Hi,

I have a tree model:

A
|_AA
| |_id1 a b c d e f
| |_id2 e r t y i j
| |_id3 t f g h s w
| |_id4 l o m n h k
| |_id5 a b c d e f
| |_id6 a b c d e f
| |_id7 a b c d e f
| |_id8 a b c d e f

and I'd like to display it in the tree view as the following arrangement:

A
|_AA
| |_id1 id2 id3 id4
| |_id5 id6 id7 id8

Mapping algorithm would be:
if index has children then pass index otherwise map row to row/4, column to column%4 and don't display indices with column > 0.

I've reimplemented mapToSource, mapFromSource, filterAcceptsColumn:

Qt Code: 
  1. bool MyProxyModel::filterAcceptsColumn(int sourceColumn, const QModelIndex &sourceParent) const
  2. {
  3.     return ( sourceParent.isValid() || 
  4.             sourceParent.child(0,0).isValid() || 
  5.             ( !sourceParent.child(0,0).isValid() && sourceColumn==0 )
  6.             );
  7. } 
  8.  
  9. QModelIndex MyProxyModel::mapFromSource( const QModelIndex & sourceIndex ) const
  10. {
  11.     if(sourceIndex.isValid()) {
  12.         if( sourceIndex.child(0,0).isValid() ) {
  13.             return sourceIndex;
  14.         } else {
  15.             if( sourceIndex.column() == 0 ) {
  16.                 return createIndex(sourceIndex.row()/4, sourceIndex.row()%4);
  17.             } else {
  18.                 return QModelIndex();
  19.             }
  20.         }
  21.     } else {
  22.         return QModelIndex();
  23.     }
  24. }
  25.  
  26.  
  27. QModelIndex MyProxyModel::mapToSource ( const QModelIndex & proxyIndex ) const
  28. {
  29.     if(proxyIndex.isValid()) {
  30.         QStandardItem *item = (QStandardItem *) proxyIndex.internalPointer();
  31.         if( item!=0 && item->hasChildren() ) {
  32.             return proxyIndex;
  33.         } else {
  34.             return sourceModel()->index(
  35.                 proxyIndex.row()*4 + proxyIndex.column(),
  36.                 0,
  37.                 proxyIndex.parent()
  38.                 );
  39.         }
  40.     } else {
  41.         return QModelIndex();
  42.     }
  43. }
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I'm crashing while clicking on AA and trying to expand it.
( QTreeViewPrivate::layout(int i); line 3130 Q_Assert(i>-1) )

I'd appreciate ideas on how to approach this issue.

Cheers,
Wojtek