C++ to change QML object properties

Vignes

I want to change QML objects properties using C++.
I tried the “http://qt-project.org/doc/qt-5/qml-qtqml-qtobject.html”. I couldn’t get it working on QT5.3.
If anyone could provided working example for QT5.3 would be great help either “QT Declarative” or “QTObject”.

p3c0

Hi,

Are you using QQuickView or QQmlApplicationEngine ?

Vignes

Hi,
I am using both. below my main.cpp code:

@
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QObject>
#include <QtQuick/QQuickView>
#include <QtQuick/QQuickItem>

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

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

QQuickView view;
view.setSource(QUrl::fromLocalFile&#40;"main.qml"&#41;&#41;;

// view.show();

QQuickItem *item = view.rootObject()->findChild<QQuickItem*>("myRect");
if (item)
    item->setProperty("color", QColor(Qt::yellow));

return app.exec&#40;&#41;;

}

main.qml code:

import QtQuick 2.1
import QtQuick.Window 2.1

//import QtQuick 2.0
//import QtQuick.Window 2.0

Window {
visible: true
width: 360
height: 360

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

Text {
    text: qsTr("Hello World")
    anchors.centerIn: parent
}
Item {
    width: 200; height: 200

    Rectangle {
        anchors.fill: parent
        color: "red"
        objectName: "myRect"
    }
}

}
@

I want the color to change.

[edit: added missing coding tags @ SGaist]

p3c0

Please encapulate your code in the code tags '@@' so that its easily readable to others.

You should either use QQmlApplicationEngine or QQuickView not both.
If using QQmlApplicationEngine you can try
@
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
QQuickItem item = engine.rootObjects().at(0)->findChild<QQuickItem>("myRect");
if (item) {
item->setProperty("color", QColor(Qt::yellow));
}
return app.exec();
@

Vignes

Hi,
Thank you very much. It works fine.
Is it possible to control animation using C++?

I am testing code tags:
@
#include <QQmlApplicationEngine>
//#include <QObject>
//#include <QtQuick/QQuickView>
#include <QtQuick/QQuickItem>

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

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

// QQuickView view;
// view.setSource(QUrl::fromLocalFile("main.qml"));
// view.show();

QQuickItem *item = engine.rootObjects().at(0)->findChild<QQuickItem*>("myRect");
if (item)
    item->setProperty("color", QColor(Qt::yellow));

return app.exec();

}
@

p3c0

In the same way as above you can set the "running" property of animation so that you can start or stop the animation or set other properties.

Vignes

Hi,
I try to change width and height of object, but I'm couldn't

qml
@
Window {
visible: true
width: 360
height: 360
objectName: "myWindow"
}
@

main.cpp
@
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QtQuick/QQuickItem>

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

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

// QQuickView view;
// view.setSource(QUrl::fromLocalFile("main.qml"));
// view.show();

QQuickItem *item = engine.rootObjects().at(0)->findChild<QQuickItem*>("myWindow");
if (item)
    item->setProperty("width", QWidth(Qt::560));

return app.exec();

}
@

Could you help.

Thank you

p3c0

Hi,

There are multiple problems here,

"Window":http://qt-project.org/doc/qt-5/qml-qtquick-window-window.html doesn't instantiate QQuickItem but QQuickWindow. So you can't cast it to QQuickItem.
There's nothing like QWidth or Qt::560, just plainly use the number e.g 560
Window is a top level, so you can get it directly instead of finding.

To sum up, try this,
@
QQuickWindow *item = (QQuickWindow *)engine.rootObjects().first();
if (item)
item->setProperty("width", 1360);
@

Vignes

Hi,
I tried to change QML Window to fullscreen using visibility via c++
@
QQuickWindow *W = (QQuickWindow *)engine.rootObjects().first();
if (W)
W->setProperty("visibility", "Fullscreen");
@
tried
@
W->FullScreen;
@
tried
@
W->visibility() = "Fullscreen";
@

none of them are working. Help please?

