[Interest] 64-bit internal ID for QModelIndex?

[Nikos Chantziaras]

On 21/08/12 23:55, Stephen Chu wrote:
> On 8/21/12 4:26 PM, Nikos Chantziaras wrote:
>> On 21/08/12 22:45, Stephen Chu wrote:
>>> On 8/21/12 3:35 PM, Christoph Feck wrote:
>>>> On Tuesday 21 August 2012 20:55:00 Stephen Chu wrote:
>>>>> Is there a way to store a 64-bit internal ID in QModelIndex? The
>>>>> function QModelIndex::internalId() returns a 64-bit number but
>>>>> there's no way to put one in. The constructor takes only a 32-bit
>>>>> integer.
>>>>
>>>> Try using the overload that takes the void * pointer. The return value
>>>> is 64 bit, because pointers can also be 64 bit, and C++ doesn't allow
>>>> different overloads with different return values.
>>>
>>> Thanks for the help. But my app is currently 32-bit. :(
>>
>> Would a pointer to a qint64 work?
>
> Yes, it will. I was thinking about that but got stuck trying to figuring
> out how I can manage the memory since QModelIndedx does not own the
> object/memory pointed by the void*
>
> Say I allocate a QList<int64_t> and create indices with internal pointer
> pointing to elements in the list. When I need to update the model from
> external data, I will have to re-allocate the list and the existing
> pointers will be left dangling. What is the proper steps to update the
> model data in this case?

Note that I didn't work with QAbstractItemModel before, so perhaps I'm 
not the most suitable person here to give advice.  With that being said, 
you might be able to allocate like this:

   createIndex(row, column, new qint64(value));

Access the value with:

   *(qint64*)internalPointer();

And when you don't need the QModelIndex anymore, you deallocate like this:

   delete (qint64*)internalPointer();

You should probably create wrappers for those operations.  Or work out a 
subclass model.

But again, I didn't work with that part of Qt before, so I might be 
talking gibberish here ;-)