经过QSortFilterProxyModel过滤后的数据怎么访问？
比如说，源Model中有500条数据，使用QSortFilterProxyModel过滤后，我怎么能够知道经过过滤后还剩余多少条数据？怎么才能访问过滤后的结果数据呢？
谢谢！
------解决思路----------------------
QModelIndex QSortFilterProxyModel::mapToSource ( const QModelIndex & proxyIndex ) const [virtual]
Reimplemented from QAbstractProxyModel::mapToSource().
Returns the source model index corresponding to the given proxyIndex from the sorting filter model.
QModelIndex QSortFilterProxyModel::mapFromSource ( const QModelIndex & sourceIndex ) const [virtual]
Reimplemented from QAbstractProxyModel::mapFromSource().
Returns the model index in the QSortFilterProxyModel given the sourceIndex from the source model.