public QApplication
{
public:
MyApp(QApplication &app);
protected:
bool eventFilter(QObject *obj, QEvent *event);
};
#endif // MYAPP_H
myapp.cpp:
#include "myapp.h"
#include <QEvent>
MyApp::MyApp(QApplication &app) : QApplication(app)
{
installEventFilter(this);
}
bool MyApp::eventFilter(QObject *obj, QEvent *event)
{
if (event->type() == QEvent::ApplicationDeactivate)
{
}
if (event->type() == QEvent::ApplicationDeactivate)
{
}
else
{
return false;
}
}

Answer 1

Add an event filter to check for the activate and deactivate events. From the QEvent documentation:
QEvent::ApplicationActivate 121 The application has been made available to the user.
QEvent::ApplicationDeactivate 122 The application has been suspended, and is unavailable to the user.
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),ui(new Ui::MainWindow)
{
ui->setupUi(this);
ui->comboBox->installEventFilter(this);
.
.
.
}
bool MainWindow::eventFilter(QObject *object, QEvent *event)
{
if (event->type() == QEvent::ApplicationDeactivate)
{
// Deactivate timer
}
if (event->type() == QEvent::ApplicationActivate)
{
// Turn timer back on
}
return false;
}

Answer 2

QEvent::AppliciationActivate and QEvent::ApplicationDeactivate have been deprecated (see here). Instead, use QEvent::ApplicationStateChange. There is no need to use an event filter to utilise this; just connect to QGuiApplication::applicationStateChanged(Qt::ApplicationState) and handle it as appropriate.