kdelibs/kdeui/itemviews/kviewstatesaver.h

/*
    Copyright (C) 2010 Klarälvdalens Datakonsult AB,
        a KDAB Group company, info@kdab.net,
        author Stephen Kelly <stephen@kdab.com>

    This library is free software; you can redistribute it and/or modify it
    under the terms of the GNU Library General Public License as published by
    the Free Software Foundation; either version 2 of the License, or (at your
    option) any later version.

    This library is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
    License for more details.

    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to the
    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
    02110-1301, USA.
*/

#ifndef KVIEWSTATESAVER_H
#define KVIEWSTATESAVER_H

#include <QtCore/QObject>
#include <QtCore/QPair>

#include "kdeui_export.h"

#include <QAbstractItemView>
#include <QItemSelectionModel>
#include <QAbstractItemModel>
#include <QAbstractScrollArea>
#include <QModelIndex>
#include <QStringList>

class KConfigGroup;

class KViewStateSaverPrivate;

/**
  @brief Object for saving and restoring state in QTreeViews and QItemSelectionModels

  Implement the indexFromConfigString and indexToConfigString methods to
  handle the model in the view whose state is being saved. These implementations can be quite trivial:

  @code
    QModelIndex DynamicTreeStateSaver::indexFromConfigString(const QAbstractItemModel* model, const QString& key) const
    {
      QModelIndexList list = model->match(model->index(0, 0), DynamicTreeModel::DynamicTreeModelId, key.toInt(), 1, Qt::MatchRecursive);
      if (list.isEmpty())
        return QModelIndex();
      return list.first();
    }

    QString DynamicTreeStateSaver::indexToConfigString(const QModelIndex& index) const
    {
      return index.data(DynamicTreeModel::DynamicTreeModelId).toString();
    }
  @endcode

  It is possible to restore the state of a QTreeView (that is, the expanded state and selected state of all indexes
  as well as the horizontal and vertical scroll state) by using setTreeView.

  If there is no tree view state to restore (for example if using QML), the selection state of a QItemSelectionModel
  can be saved or restored instead.

  The state of any QAbstractScrollArea can also be saved and restored.

  A KViewStateSaver should be created on the stack when saving and on the heap when restoring. The model may be populated dynamically between several
  event loops, so it may not be immediate for the indexes that should be selected to be in the model. The saver should *not* be persisted as a
  member. The saver will destroy itself when it has completed the restoration specified in the config group, or a small amount of time has elapsed.

  @code
    MyWidget::MyWidget(Qobject *parent)
      : QWidget(parent)
    {
      ...

      m_view = new QTreeView(splitter);
      m_view->setModel(model);

      connect( model, SIGNAL(modelAboutToBeReset()), SLOT(saveState()) );
      connect( model, SIGNAL(modelReset()), SLOT(restoreState()) );
      connect( qApp, SIGNAL(aboutToQuit()), SLOT(saveState()) );

      restoreState();
    }

    void StateSaverWidget::saveState()
    {
      ConcreteStateSaver saver;
      saver.setTreeView(m_view);

      KConfigGroup cfg( KGlobal::config(), "ExampleViewState" );
      saver.saveState( cfg );
      cfg.sync();
    }

    void StateSaverWidget::restoreState()
    {
      // Will delete itself.
      ConcreteTreeStateSaver *saver = new ConcreteStateSaver();
      saver->setTreeView(m_view);
      KConfigGroup cfg( KGlobal::config(), "ExampleViewState" );
      saver->restoreState( cfg );
    }
  @endcode

  After creating a saver, the state can be saved using a KConfigGroup.

  It is also possible to save and restore state directly by using the restoreSelection,
  restoreExpanded etc methods. Note that the implementation of these methods should return
  strings that the indexFromConfigString implementation can handle.

