I have following main.cpp:
#include <QtQml>
#include <QApplication>
#include <QQmlApplicationEngine>
#include "database/uepeoplemodel.h"
#include "core/uestatus.h"
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
UeStatus* ueApplicationStatus=new UeStatus(qApp);
UePeopleModel* uePeopleModel=new UePeopleModel(qApp);
QObject::connect(uePeopleModel,
SIGNAL(ueSignalDatabaseConnectionChanged(UeTypeDatabaseConnectionStatus)),
ueApplicationStatus,
SLOT(ueSignalDatabaseConnectionChanged(UeTypeDatabaseConnectionStatus)));
engine.rootContext()->setContextProperty("uePeopleModel",
uePeopleModel);
engine.rootContext()->setContextProperty("ueApplicationStatus",
ueApplicationStatus);
engine.addImageProvider(QLatin1String("uePeopleModel"),
uePeopleModel);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}
Now, inside main.cpp I create two objects from classes:
UeStatus* ueApplicationStatus=new UeStatus(qApp);
UePeopleModel* uePeopleModel=new UePeopleModel(qApp);
and I connect signal from UePeopleModel to slot in ueApplicationStatus:
QObject::connect(uePeopleModel,
SIGNAL(ueSignalDatabaseConnectionChanged(UeTypeDatabaseConnectionStatus)),
ueApplicationStatus,
SLOT(ueSignalDatabaseConnectionChanged(UeTypeDatabaseConnectionStatus)));
The problem is when uePeopleModel is created, the signal is emmited inside constructor:
UePeopleModel::UePeopleModel(QObject* parent)
: QSqlQueryModel(parent),
QQuickImageProvider(QQmlImageProviderBase::Image,
QQmlImageProviderBase::ForceAsynchronousImageLoading)
{
if(!QSqlDatabase::connectionNames().contains(UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE,
Qt::CaseInsensitive))
{
this->ueSetDatabase(QSqlDatabase::addDatabase(UePosDatabase::DATABASE_DRIVER,
UePosDatabase::UeDatabaseConnectionNames::DATABASE_CONNECTION_NAME_PEOPLE));
} // if
this->ueDatabase().setHostName(/*this->uePosSettings()->ueDbHostname()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_HOSTNAME);
this->ueDatabase().setDatabaseName(/*this->uePosSettings()->ueDbName()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_NAME);
this->ueDatabase().setUserName(/*this->uePosSettings()->ueDbUser()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_USERNAME);
this->ueDatabase().setPassword(/*this->uePosSettings()->ueDbPassword()*/UePosDatabase::UeDatabaseConnectionParameters::DATABASE_PASSWORD);
if(this->ueDatabase().open())
{
emit this->ueSignalDatabaseConnectionChanged(CONNECTED);
this->setQuery(UePosDatabase::UeSqlQueries::UeTablePeople::SQL_QUERY_GET_ALL_PEOPLE,
this->ueDatabase());
/*
if(this->lastError().isValid())
qDebug() << this->lastError();
*/
}
else
{
emit this->ueSignalDatabaseConnectionChanged(NOT_CONNECTED);
// qDebug() << this->ueDatabase().lastError();
}
// qDebug() << this->ueDatabase().connectionNames();
} // default constructor
before connect is issued and therfore ueApplicationStatus object does not catch is with slot. Does anyone has idea how to get rid of this situation?
You shouldn't use the constructor to open the connection with the database.
Use the constructor only to instantiate other classes, initialize variables, allocate memory and so on.
In your case, your constructor should be used to initialize the database, but you could create another method with:
if(this->ueDatabase().open())
{
emit this->ueSignalDatabaseConnectionChanged(CONNECTED);
this->setQuery(UePosDatabase::UeSqlQueries::UeTablePeople::SQL_QUERY_GET_ALL_PEOPLE,
this->ueDatabase());
}
else
{
emit this->ueSignalDatabaseConnectionChanged(NOT_CONNECTED);
}
This method would be called after the connect you have in your main.cpp.
