Qt Model View Programming: Creating indexes

Question

I am reading through following documentation to increase my understanding of model-view programming:

http://qt-project.org/doc/qt-4.8/model-view-programming.html

Although its nicely written, I have a question regarding creating indexes. As far as I understand to calculate and item's index we need index of its parent item. To calculate index of the parent item we need index of child item. So its a circular dependency. How do you break it?

If you go through following section:

Rows and columns

The diagram shows a representation of a basic table model in which each item is located by a pair of row and column numbers. We obtain a model index that refers to an item of data by passing the relevant row and column numbers to the model.

 QModelIndex indexA = model->index(0, 0, QModelIndex());
 QModelIndex indexB = model->index(1, 1, QModelIndex());
 QModelIndex indexC = model->index(2, 1, QModelIndex());

Top level items in a model are always referenced by specifying QModelIndex() as their parent item. This is discussed in the next section.

I do not understand how does Qt know to calculate index of A, parent index should be QModelIndex() (i.e. the index of top level item).

"how does Qt know to calculate index of A, parent index should be QModelIndex()" It is. — cmannett85

cmannett85 cmannett85 · Accepted Answer · 2013-03-08T08:22:13

As far as I understand to calculate and item's index we need index of its parent item.

Yes, unless it is a top level item.

To calculate index of the parent item we need index of child item.

No. An index cannot have more than one parent, so just call QModelIndex::parent() const.

Qt Model View Programming: Creating indexes

1 Answers