Connect qml object property changes to signal/slot mechanism - c++

Question

I got this basic project:
main.qml
Rectangle{
Text {
id: text1
objectName: "showStr"
property string _textField: "passive"
text: _textField
}
Button{
id: _button
signal buttClick(string str)
anchors.top: text1.bottom
text: "Button"
onClicked:
{
_button.buttClick("state: active")
}
}
}
myClass.cpp
class myClass : public QObject{
Q_OBJECT
public:
explicit myClass(QObject *parent = nullptr): QObject(parent) {}
public slots:
void setTextProperty(const QString& s) {this->str = s;}
void getStrToQObj()
{
//TODO: set updated str into qml
}
signals:
void strChanged(const QString& time);
private:
QString str;
};
main.cpp
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
QQmlComponent component(&engine,
QUrl(QLatin1String("../myProj/qml/main.qml")));
QObject* item = component.create();
QObject* showTime = item->findChild<QObject*>("showTime");
QObject* butt = item->findChild<QObject*>("start");
myClass mc(item);
QObject::connect(butt, SIGNAL(buttClick(QString)),
&mc, SLOT(setTextProperty(QString)));
return app.exec();
}
Connection of Qml signal buttClick to setTextProperty(const QString& s) works fine and myClass::str is changed.The question is how to connect Text property _textField to update every time, when myClass::str is changed?

Answer 1

Do not export objects from QML to C++, instead do the opposite: export the C ++ objects to QML since this way the connection is simple and there is no need to use the old connection syntax:
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
myClass mc;
engine.rootContext()->setContextProperty("mc", &mc);
QQmlComponent component(&engine,
QUrl(QLatin1String("../myProj/qml/main.qml")));
QObject* item = component.create();
return app.exec();
}
Rectangle {
Text {
id: text1
text: "passive"
}
Button {
id: _button
anchors.top: text1.bottom
text: "Button"
onClicked: {
mc.setTextProperty("state: active");
}
}
Connections {
function onTimeChanged(text) {
text1.text = text;
}
target: mc
}
}

Answer 2

It is old syntax of connection, but according to separations logiv from GUI, and for ones who do not know JS well,turns out you can call parent() method to you class because it is inherit QObject class. This return to you Qobject* you put in constructor of your class, and then you can findChild and work with it:
void myClass::f(){
//do fancy stuff with your myClass::str
emit activityChanged(this->parent())
}
void getStrToQObj(QObject* qo)
{
auto tmp = qo->findChild<QObject*>("showTime");
tmp->setProperty("_textField", this->str);
}
And connect this in main.cpp like:
QObject::connect(&mc, SIGNAL(strChanged(QObject*)),
&mc, SLOT(getStrToQObj(QObject*)));