I've solved the problem by adding method void ueConnectToDatabase() and moved the content of constructor into it and redefined main.cpp as:
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
UeStatus* ueApplicationStatus=new UeStatus(qApp);
UePeopleModel* uePeopleModel=new UePeopleModel(qApp);
QObject::connect(uePeopleModel,
SIGNAL(ueSignalDatabaseConnectionChanged(UeTypeDatabaseConnectionStatus)),
ueApplicationStatus,
SLOT(ueSignalDatabaseConnectionChanged(UeTypeDatabaseConnectionStatus)));
uePeopleModel->ueConnectToDatabase();
engine.rootContext()->setContextProperty("uePeopleModel",
uePeopleModel);
engine.rootContext()->setContextProperty("ueApplicationStatus",
ueApplicationStatus);
engine.addImageProvider(QLatin1String("uePeopleModel"),
uePeopleModel);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}
Now the object is created, signal and slot connected and AFTER this the connection to database occurs.
Related
Whenever the application window is minimized or maximized i want to link that signal with a function.
This is the code.
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w(model ); // This is QWidget
w.show();
QObject::connect(&w, &QWindow::windowStateChanged, [&](Qt::WindowState state) {
});
// how will i define the QObject::connect
return application.exec();
}
What would be the parameters for the QObject::connect function ?
You cannot use the connect function to connect to different slots based on the given value. You can however simply call the functions based on the value by checking the value in your lambda.
At least, you could if you had the signal. However, your connect suggests that w is - or inherits - a QWindow. You can obviously only connect to signals your class provides. As your Renderer is a QWidget, you have to check that class.
The documentation of QWidget tells us, that there is no windowStateChanged signal, but it states:
When the window state changes, the widget receives a changeEvent() of type QEvent::WindowStateChange.
So therefor we can create our own signal and connect to that. This can look similar to the following working example:
#ifndef RENDERER_H
#define RENDERER_H
#include <QWidget>
#include <QEvent>
class Renderer : public QWidget {
Q_OBJECT
signals:
void stateChanged(bool isMaximized);
protected:
void changeEvent(QEvent *e)
{
if(e->type() == QEvent::WindowStateChange) {
emit stateChanged(windowState() & ~Qt::WindowMaximized);
}
QWidget::changeEvent(e);
}
};
#endif // RENDERER_H
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w; // This is QWidget
w.show();
QObject::connect(&w, &Renderer::stateChanged, [&](bool maximized) {
qDebug() << "Maximized?" << maximized;
});
return application.exec();
}
I was able to solve by using QApplication::focusWindow()
int main(int argc, char *argv[])
{
QApplication application(argc, argv);
Renderer w; // This is QWidget
w.show();
QObject::connect(QApplication::focusWindow(), &Renderer::stateChanged, [&](bool maximized) {
qDebug() << "Maximized?" << maximized;
});
return application.exec();
}
The problem I have in my code is, once the QML engine uplouded the QProcess stop!! Is it possible to let QProcess run while the QMLis already in operation!
the idea is: I want the user to be able to interact with only one specific mouse and one keyboard and to continually check this condition!
Can some one check what is the problem here?
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
bool scanForDevices=0;
USBdeviceID *usbdeviceid =new USBdeviceID();
engine.rootContext()->setContextProperty("USBdeviceID", usbdeviceid);
QProcess OProcess;
QString Command; //Contains the command to be execute
Command = "lsusb";
while (1)
{
OProcess.start(Command,QIODevice::ReadOnly); //Starts execution of command
OProcess.waitForFinished(); //Waits for execution to complete
QString StdOut = OProcess.readAllStandardOutput(); //Reads standard output
QString StdError = OProcess.readAllStandardError(); //Reads standard error
cout<<"\n Printing the standard output..........\n";
cout<<endl<<StdOut.toStdString();
bool mouse1 = StdOut.contains("ID 046d:c03e");
bool keyBoard1 = StdOut.contains("ID 413c:1003");
if (mouse1 ==1 && keyBoard1==1)
{
// start main program
// revoke A signal to tell QML the correct devices are connected
usbdeviceid->setMouse1Detected(1);
usbdeviceid->setkeyBoard1Detected(1);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
}
}
}
}
It is not necessary to create infinite loops in Qt, instead the most elegant thing is to use the signals.
