C++ to change QML object properties

Vignes

I'm getting error "main.obj:-1: error: LNK2019: unresolved external symbol "public: __cdecl iObject::iObject(class QObject *)" (??0iObject@@QEAA@PEAVQObject@@@Z) referenced in function main"

p3c0

Have you included its corresponding header file (probably iobject.h) in main.cpp ?

Vignes

Yes
main.cpp
@
#include "iobject.h"
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QtQuick/QQuickWindow>

int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);

QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:///main.qml")));

QQuickWindow *W = (QQuickWindow *)engine.rootObjects().first();
iObject a(W);
QObject::connect(engine.rootObjects().first(),SIGNAL(callCpp()),&a,SLOT(onCallCpp()));

return app.exec();

}
@

p3c0

Can you post the new iobject.cpp and .h file ?

Vignes

iobject.h
@
#ifndef IOBJECT_H
#define IOBJECT_H

#include <QObject>

class iObject : public QObject
{
Q_OBJECT
public:
explicit iObject(QObject *parent = 0);

signals:

public slots:

};

#endif // IOBJECT_H
@

iobject.cpp
@
#include "iobject.h"

iObject::iObject(QObject *parent) :
QObject(parent)
{
}
@

p3c0

Everything seems to be fine to me.
Try to clean, run qmake and build the project again.
Apart from that declare the SLOT onCallCpp in iObject class.

Vignes

Still same error, the
@
iObject a(W);
@

Creates following errors:
"main.obj:-1: error: LNK2019: unresolved external symbol "public: _cdecl iObject::iObject(class QObject *)" (??0iObject@@QEAA@PEAVQObject@@@Z) referenced in function main""
And
"debug\HEVC.exe:-1: error: LNK1120: 1 unresolved externals
"
I tried cleaning and rebuild it and created a new project and tried it, same error

All the code in new project follows:
main.qml
@
import QtQuick 2.2
import QtQuick.Window 2.1

Window {
visible: true
width: 360
height: 360

MouseArea {
    anchors.fill: parent
    onClicked: {
        Qt.quit();
    }
}

Text {
    text: qsTr("Hello World")
    anchors.centerIn: parent
}

}
@

main.cpp
@
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QtQuick/QQuickWindow>
#include "iobject.h"

int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);

QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
QQuickWindow *W = (QQuickWindow *)engine.rootObjects().first();
    iObject a(W);
    QObject::connect(engine.rootObjects().first(),SIGNAL(callCpp()),&a,SLOT(onCallCpp()));

return app.exec();

}
@

iobject.h
@
#ifndef IOBJECT_H
#define IOBJECT_H

#include <QObject>

class iObject : public QObject
{
Q_OBJECT
public:
explicit iObject(QObject *parent = 0);

signals:

public slots:
void onCallCpp();

};

#endif // IOBJECT_H
@

iobject.cpp
@
#include "iobject.h"

iObject::iObject(QObject *parent) :
QObject(parent)
{
}
@

I went though several examples and foud ""Animated Tiles":http://qt-project.org/doc/qt-4.8/animation-animatedtiles.html" example. This one uses different library like QtWidgets, QtCore/qstate.h and main.moc. here not QML. This is an old version qt-4.8 as well.

I'm now wondering, that am I using the right QT tool for my project, which uses 4K video playing, editing, analytics tools with the support of OpenGL to be implimented using Cpp.

I chose QML, because of built in OpenGL, and Cpp and JS support. Now Qt Widgets, Qt Quick Application, Qt Quick UI and old version, new version are confusion to me.

It would be great, If you could please help me with these.

Thank you

p3c0

Have the files iobject.cpp and .h included in the project structure from Qt Creator?
I have created a small test app based upon the example.
Here's the "Link":https://docs.google.com/file/d/0B3rkZH6q1E7ocTdnOFQwNVBDM2c/edit?pli=1
Please check if it works.

