Proxy model example code

Related to "this FAQ entry":http://developer.qt.nokia.com/faq/answer/how_can_i_implement_my_own_proxy_model_that_is_more_advanced_than_just_sort.

#include <QtGui>

QList<QStandardItem *> list;

class SortProxy : public QAbstractProxyModel
{
 Q_OBJECT

public:
 SortProxy(QObject *parent = 0) : QAbstractProxyModel(parent), hideThem(false)
 {
 fixModel();
 }

int rowCount(const QModelIndex &amp;parent) const
 {
 QModelIndex sourceParent;
 if (parent.isValid())
 sourceParent = mapToSource(parent);
 int count = 0;
 QMapIterator<QPersistentModelIndex, QPersistentModelIndex> it(proxySourceParent);
 while (it.hasNext()) {
 it.next();
 if (it.value() == sourceParent)
 count++;
 }
 return count;
 }

int columnCount(const QModelIndex &amp;) const
 {
 return 1;
 }

QModelIndex index(int row, int column, const QModelIndex &amp;parent = QModelIndex()) const
 {
 QModelIndex sourceParent;
 if (parent.isValid())
 sourceParent = mapToSource(parent);
 QMapIterator<QPersistentModelIndex, QPersistentModelIndex> it(proxySourceParent);
 while (it.hasNext()) {
 it.next();
 if (it.value()  sourceParent &amp;amp;&amp;amp; it.key().row()  row &amp;&amp;
 it.key().column() == column)
 return it.key();
 }
 return QModelIndex();
 }

QModelIndex parent(const QModelIndex &amp;child) const
 {
 QModelIndex mi = proxySourceParent.value(child);
 if (mi.isValid())
 return mapFromSource(mi);
 return QModelIndex();
 }

QModelIndex mapToSource(const QModelIndex &amp;proxyIndex) const
 {
 if (!proxyIndex.isValid())
 return QModelIndex();
 return mapping.key(proxyIndex);
 }

QModelIndex mapFromSource(const QModelIndex &amp;sourceIndex) const
 {
 if (!sourceIndex.isValid())
 return QModelIndex();
 return mapping.value(sourceIndex);
 }

public slots:
 void hideEverythingButA1AndChildren()
 {
 hideThem = !hideThem;
 // Now we set up the proxy <-> source mappings
 emit layoutAboutToBeChanged();
 fixModel();
 emit layoutChanged();
 }

private:
 void fixModel()
 {
 mapping.clear();
 proxySourceParent.clear();
 for (int i=0;i<list.size();i+'') {
 QStandardItem *si = list.at(i);
 if (hideThem) {
 if (!si->text().startsWith("A") || !si->parent())
 continue;
 QModelIndex proxy = createIndex(si->row(), si->column(), si->index().internalPointer());
 mapping.insert(QPersistentModelIndex(si->index()), proxy);
 QModelIndex sourceParent;
 if (si->parent()->parent())
 sourceParent = si->parent()->index();
 proxySourceParent.insert(proxy, sourceParent);
 } else {
 QModelIndex proxy = createIndex(si->row(), si->column(), si->index().internalPointer());
 mapping.insert(QPersistentModelIndex(si->index()), proxy);
 QModelIndex sourceParent;
 if (si->parent())
 sourceParent = si->parent()->index();
 proxySourceParent.insert(proxy, sourceParent);
 }
 }
 }
 QMap<QPersistentModelIndex, QPersistentModelIndex> mapping;
 QMap<QPersistentModelIndex, QPersistentModelIndex> proxySourceParent;
 bool hideThem;
};

SortProxy *proxyModel = 0;

class Tree : public QTreeView
{
 Q_OBJECT

public:
 Tree(QWidget *parent = 0) : QTreeView(parent)
 {
 QStandardItemModel *sourceModel = new QStandardItemModel(this);

 QStandardItem *parentA = sourceModel->invisibleRootItem();
 for (int i = 0; i < 2;i) {
 itemA = new QStandardItem(QString("A %0").arg(i));
 parentA->appendRow(itemA);
 parentA = itemA;
 list.append(itemA);
 }
 itemA = new QStandardItem(QString("A 2"));
 parentA->appendRow(itemA);
 list.append(itemA);
 itemA3 = new QStandardItem(QString("A 3"));
 list.append(itemA3);
 parentA->appendRow(itemA3);
 itemA4 = new QStandardItem(QString("A 4"));
 list.append(itemA4);
 parentA->appendRow(itemA4);
 itemNonA = new QStandardItem(QString("Non A"));
 list.append(itemNonA);
 parentA->appendRow(itemNonA);

 QStandardItem *parentB = sourceModel->invisibleRootItem();
 for (int i = 0; i < 3;i) {
 itemB = new QStandardItem(QString("B %0").arg(i));
 parentB->appendRow(itemB);
 parentB = itemB;
 list.append(itemB);
 }

 QStandardItem *parentC = sourceModel->invisibleRootItem();
 for (int i = 0; i < 3;i) {
 itemC = new QStandardItem(QString("C %0").arg(i));
 parentC->appendRow(itemC);
 parentC = itemC;
 list.append(itemC);

 }

 proxyModel = new SortProxy(this);
 proxyModel->setSourceModel(sourceModel);
 setModel(proxyModel);
 expandAll();
 }
 QStandardItem *itemA;
 QStandardItem *itemA3;
 QStandardItem *itemA4;
 QStandardItem *itemNonA;
 QStandardItem *itemB;
 QStandardItem '''itemC;
};


#include "main.moc"

int main(int argc, char'''*argv)
{
 QApplication app(argc, argv);
 QWidget widget;
 QPushButton *button = new QPushButton("Make only A1'' 'A' children visible", &amp;widget);
 Tree *tree = new Tree(&amp;widget);
 QVBoxLayout *lay = new QVBoxLayout(&amp;widget);
 lay->addWidget(button);
 QObject::connect(button, SIGNAL (clicked()), proxyModel, SLOT (hideEverythingButA1AndChildren()));
 lay->addWidget(tree);
 widget.show();
 return app.exec();
}