Doc - Adding Pierre Rossi's frozen column example

Reviewed-By: TrustMe

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+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: Qt Software Information (qt-info@nokia.com)
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+****************************************************************************/
+
+/*!
+    \example itemviews/frozencolumn
+    \title Frozen Column Example
+
+    This example demonstrates how to freeze a column within a QTableView.
+
+    \image frozencolumn-example.png "Screenshot of the example"
+
+    We use Qt's model/view framework to implement a table with its first
+    column frozen. This technique can be aplied to several columns or rows,
+    as long as they are on the edge of the table.
+
+    The model/view framework allows for one model to be displayed in different
+    ways using multiple views. For this example, we use two views on the same
+    model - two \l {QTableView}{table views} sharing one model. The frozen
+    column is a child of the main tableview, and we provide the desired visual
+    effect using an overlay technique which will be described step by step in
+    the coming sections.
+
+    \image frozencolumn-tableview.png
+
+
+    \section1 FreezeTableWidget Class Definition
+
+    The \c FreezeTableWidget class has a constructor and a destructor. Also, it
+    has two private members: the table view that we will use as an overlay, and
+    the shared model for both table views. Two slots are added to help keep the
+    section sizes in sync, as well as a function to readjust the frozen
+    column's geometry. In addition, we reimplement two functions:
+    \l{QAbstractItemView::}{resizeEvent()} and \l{QTableView::}{moveCursor()}.
+
+    \snippet examples/itemviews/frozencolumn/freezetablewidget.h Widget definition
+
+    \note QAbstractItemView is \l{QTableView}'s ancestor.
+
+
+    \section1 FreezeTableWidget Class Implementation
+
+    The constructor takes \a model as an argument and creates a table view that
+    we will use to display the frozen column. Then, within the constructor, we
+    invoke the \c init() function to set up the frozen column. Finally, we
+    connect the \l{QHeaderView::sectionResized()} signals (for horizontal and
+    vertical headers) to the appropriate slots. This ensures that our frozen
+    column's sections are in sync with the headers. We also connect the
+    vertical scrollbars together so that the frozen column scrolls vertically
+    with the rest of our table.
+
+    \snippet examples/itemviews/frozencolumn/freezetablewidget.cpp constructor
+
+
+    In the \c init() function, we ensure that the overlay table view
+    responsible for displaying the frozen column, is set up properly. This
+    means that this table view, \c frozenTableView, has to have the same model
+    as the main table view. However, the difference here is: \c frozenTableView's
+    only visible column is its first column; we hide the others using
+    \l{QTableView::}{setColumnHidden()}
+
+    \snippet examples/itemviews/frozencolumn/freezetablewidget.cpp init part1
+
+
+    In terms of the frozen column's z-order, we stack it on top of the
+    viewport. This is achieved by calling \l{QWidget::}{stackUnder()} on the
+    viewport. For appearance's sake, we prevent the column from stealing focus
+    from the main tableview. Also, we make sure that both views share the same
+    selection model, so only one cell can be selected at a time. A few other
+    tweaks are done to make our application look good and behave consistently
+    with the main tableview. Note that we called \c updateFrozenTableGeometry()
+    to make the column occupy the correct spot.
+
+    \snippet examples/itemviews/frozencolumn/freezetablewidget.cpp init part2
+
+    When you resize the frozen column, the same column on the main table view
+    must resize accordingly, to provide seamless integration. This is
+    accomplished by getting the new size of the column from the \c newSize
+    value from the \l{QHeaderView::}{sectionResized()} signal, emitted by both
+    the horizontal and vertical header.
+
+    \snippet examples/itemviews/frozencolumn/freezetablewidget.cpp sections
+
+    Since the width of the frozen column is modified, we adjust the geometry of
+    the widget accordingly by invoking \c updateFrozenTableGeometry(). This
+    function is further explained below.
+
+    In our reimplementation of QTableView::resizeEvent(), we call
+    \c updateFrozenTableGeometry() after invoking the base class
+    implementation.
+
+    \snippet examples/itemviews/frozencolumn/freezetablewidget.cpp resize
+
+    When navigating around the table with the keyboard, we need to ensure that
+    the current selection does not disappear behind the frozen column. To
+    synchronize this, we reimplement QTableView::moveCursor() and adjust the
+    scrollbar positions if needed, after calling the base class implementation.
+
+    \snippet examples/itemviews/frozencolumn/freezetablewidget.cpp navigate
+
+    The frozen column's geometry calculation is based on the geometry of the
+    table underneath, so it always appears in the right place. Using the
+    QFrame::frameWidth() function helps to calculate this geometry correctly,
+    no matter which style is used. We rely on the geometry of the viewport and
+    headers to set the boundaries for the frozen column.
+
+    \snippet examples/itemviews/frozencolumn/freezetablewidget.cpp geometry
+
+*/
+