Also Animated Tiles is a completely different example. It doesnot use Qt Quick.
Please do not go over to Qt 4.8 or less. It's lot different from Qt 5.3

You can refer Qt 5 docs for more information.
Following are good links
"http://qt-project.org/doc/qt-5/qtqml-index.html":http://qt-project.org/doc/qt-5/qtqml-index.html
"http://qt-project.org/doc/qt-5/qtqml-cppintegration-topic.html":http://qt-project.org/doc/qt-5/qtqml-cppintegration-topic.html

Let me know if the Sample Application works.

Vignes

Thanks, your sample works. I got main working after deleting the build folder. Some reason cleaning didn't work, even when I copy and pasted your code.

I was thinking like this, creating object and connecting it to QML types:
iObject A
A.screenSize (connect to Window : visibility)
A.textApped (connect to Text : text)
A.animantionStart (connect to Animation : start)

Then changing it in cpp and then emitting signal or even creating, changing & destroying QML types in cpp. Like JavaScript in HTML application.

If you can provide this type of sample works on would be very grateful.

*Note: I learn using simple working example rather than reading text with pieces of code, because of my DYSLEXIA.

p3c0

You can also use "QMetaObject::invokeMethod":http://qt-project.org/doc/qt-5/qmetaobject.html#invokeMethod to call a javascript function inside a QML and in that function you can do the operations.
For eg.
Test.qml
@
Window {
visible: true
width: 400
height: 400

function changeColor() {
    rect.color="blue"
}

Rectangle {
    id: rect
    anchors.fill: parent
    color: "red"
}

}
@

and to call it from main.cpp

@
QMetaObject::invokeMethod(engine.rootObjects().first(), "changeColor");
@

You can also keep these calls in separate cpp methods of the iObject class.

Vignes

Say I have following main.qml
@
Window {
visible: true
width: 400
height: 400

Rectangle {
id: rect
anchors.fill: parent
color: "red"

    Text {
    id: mytext
    text: qsTr("<b>Hello World!</b>")
    color: "blue"
    }
    MouseArea {
    anchors.fill: parent
    onClicked: {
        Qt.quit();}
    }
}

}
@

How do I use this "const char * QMetaObject::className() const" to get Text object name.

How do I use "QMetaProperty::write(QObject * object, const QVariant & value) const" to change text value

Thank you

p3c0

bq. How do I use this “const char * QMetaObject::className() const” to get Text object name.

As shown earlier you can find the exact Item using findChild and then use "metaObject()":http://qt-project.org/doc/qt-5/qobject.html#metaObject to get it's corresponding metaObject and then use it to get "className()":http://qt-project.org/doc/qt-5/qmetaobject.html#className;

bq. How do I use “QMetaProperty::write(QObject * object, const QVariant & value) const” to change text value

This kind of bit tedious, you have to first findChild then get it's metaObject and then iterate over it to find the exact index of the "property":http://qt-project.org/doc/qt-5/qmetaobject.html#property which you want to set and then change the property for that particular index using "write":http://qt-project.org/doc/qt-5/qmetaproperty.html#write

Alternatively you use more user friendly "setProperty":http://qt-project.org/doc/qt-5/qobject.html#setProperty to directly set it instead of first iterating,finding and then changing.

Vignes

how do I fix the following issue
@
MouseArea {
id: oneClick
anchors.fill: parent
onClicked: opacity_1.running = true;
}
MouseArea {
id: twoClick
anchors.fill: parent
onDoubleClicked: window1.callCpp()
}
@

Thank you

Vignes

How do I use access mouse right click? I tried the following without success:
@
onClicked: {if(mouse.button == Qt.RightButton){if(menu.opacity == 0){opacity_1.running = true;}}}
@
and
@
onPressed: {if(mouse.button == Qt.RightButton){if(menu.opacity == 0){opacity_1.running = true;}}}
@

Vignes

Could you tell me how to set-up Git in QtCreator Option > Version Control: Configuration, Miscellaneous, Gitk and Repository Browser ?