  @code
    class DynamicTreeStateSaver : public KViewStateSaver
    {
      Q_OBJECT
    public:
      // ...

      void selectItems(const QList<qint64> &items)
      {
        QStringList itemStrings;
        foreach(qint64 item, items)
          itemStrings << QString::number(item);
        restoreSelection(itemStrings);
      }

      void expandItems(const QList<qint64> &items)
      {
        QStringList itemStrings;
        foreach(qint64 item, items)
          itemStrings << QString::number(item);
        restoreSelection(itemStrings);
      }

    };
  @endcode


  Note that a single instance of this class should be used with only one widget. That is don't do this:

  @code
    saver->setTreeView(treeView1);
    saver->setSelectionModel(treeView2->selectionModel());
    saver->setScrollArea(treeView3);
  @endcode

  To save the state of 3 different widgets, use three savers, even if they operate on the same root model.

  @code
    saver1->setTreeView(treeView1);
    saver2->setSelectionModel(treeView2->selectionModel());
    saver3->setScrollArea(treeView3);
  @endcode

  @note The KViewStateSaver does not take ownership of any widgets set on it.

  It is recommended to restore the state on application startup and after the model has been reset, and to
  save the state on application close and before the model has been reset.

  @see QAbstractItemModel::modelAboutToBeReset QAbstractItemModel::modelReset

  @author Stephen Kelly <stephen@kdab.com>
  @since 4.5
*/
class KDEUI_EXPORT KViewStateSaver : public QObject
{
  Q_OBJECT
public:
  /**
    Constructor
    @param parent standard parent object, but ignored since this object will delete itself
  */
  explicit KViewStateSaver(QObject *parent = 0);

  /**
    Destructor
  */
  ~KViewStateSaver();

  /**
   * The view whose state is persisted.
   */
  QAbstractItemView* view() const;

  /**
   * Sets the view whose state is persisted.
   */
  void setView(QAbstractItemView *view);

  /**
    The QItemSelectionModel whose state is persisted.
  */
  QItemSelectionModel* selectionModel() const;

  /**
    Sets the QItemSelectionModel whose state is persisted.
  */
  void setSelectionModel( QItemSelectionModel *selectionModel );

  /**
    Saves the state to the @p configGroup
  */
  void saveState(KConfigGroup &configGroup);

  /**
    Restores the state from the @p configGroup
  */
  void restoreState(const KConfigGroup &configGroup);

  /**
   * Returns a QStringList describing the selection in the selectionModel.
   */
  QStringList selectionKeys() const;

  /**
   * Returns a QStringList representing the expanded indexes in the QTreeView.
   */
  QStringList expansionKeys() const;

  /**
   * Returns a QString describing the current index in the selection model.
   */
  QString currentIndexKey() const;

  /**
   * Returns the vertical and horizontal scroll of the QAbstractScrollArea.
   */
  QPair<int, int> scrollState() const;

  /**
   * Select the indexes described by @p indexStrings
   */
  void restoreSelection( const QStringList &indexStrings );

  /**
   * Make the index described by @p indexString the currentIndex in the selectionModel.
   */
  void restoreCurrentItem( const QString &indexString );

  /**
   * Expand the indexes described by @p indexStrings in the QTreeView.
   */
  void restoreExpanded( const QStringList &indexStrings );

  /**
   * Restores the scroll state of the QAbstractScrollArea to the @p verticalScoll
   * and @p horizontalScroll
   */
  void restoreScrollState( int verticalScoll, int horizontalScroll );

protected:
  /**
    Reimplement to return an index in the @p model described by the unique key @p key
  */
  virtual QModelIndex indexFromConfigString(const QAbstractItemModel *model, const QString &key) const = 0;

  /**
    Reimplement to return a unique string for the @p index.
  */
  virtual QString indexToConfigString(const QModelIndex &index) const = 0;

private:
  //@cond PRIVATE
  Q_DECLARE_PRIVATE(KViewStateSaver)
  KViewStateSaverPrivate * const d_ptr;
  Q_PRIVATE_SLOT( d_func(), void rowsInserted( const QModelIndex&, int, int ) )
  Q_PRIVATE_SLOT( d_func(), void restoreScrollBarState() )
  //@endcond
};

#endif