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.
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();
}
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.
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.
Using the TreeModel from this tutorial:
http://qt-project.org/doc/qt-4.8/itemviews-simpletreemodel.html
this version works (shows the tree):
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
MainWindow mainWin;
QFile file("default.txt");
file.open(QIODevice::ReadOnly);
TreeModel model(file.readAll());
file.close();
QTreeView *treeView = new QTreeView(mainWin.splitter);
treeView->setModel(&model);
mainWin.show();
return app.exec();
}
class MainWindow: public QMainWindow {
QSplitter* splitter;
public:
MainWindow() : QMainWindow() {
splitter = new QSplitter(Qt::Horizontal, this);
splitter->setMinimumSize(1000,1000);
}
};
and this one doesn't work:
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
MainWindow mainWin;
mainWin.show();
return app.exec();
}
class MainWindow: public QMainWindow {
QSplitter* splitter;
public:
MainWindow() : QMainWindow() {
splitter = new QSplitter(Qt::Horizontal, this);
splitter->setMinimumSize(1000,1000);
QFile file("default.txt");
file.open(QIODevice::ReadOnly);
TreeModel model(file.readAll());
file.close();
QTreeView *treeView = new QTreeView(splitter);
treeView->setModel(&model);
}
};
What happens here? Is there some API misuse / undefined behavior?
I assume that with "doesn't work" you mean that the tree view stays empty.
You create the TreeModel model on the stack. That means it will be destroyed at the end of the block. In the first case, that's not a problem, because main() won't be exited before the application quits (i.e. app.exec() returns).
In the second case it is a problem, as the model will be destroyed right away at the end of the MainWindow constructor, i.e. right away, before the window is even visible.
You must create the model either on the heap (don't forget about memory management then - pass the main window (this) as parent) or make it a member variable.
I dont know how to pass parameters from QML file to c++ file in Qt.
QML code:
import QtQuick 1.1
Rectangle{
id:loin
height: 272
width:480
property alias loguid:loginuid
signal sigHome()
Rectangle{
id:rect1
width:parent.width-80
height:24
TextInput {
id:loginuid
maximumLength: 16
width: maximumLength * 20
focus: false
validator: RegExpValidator { regExp: /\d+/ }
KeyNavigation.down: login1
}
}
Button{
id: login1
x: 195
y: 187
height:30;
focus:false
border.color:"black"
opacity: activeFocus ? 1.0 : 0.5
Text{
text:"LOGIN"
anchors.horizontalCenter:login1.horizontalCenter;
anchors.verticalCenter:login1.verticalCenter;
}
Keys.onReturnPressed: {
if(loginuid.text < 1000000000000000)
{
text1.opacity=0.1
error1.visible=true
errorText.text="\n enter valid 16 digit number\n"
errorOk.focus=true
loginuid.focus=false
}
else{
loginuid.focus=false
loin.sigHome()
}
}
}
}
c++ code:
#include <QApplication>
#include <QDeclarativeView>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
int uid;
QDeclarativeView view;
view.setSource(QUrl::fromLocalFile("main.qml"));
view.show();
return app.exec();
}
When I press the login button rect1.text content shud go to main.cpp file and uid in the main.cpp get dat value. Something like this uid=rect1.text.
How to do it?
I wouldn't try to listen for a QML signal from the C++ side. Calling a C++ method with arguments is much easier and achieves the same:
To do so you have to:
define a slot or invokable method accepting the required arguments
register the class carrying the method with the declarative engine
then you can set an instance of this class as a property of your root context and finally call this method from QML
This topic is also well covered in the official documentation.
Thanks, sebasgo, your response helped me. I used signals and slots to communicate.
I created a signal in main.qml.
signal info(string msg)
and in login page
else{
info(loginUid.text)
loginuid.focus=false
loin.sigHome()
}
and in main.cpp I connected it to d slot
main.cpp goes like this
#include <QtGui>
#include <QApplication>
#include <QDeclarativeView>
#include <QtDeclarative>
class DeclarativeView : public QDeclarativeView
{
Q_OBJECT
public:
DeclarativeView(const QUrl & source) : QDeclarativeView(source)
{
}
public slots:
void readText(QString quid)
{
qdebug<<quid;
}
};
#include "main.moc"
int main(int argc, char *argv[])
{
QString file = "main.qml";
QApplication app(argc, argv);
DeclarativeView view(QUrl::fromLocalFile(file));
QDeclarativeItem *item = qobject_cast<QDeclarativeItem *>(view.rootObject());
QObject::connect(item, SIGNAL(info(QString)), &view, SLOT(readText(QString)));
view.show();
return app.exec();
}
Create a GUI controller C++ class:
class UiController : public QObject
{
Q_OBJECT
public:
UiController();
virtual ~UiController();
public slots:
void cal_daysoff__onDoubleClicked(const QDate& date);
};
In QML file you define, say, a calendar control in which you connect a signal to a slot in the controller:
Calendar{
id: cal_daysoff
Layout.fillWidth: true
Layout.fillHeight: true
onDoubleClicked: UiController.cal_daysoff__onDoubleClicked(date)
}
In main file, when launching the QML interface, connect the interface to the controller:
#include "uicontroller.h"
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
UiController control;
engine.rootContext()->setContextProperty("UiController", &control);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}