Thank you

Vignes

What am I doing wrong here :
I have included <QScreen>
@
QScreen *screen;
qDebug() << "Information for screen:" << screen->name();
qDebug() << " Available geometry:" << screen->availableGeometry().x() << screen->availableGeometry().y() << screen->availableGeometry().width() << "x" << screen->availableGeometry().height();
qDebug() << " Available size:" << screen->availableSize().width() << "x" << screen->availableSize().height();
qDebug() << " Available virtual geometry:" << screen->availableVirtualGeometry().x() << screen->availableVirtualGeometry().y() << screen->availableVirtualGeometry().width() << "x" << screen->availableVirtualGeometry().height();
qDebug() << " Available virtual size:" << screen->availableVirtualSize().width() << "x" << screen->availableVirtualSize().height();
qDebug() << " Depth:" << screen->depth() << "bits";
qDebug() << " Geometry:" << screen->geometry().x() << screen->geometry().y() << screen->geometry().width() << "x" << screen->geometry().height();
qDebug() << " Logical DPI:" << screen->logicalDotsPerInch();
qDebug() << " Logical DPI X:" << screen->logicalDotsPerInchX();
qDebug() << " Logical DPI Y:" << screen->logicalDotsPerInchY();
@
Help please

p3c0

[quote author="Vignes" date="1406045743"]how do I fix the following issue
@
MouseArea {
id: oneClick
anchors.fill: parent
onClicked: opacity_1.running = true;
}
MouseArea {
id: twoClick
anchors.fill: parent
onDoubleClicked: window1.callCpp()
}
@

Thank you[/quote]

What is the problem ? You need to elaborate.

bq. onClicked: {if(mouse.button == Qt.RightButton){if(menu.opacity == 0){opacity_1.running = true;}}}

set acceptedButtons: Qt.LeftButton | Qt.RightButton for MouseArea

bq.
QScreen *screen;
qDebug() << "Information for screen:" << screen->name();
.
.
.

@
QScreen *screen = QGuiApplication::primaryScreen();
qDebug() << screen->availableGeometry();
@

p3c0

[quote author="Vignes" date="1406047246"]Could you tell me how to set-up Git in QtCreator Option > Version Control: Configuration, Miscellaneous, Gitk and Repository Browser ?

Thank you[/quote]

May be "this":https://qt-project.org/doc/qtcreator-2.8/creator-version-control.html#using-version-control-systems and a youtube tutorial "here":http://www.youtube.com/watch?v=3Dr05-bFMbw help you. I have never used git from Qt Creator, so can't help you that much on it. I normally do it through command line.

Vignes

I tried to add two mouse area function on main window: double clicked and a clicked like below:
@
MouseArea {
id: oneClick
anchors.fill: parent
onClicked: opacity_1.running = true;
}
MouseArea {
id: twoClick
anchors.fill: parent
onDoubleClicked: window1.callCpp()
}
@

Here only the last muse area function works. So I tried merging two and it works :
@
MouseArea {
id: windowClicks
anchors.fill: parent
onClicked: if(menu.opacity == 0){opacity_1.running = true;}{opacity_1.running = true;}}}
onDoubleClicked: window1.callCpp()
}
@

I wanted a mouse area function for right mouse clicked, for this I tried the bellow:
@
onPressed: {if(mouse.button == Qt.RightButton){if(menu.opacity == 0){opacity_1.running = true;}}}
@

Here it did not work, but if I change the "Qt.RightButton" to "Qt.LeftButton" it works

Is there any other way to add multiple mouse event to one area?

How do I use the Right click to run a function?

Is it possible to add or modify or remove mouse event in cpp?

Thanks

p3c0

bq. Is there any other way to add multiple mouse event to one area?

Yes. You just did it by adding onClicked and onDoubleClicked event handler to mousearea

bq. How do I use the Right click to run a function?

As I said earlier you need to set acceptedButtons
@
MouseArea {
id: twoClick
anchors.fill: parent
acceptedButtons: Qt.LeftButton | Qt.RightButton
onClicked: {
if(mouse.button==Qt.RightButton) {
console.log("Right Click")
}
}
}
@

bq. Is it possible to add or modify or remove mouse event in cpp?

You can set enabled property from C++ by finding child as shown earlier.