Proper way to binding QML Controls and C++ model

fromis_9

Hi. I wonder what is the best way binding QML control type and C++ model.

// My C++ model
class Backend : public QObject {
Q_OBJECT
  Q_PROPERTY(bool myCheck READ myCheck WRITE SetMyCheck NOTIFY myCheckChanged)
// ...
}

// QML binding
CheckBox {
  id: qmlCheckBox
  checked: backend.myCheck
  onCheckedChanged: backend.myCheck = checked
}

Like above, when C++ model(@myCheck) is changed in C++ code, then it should be notified to QML so that @qmlCheckBox is also changed.
Changing in QML also should change C++ model. (vice versa)
But there was a binding loop detected warnings.
I KNOW WHY THERE IS BINDING LOOP. I wonder how to do what I want without binding loop.
Thanks.

GrecKo

@fromis_9 Controls usually provide a signal to indicate that a change has come from a user interaction signal, you should use this one instead of the "raw" <property>Changed signal that will fire both on backend and frontend changes.

For CheckBox it is the toggled signal, for ComboBox activated, for TextField textEdited, ...

So in your case it would be:

CheckBox {
  id: qmlCheckBox
  checked: backend.myCheck
  onToggled: backend.myCheck = checked
}

Make sure to also not emit the notify signal in the setter if the property doesn't actually changed, generally done with an if at the start:

void Backend::SetMyCheck(bool myCheck)
{
    if (myCheck == m_myCheck) 
        return;
    m_myCheck = myCheck;
    emit myCheckChanged();
}