QQuickWindow in shared lib auto close when show in QApplication - c++

Question

I develop a generic interface library with qt. I have trouble with pressed effect on QPushbutton when I click with a touch screen (this effect appears one time on 10 click).
So I create a basic qml application with one button and pressed effect appear all time. I incude the qml part into my library and load it in QQuickWidget and I have same problem with pressed effect.
So I want to use only qml. My principal application is a QApplication and I load my library in it in which I load qml file with QQmlApplication Engine. Then I show it by QQuickWindow.
When I launch my application I saw the window open but it is automatically close. I think my QApplication don't detect QML and the renderer loop is not start.
I'm on windows with QT5.5.1 (MSVC2013, 32bit)
pro file of main application
QT += core xml widgets qml quick
TARGET = COM_INT
CONFIG += console
CONFIG -= app_bundle
TEMPLATE = app
SOURCES += main.cpp \
comint.cpp
HEADERS += \
comint.h \
INCLUDEPATH += "$$(My_Workspace)/Modules_Generique/IHM_Soft"
Release{
LIBS += "$$(My_Workspace_build)/IHM_Soft/release/IHM_Soft.lib"
}
Debug{
LIBS += "$$(My_Workspace_build)/IHM_Soft/debug/IHM_Soft.lib"
}
Main application (exe) main.cpp
#include <QApplication>
#include <QQmlApplicationEngine>
#include "comint.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
ComInt com;
com.initialize();
return a.exec();
}
ComInt class:
Source file comint.cpp
#include "comint.h"
#include "ihmsoft.h"
ComInt::ComInt()
{
}
void ComInt::initialize()
{
this->m_pIHMSoft = new IHMSoft();
}
header file comint.h
#ifndef COMINT_H
#define COMINT_H
class IHMSoft;
class ComInt
{
public:
ComInt();
void initialize();
private:
IHMSoft *m_pIHMSoft;
};
#endif // COMINT_H
pro file of shared lib
QT += xml widgets core qml quick quickwidgets
CONFIG += c++11
TARGET = IHM_Soft
TEMPLATE = lib
DEFINES += IHM_SOFT_LIBRARY
SOURCES += ihmsoft.cpp
HEADERS += ihmsoft.h\
ihm_soft_global.h
RESOURCES += \
rsc.qrc
Shared library: source file ihm_soft.cpp
#include "ihmsoft.h"
#include <QQmlApplicationEngine>
#include <QQuickWindow>
IHMSoft::IHMSoft(){
qputenv("QT_QUICK_CONTROLS_STYLE", "Base");
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/IHM_Soft.qml")));
QList<QObject*> root = engine.rootObjects();
QQuickWindow *window = qobject_cast<QQuickWindow*>(root.at(0));
window->show();
}
header file ihm_soft.h
#ifndef IHM_SOFT_H
#define IHM_SOFT_H
#include "ihm_soft_global.h"
class IHM_SOFT_SHARED_EXPORT IHM_Soft
{
public:
IHM_Soft();
};
#endif // IHM_SOFT_H
Global file ihm_soft_global.h
#ifndef IHM_SOFT_GLOBAL_H
#define IHM_SOFT_GLOBAL_H
#include <QtCore/qglobal.h>
#if defined(IHM_SOFT_LIBRARY)
# define IHM_SOFT_SHARED_EXPORT Q_DECL_EXPORT
#else
# define IHM_SOFT_SHARED_EXPORT Q_DECL_IMPORT
#endif
#endif // IHM_SOFT_GLOBAL_H
Qml file
import QtQuick 2.0
import QtQuick.Controls 1.4
import QtQuick.Window 2.0
ApplicationWindow {
visible: true
width: 500
height: 500
Button {
visible: true
iconSource: "resources/t_on_off.png"
}
}
Edit: Sorry the code of the main application was a test application which do not include lib.

Answer 1

A variable is deleted when its scope ends, in your case engine is a local variable that is deleted when IHMSoft finishes being built, so you see that the window closes. The solution is to make it a member of the class:
*.h
#ifndef IHM_SOFT_H
#define IHM_SOFT_H
#include "ihm_soft_global.h"
#include <QQmlApplicationEngine>
class IHM_SOFT_SHARED_EXPORT IHM_Soft
{
public:
IHM_Soft();
private:
QQmlApplicationEngine engine; // member
};
#endif // IHM_SOFT_H
*.cpp
#include "ihmsoft.h"
IHMSoft::IHMSoft(){
qputenv("QT_QUICK_CONTROLS_STYLE", "Base");
engine.load(QUrl(QStringLiteral("qrc:/IHM_Soft.qml")));
}