[umbrello] [Bug 445119] Issues with code ignoring and possibly dereferencing nullptr

[Robert Hairgrove]

https://bugs.kde.org/show_bug.cgi?id=445119

--- Comment #3 from Robert Hairgrove <code at roberthairgrove.com> ---
I realize now, after looking through the source code and docs for QList and
QPointer, that this would not work with signals and slots unless a completely
different copying mechanism and/or redesign of UMLObjectList were implemented.
Neither QList nor QPointer are descendents of QObject, so they emit no signals.
UMLObjectList would most likely have to contain a QList<QPointer<UMLObject>>
member instead of inheriting it directly. Read and write operations could be
forwarded directly to the QList member, but adding and removing objects
(pointers) should be controlled by UMLObjectList.

What I can envision now, without knowing all of the details about how this
class is used, is the following:

1. Class UMLObjectList should inherit from QObject, or possibly just implement
signals and slots using the Q_OBJECT macro;
2. UMLObjectList should connect itself via slot to the "destroyed()" signal of
each element added to its list which should only be permitted through its own
"append()" function (and removal through a correlated "remove()" function);
3. Whenever a contained element is destroyed, the slot would have to find the
pointer in its list and then remove it. Of course, the actual object deletion
would be left to QPointer.

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