Question

I’ve a tree-like polymorphic data-structure, where the nodes are instances of class Node (implemented by me) or any its subclass. My application heavily uses Boost and the nodes are actually represented by boost::shared_ptr type rather than Node*.

Now, I want to create a Qt model to wrap my tree data-structure. Therefore I need a way to associate any model index with a node in my internal data structure. And here comes the problem:

Qt supports two ways of doing it:

First:

QModelIndex QAbstractItemModel::createIndex ( int row, int column, void * ptr = 0 ) const

Creates a model index for the given
row and column with the internal
pointer ptr.

And second:

QModelIndex QAbstractItemModel::createIndex ( int row, int column, quint32 id ) const

Creates a model index for the given
row and column with the internal
identifier, id.

Ok, and how exactly should I associate the node in my case? There is no possibility to associate a shared_ptr with the model index… Yes, I know, I can receive a raw pointer from my shared_ptr and supply it to CreateIndex(), but it smells bad – seems too unsafe to me.

Any ideas?

By the way, I feel that in general Boost / Qt integration seems to be not trivial at least in the area of memory management.

10x a lot.

Answer 1

If you want to do an easy association without passing a raw pointer, put the shared memory in a container and pass the ID value for that container element into the model index. For example, you could created declare

QMap< quint32, boost::shared_ptr< Foo > > index_map;

and use that. You’d have to be careful to not duplicate IDs for existing pointers, perhaps. It seems somewhat overly complicated to me….

You could also just keep a list of the pointers (to ensure continued availability as you need them) and then use the actual address of the pointer in the QModelIndex as well. This is probably what I would do.