ValueWriteBack.hpp

#pragma once
 
// Writes a port's value back into its bound QML property without clobbering an
// in-progress edit. Two guards: equality, since the value is usually the echo of
// the UI's own write; and focus, because avnd republishes every control input of
// a process when any one changes, so the snapshot can lag a keystroke that has
// not reached the executor yet. A value suppressed by the focus guard is dropped
// rather than replayed, being older than what the port already holds.
 
#include <QMetaType>
#include <QObject>
#include <QQmlProperty>
#include <QVariant>
 
namespace JS
{
 
inline bool targetHasActiveFocus(const QQmlProperty& prop) noexcept
{
  auto* obj = prop.object();
  if(!obj)
    return false;
 
  const QVariant focus = obj->property("activeFocus");
  return focus.typeId() == QMetaType::Bool && focus.toBool();
}
 
 
inline bool writeBackUnlessEditing(QQmlProperty& prop, const QVariant& value)
{
  if(!prop.isValid())
    return false;
 
  // Qt 6 compares numbers across int / float / double here, so a float port
  // echoing into a `real` property does not count as a change.
  if(prop.read() == value)
    return false;
 
  if(targetHasActiveFocus(prop))
    return false;
 
  prop.write(value);
  return true;
}
 
}