Vignes

Hi,
I got it working, it the spelling of the Fullscreen should be "FullScreen"
@
QQuickWindow *W = (QQuickWindow *)engine.rootObjects().first();
if (W)
W->setProperty("visibility", "FullScreen");
@

p3c0

For FullScreen you can use directly,

@
if (W)
W->showFullScreen();
@

Vignes

Hi,
I have objects window, text and mouse area to text in qml document and I want to implement in c++: when text area is clicked: if the window is not on fullscreen, it should become fullscreen and the text in the text are should change to "Window is Fullscreen" with a animated color chage to "white". Next time it clicked it should come out of fullscreen and chanege the text and color. Also console.log equivalent output of the this event along with screen resolution should be output from c++ (not via qml).

main.qml :
@
import QtQuick 2.2
import QtQuick.Window 2.1

Window {
id: window1
visible: true
width: 360
height: 360
color: "red"
title: "MyWindow"

Text {
    objectName: "myText"
    text: qsTr("Hello World!<br><i>I'm </i><b>not Fullscreen<i> Now</i></b>")
    font.bold: true
    horizontalAlignment: Text.AlignHCenter
    font.family: "Times New Roman"
    font.pointSize: 18
    anchors.centerIn: parent
    color: "steelblue"

    MouseArea {
        anchors.fill: parent
    }
}

}
@

main.cpp
@
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QtQuick/QQuickItem>
#include <QtQuick/QQuickWindow>

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

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

//here I need function for
//1 clicke event
//check fullscreen value
//2 text changing
//3 animation
//4 console.log output of Screen resolution and action
//5 finaly Window : showMaximized(); or showFullScreen();

return app.exec();

}
@

Could you help me with this please?
Thank you

p3c0

You can,

Create a QObject based class
Create a SLOT in it
Pass QQuickWindow pointer (which we obtained as shown above) to it
Create a signal in your QML
Do the connections
In the created class cast the QObject pointer to QQuickWindow using qobject_cast
Use this pointer to access/modify the properties of the QML window in the SLOT when the SIGNAL is fired from QML

Vignes

Hi,
I created QObject: called iobject.h
@
#ifndef IOBJECT_H
#define IOBJECT_H

#include <QObject>

class iObject : public QObject
{
Q_OBJECT
Q_PROPERTY(QString name READ name WRITE setName)
public:
explicit iObject(QObject *parent = 0);

QString name() const;

    Q_INVOKABLE void nameChang();

signals:
void nameChanged(int newValue);

public slots:
void setName(const QString &name);

private:
QString m_name;
};

#endif // IOBJECT_H
@

iobject.cpp
@
#include "iobject.h"

iObject::iObject(QObject *parent) :
QObject(parent)
{
}
QString iObject::name() const
{
return m_name;
}
iObject::setName(const QString &name){
if(name != m_name)
m_name = name;
emit nameChanged(name);
}
@

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

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

qmlRegisterType<iObject>("myObject", 1, 0, "iObject");

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

return app.exec();

}
@

main.qml
@
import QtQuick 2.2
import QtQuick.Window 2.1
import myObject 1.0

Window {
visible: true
width: 360
height: 360
title: iObject.name

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

Text {
    text: qsTr("Hello World!<br><i>I'm </i><b>not Fullscreen<i> Now</i></b>")
    horizontalAlignment: Text.AlignHCenter
    font.family: "Times New Roman"
    font.pointSize: 18
    anchors.centerIn: parent
    color: "steelblue"

    MouseArea {
        anchors.fill: parent
    }
}

}
@

At this point, It did not work. erros on main.cpp 'qmlRegisterType'
what am I doing wrong?

p3c0

Just create a the class and pass the QQuickWindow pointer. No need use qmlRegisterType.
Something like this,
main.cpp
@
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()));
@

No need of custom properties in the class.
Remember to cast back QObject back to QQuickWindow in iObject and then you can modify QQuickWindow properties as shown earlier.

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)
{
}
@