Synchronizing behaviour between QListView and QGraphicsScene

**russdot** · 26th April 2012, 23:49

But if you think about the idea of using a 2-way map between QStandardItem and QGraphicsItem, the synchronization problem is resolved pretty easily. When the user selects items from the tree, you retrieve the list of selected QStandardItems, look them up in the map, and set the matching QGraphicsItem to selected. Likewise, when the user selects items in the graphics view, you do the reverse lookup and set the QStandardItem as selected.

Exactly. The solution I came up with is a templated bi-directional hash map:

Qt Code:

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template <class U, class V>
class BidirectionalHashMap
{
public:
    U find(V v) { return mapVU.find(v).value(); }
    V find(U u) { return mapUV.find(u).value(); }
    void insert(U u, V v) { mapUV.insert(u,v); mapVU.insert(v,u); }
 
private:
    QHash<U, V> mapUV;
    QHash<V, U> mapVU;
};

template <class U, class V>
class BidirectionalHashMap
{
public:
    U find(V v) { return mapVU.find(v).value(); }
    V find(U u) { return mapUV.find(u).value(); }
    void insert(U u, V v) { mapUV.insert(u,v); mapVU.insert(v,u); }

private:
    QHash<U, V> mapUV;
    QHash<V, U> mapVU;
};

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It works great for what I needed to accomplish.

**d_stranz** · 27th April 2012, 04:56

It works great for what I needed to accomplish.

At least as long as either of the QHash::find() calls in your two find() methods doesn't return QHash::end(). Then the following call to QHash::iterator::value() will assert. If your code guarantees that you will never try to find() a key that isn't in the map, this won't be a problem.