#include <QGuiApplication>
#include <QProcess>
#include <QQmlApplicationEngine>
class LSUSB: public QObject
{
Q_OBJECT
public:
LSUSB(const QStringList & ids, QObject *parent=nullptr): QObject(parent), status(false), ids(ids)
{
QString command = "lsusb";
connect(&process, &QProcess::readyReadStandardOutput, this, &LSUSB::onReadyReadStandardOutput);
connect(&process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, &LSUSB::onFinished);
process.setProgram(command);
process.start();
}
Q_SIGNALS:
void isLoaded();
private Q_SLOTS:
void onReadyReadStandardOutput(){
QString stdout = process.readAllStandardOutput();
status = true;
for(const QString & id: ids){
status &= stdout.contains(id);
}
if(status){
process.kill();
Q_EMIT isLoaded();
}
}
void onFinished(){
if(!status)
process.start();
}
private:
QProcess process;
bool status;
QStringList ids;
};
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
LSUSB lsusb({"ID 046d:c03e", "ID 413c:1003"});
USBdeviceID usbdeviceid;
QObject::connect(&lsusb, &LSUSB::isLoaded, [&engine, &usbdeviceid](){
usbdeviceid.setMouse1Detected(1);
usbdeviceid.setkeyBoard1Detected(1);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
QCoreApplication::exit(-1);
});
return app.exec();
}
#include "main.moc"
Got an error running the following problem:
#include <QMessageBox>
#include <QApplication>
int main() {
QApplication app();
QMessageBox msgBox(QMessageBox::Critical,
QObject::tr("text1"),
QObject::tr("text2"),
QMessageBox::Ok);
msgBox.exec();
return 0;
}
The error is:
The program breaks at QMessageBox msgBox(...);
The call stack is:
EDIT: Even after i have added QApplication instance in XTerm window named qtcreator_process_stub i see the following:
QWidget: Must construct QApplication before a QWidget
The line
QApplication app();
doesn't create a QApplication object - it actually declares a function taking no arguments and returning a QApplication! This is sometimes known as the "most vexing parse".
To actually construct the application object, you need to provide the program's arguments:
QApplication app(argc, argv);
The full program is then
#include <QMessageBox>
#include <QApplication>
int main(int argc, char **argv) {
QApplication app(argc, argv);
QMessageBox msgBox(QMessageBox::Critical,
QObject::tr("text1"),
QObject::tr("text2"),
QMessageBox::Ok);
msgBox.exec();
return 0;
}
I've created a Qt Quick 2.5 app and connected signals and slots to my C++ module,
I only can send signals from C++ and activate QML slots, but I can't receive QML signals on Qt side.
Here is main.cpp:
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/qml/main.qml")));
AlfredApp(engine.rootObjects().first());
return app.exec();
}
here is my QML code which holds the signal:
MouseArea {
id: mainButtonMouseArea
objectName: "mainButtonMouseArea"
anchors.fill: parent
signal signalClicked()
onClicked: {
console.log("clicked")
signalClicked()
}
}
I always get the console message from QML when I click on the MouseArea.
