View source for Proxy model example code

{{Cleanup | reason=Auto-imported from ExpressionEngine.}}

[[Category:snippets]]
[[Category:HowTo]]
[[Category:Developing with Qt]]

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

<pre>
#include <QTreeView>
#include <QPushButton>
#include <QVBoxLayout>
#include <QStandardItem>
#include <QApplication>
#include <QAbstractProxyModel>
 
QList<QStandardItem *> list;
 
class SortProxy : public QAbstractProxyModel
{
    Q_OBJECT
 
public:
    SortProxy(QObject *parent = 0) : QAbstractProxyModel(parent), hideThem(false)
    {
        fixModel();
    }
 
    int rowCount(const QModelIndex &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 &) const
    {
        return 1;
    }
 
    QModelIndex index(int row, int column, const QModelIndex &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 && it.key().row() == row &&
                it.key().column() == column)
                return it.key();
        }
        return QModelIndex();
    }
 
    QModelIndex parent(const QModelIndex &child) const
    {
        QModelIndex mi = proxySourceParent.value(child);
        if (mi.isValid())
            return mapFromSource(mi);
        return QModelIndex();
    }
 
    QModelIndex mapToSource(const QModelIndex &proxyIndex) const
    {
        if (!proxyIndex.isValid())
            return QModelIndex();
        return mapping.key(proxyIndex);
    }
 
    QModelIndex mapFromSource(const QModelIndex &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();
 
        //the following list is already populated
        //in the tree view and we shall browse and
        //customize it here
        for (int i=0;i<list.size();i++)
        {
            //pull out a standard item
            QStandardItem *si = list.at(i);
 
            if (hideThem)
            {
                //if the hide item flag is true
 
                //check if the standard item's text start with 'A'
                //of the item is not parent
                if (!si->text().startsWith("A") || !si->parent())
                    continue;
 
 
                //means that we have encountered item that does not start with 'A'
                //or the item is not the parent
 
                //we pull out the model index by creating the model index with the source items
                //row , column
                QModelIndex proxy = createIndex(si->row(), si->column(), si->index().internalPointer());
 
                //insert the source model's index and the proxy index into the map
                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", &widget);
    Tree *tree = new Tree(&widget);
    QVBoxLayout *lay = new QVBoxLayout(&widget);
    lay->addWidget(button);
    QObject::connect(button, SIGNAL(clicked()), proxyModel, SLOT(hideEverythingButA1AndChildren()));
    lay->addWidget(tree);
    widget.show();
    return app.exec();
}
</pre>