I have a Qt Quick project and I just added some source files. When trying to build I get the error message:
QWidget: Cannot create a QWidget without QApplication
Since I have a Qt Quick project I use the QGuiApplication. QApplication is a subclass of QGuiApplication. How do I make QApplication available to the newly added sources? Or how do one solve it when one have a Qt Quick and a QWidget?
The source files are the QCustomPlot library which shows a graph.
EDIT:
main.cpp:
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QtQuick2ApplicationViewer viewer;
//Register C++ classes with QML
qmlRegisterType<Bluetooth>("Bluetooth", 1, 0, "Bluetooth");
//Set start QML file
viewer.setMainQmlFile(QStringLiteral("qml/test/main.qml"));
//New Code:
// generate some data:
QWidget widget;
QCustomPlot * customPlot = new QCustomPlot(&widget);
QVector<double> x(101), y(101); // initialize with entries 0..100
for (int i=0; i<101; ++i)
{
x[i] = i/50.0 - 1; // x goes from -1 to 1
y[i] = x[i]*x[i]; // let's plot a quadratic function
}
// create graph and assign data to it:
customPlot->addGraph();
customPlot->graph(0)->setData(x, y);
// give the axes some labels:
customPlot->xAxis->setLabel("x");
customPlot->yAxis->setLabel("y");
// set axes ranges, so we see all data:
customPlot->xAxis->setRange(-1, 1);
customPlot->yAxis->setRange(0, 1);
customPlot->replot();
//New Code End
//Show GUI
viewer.showExpanded();
return app.exec();
}
Error:
QML debugging is enabled. Only use this in a safe environment.
QWidget: Cannot create a QWidget without QApplication
Invalid parameter passed to C runtime function.
Invalid parameter passed to C runtime function.
The QApplication class manages the GUI application's control flow and main settings. QApplication contains the main event loop, where all events from the window system and other sources are processed and dispatched. It also handles the application's initialization, finalization, and provides session management.
It initializes the application with the user's desktop settings such as palette(), font() and doubleClickInterval(). It keeps track of these properties in case the user changes the desktop globally, for example through some kind of control panel.
[static] int QApplication::exec() Enters the main event loop and waits until exit() is called, then returns the value that was set to exit() (which is 0 if exit() is called via quit()). It is necessary to call this function to start event handling.
Creating and Running QML Projects For simple UI files such as this one, select File > New File or Project > Application (Qt Quick) > Qt Quick Application - Empty from within Qt Creator. Pressing the green Run button runs the application. You should see the text Hello, World! in the center of a red rectangle.
The key concept is QWidget::createWindowContainer(). Try the following code:
#include <QQuickView>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQuickView *view = new QQuickView();
QWidget *container = QWidget::createWindowContainer(view, this);
container->setMinimumSize(200, 200);
container->setMaximumSize(200, 200);
container->setFocusPolicy(Qt::TabFocus);
view->setSource(QUrl("qml/test/main.qml"));
...
}
You can find the details on the following posts:
Introducing QWidget::createWindowContainer()
Combining Qt Widgets and QML with QWidget::createWindowContainer()
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With