Here is my c++ constructor:
AlfredApp::AlfredApp(QObject* viewRootObject, QObject* parent)
: QObject(parent), d(new Private)
{
d->viewRootObject = viewRootObject;
d->viewMainButton = viewRootObject->findChild<QObject*>("mainButton");
d->viewMainButtonIcon = viewRootObject->findChild<QObject*>("mainButtonIcon");
d->viewMainButtonMouseArea = viewRootObject->findChild<QObject*>("mainButtonMouseArea");
// Signals/Slots connection
connect(d->viewMainButtonMouseArea, SIGNAL(signalClicked()),
this, SLOT(mainButtonClicked()));
connect(this, SIGNAL(signalListening()),
d->viewMainButtonIcon, SLOT(listening()));
connect(this, SIGNAL(signalProcessing()),
d->viewMainButtonIcon, SLOT(processing()));
}
Here is my slot that never gets called:
void AlfredApp::mainButtonClicked()
{
qDebug() << "Main Button Clicked";
}
BTW, are there some qml code examples that have slots/function that respond normally to C++ signals
Just for testing, could you connect the signal and the slot in main.cpp?
Something like this:
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/qml/main.qml")));
QObject *rootObj = engine.rootObjects().first();
QObject *item = rootObj->findChild<QObject*>("mainButtonMouseArea");
AlfredApp alfredapp(rootObj);
QObject::connect(item, SIGNAL(signalClicked()),
&alfredapp, SLOT(mainButtonClicked()));
return app.exec();
}
This should work. If not, try the idea suggested by #hyde.
Here you have the sample code.
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QDialog dlg;
dlg.exec();
return a.exec();
}
That's all my code, but when I close the window, The process isn't exit, it seems that drop in the loop a.exec().
Generally speaking, calling any exec is a bad idea, other than QCoreApplication::exec() or QDrag::exec(). The presence of exec() and waitForXxx() methods is an enticing trap for the unwary. Those methods are "easy" to use, but that ease comes at a price of hard to track bugs. Don't use them.
You should simply show the dialog:
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QMessageBox msg;
msg.setText("Hello");
msg.addButton(QMessageBox::Close);
msg.show();
return a.exec();
}
If you wish to wait for the dialog to be accepted or rejected, you should use the dialog's clickedButton slot. QMessageBox has a long-standing bug that makes the accepted and rejected signals useless :(
// https://github.com/KubaO/stackoverflown/tree/master/questions/messagebox-show-25545652
#include <QtGui>
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
#include <QtWidgets>
#endif
#include <functional>
[...]
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QMessageBox msg;
msg.setText("Continue?");
msg.addButton(QMessageBox::Yes);
msg.addButton(QMessageBox::No);
auto onClick = [&msg]() {
auto role = msg.buttonRole(msg.clickedButton());
if (role == QMessageBox::NoRole)
QApplication::quit();
if (role == QMessageBox::YesRole) {
auto label = new QLabel("I'm running");
label->setAttribute(Qt::WA_DeleteOnClose);
label->show();
}
};
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
QObject::connect(&msg, &QMessageBox::buttonClicked, onClick);
#else
QObject::connect(&msg, SIGNAL(buttonClicked(QAbstractButton*)),
new FunctorSlot{onClick, &msg}, SLOT(call()));
#endif
msg.show();
return app.exec();
}
#include "main.moc"
For Qt 4, you need the following helper:
// Qt 4 only
struct FunctorSlot : public QObject {
Q_OBJECT
public:
std::function<void()> callable;
template <typename Fun>
FunctorSlot(Fun && fun, QObject * parent = {}) :
QObject{parent}, callable{std::forward<Fun>(fun)} {}
Q_SLOT void call() {
callable();
}
};
Possible solution:
QApplication a(argc, argv);
QDialog dlg;
QTimer::singleShot( &dlg, 0, SLOT(exec()) );
return a.exec();
It will work well. First - application event loop will be started. Then dialog event loop will be executed. After closing of dialog, both dialog and application loop will be finished. Application loop will be terminated automatically (by default), when last window is closed.
But, as noted by #thuga - there are no reason to call exec(). It is enough to call show() method.