==================================================================
The problem:
OriginGroupExtension::OriginGroupExtension () {
initExtensionType(OriginGroupExtension::getExtensionClassTypeId());
EXTENSION_ADD_PROPERTY_TYPE ( Origin, (0), 0, App::Prop_Hidden, "Origin linked to the group" );
}
initializes the Origin property to null.
Then Document::Restore => readObjects => addObject => slotNewObject => ViewProviderDocumentObject::updateView => ViewProviderBody::updateData => ViewProviderGeometryObject::updateData =>
ViewProviderDocumentObject::updateData => ViewProvider::updateData => ViewProviderOriginGroupExtension::extensionUpdateData => updateOriginSize() => OriginGroupExtension::getOrigin,
the latter throws an exception because the origin property is null.
Afterwards, the origin property is initialized during Document::Restore => readObjects => ExtensionContainer::Restore() => PropertyContainer::Restore() => App::PropertyLink::Restore()
=> App::PropertyLink::setValue() => Property::hasSetValue, which triggers an onChange: Body::onChanged => BodyBase::onChanged => Feature::onChanged => DocumentObject::onChanged =>
Document::onChangedProperty => Document::slotChangedObject => ViewProviderOriginGroupExtension::slotChangedObjectGui => ViewProviderOriginGroupExtension::updateOriginSize =>
OriginGroupExtension::getOrigin,
now, the latter that is the same that was throwing the exception and generating the error message above, does not throw anymore because Origin has been initialized.
When creating a new object, isNew==true; whereas when loading a file, isNew==false. Therefore, when loading a file setupObject is not executed. SetupObject, effectively initializes
the extension via: Body::setupObject => DocumentObject::setupObject => OriginGroupExtension::onExtendedSetupObject.
DocumentObject * Document::addObject(const char* sType, const char* pObjectName, bool isNew)
{
[more code here]
// Call the object-specific initialization
if (!d->undoing && !d->rollback && isNew) {
pcObject->setupObject ();
}
[more code here]
As DocumentObject code is generic for all objects (workbenches), by design it was chosen to initialize the object only if new. Therefore a object or an extension of a object being restored,
between the addition (addObject) and the restoring of the properties, must by design expect it not to be initialized.
The solution:
Making use of the Restore flag at document level (the one at object level is not sufficient), no exception regarding the null property is reported during document restoring.
Ticket:
https://freecadweb.org/tracker/view.php?id=2530fixes#2530
=============================================================
Prior this commit, if a body has transparency (let's say 55%) and a new feature is added, the transparency is lost until you update it again in the body.
This prevents to actually see through while editing the feature (e.g. while setting the length of a pad) and is very annoying as the user
is required to go back to the body properties, where the old value (e.g. 55%) would still be there and change it to another value (56%) to effect it.
