/// <summary>
    /// Extended OxyPlot ColumnItem class.  Adds a label, which is used by elements such
    /// as a category axis.
    /// </summary>
    public class Item : ColumnItem, INotifyPropertyChanged
    {
        /// <summary>
        /// Label field.  May be used for category axis.
        /// </summary>
        private string _label;

        /// <summary>
        /// Label property.  May be used for category axis.
        /// </summary>
        public string Label
        {
            get { return _label; }
            set
            {
                if (_label != value)
                {
                    _label = value;
                    NotifyPropertyChanged();
                }
            }
        }

        /// <summary>
        /// PropertyChanged event handler.
        /// </summary>
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// PropertyChanged event handling method.
        /// </summary>
        /// <param name="propertyName">Property name.  If not passed, name of the property, 
        /// which called this method, is used.</param>
        private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }

    /// <summary>
    /// Extended OxyPlot ColumnSeries class.  Allows selection of columns and tracks which 
    /// column has been selected.
    /// </summary>
    public class SelectableColumnSeries : ColumnSeries, INotifyPropertyChanged
    {    
        /// <summary>
        /// Selected ColumnItem field.
        /// </summary>
        private ColumnItem _selectedColumn;

        /// <summary>
        /// Selected ColumnItem property.
        /// </summary>
        public ColumnItem SelectedColumn
        {
            get { return _selectedColumn; }
            set
            {
                if (_selectedColumn != value)
                {
                    _selectedColumn = value;
                    NotifyPropertyChanged();
                }
            }
        }

        /// <summary>
        /// Selected ColumnItem color field.
        /// </summary>
        private OxyColor _selectedColumnColor;

        /// <summary>
        /// Selected ColumnItem color property.
        /// </summary>
        public OxyColor SelectedColumnColor
        {
            get { return _selectedColumnColor; }
            set
            {
                _selectedColumnColor = value;
                NotifyPropertyChanged();
            }
        }

        /// <summary>
        /// SelectableColumnSeries constructor.
        /// </summary>
        public SelectableColumnSeries()
        {
            MouseDown += SelectableColumnSeries_MouseDown;
        }

        /// <summary>
        /// MouseDown event handler for the SelectableColumnSeries.  Handles changing of the selected 
        /// ColumnItem, as well as its color, if a SelectedColumnColor was provided.  If the color for 
        /// selection was not provided, then no visual feedback is provided, but the selection is still 
        /// made.
        /// </summary>
        /// <param name="sender">Event sender (object).</param>
        /// <param name="e">Event arguments (OxyMouseDownEventArgs).</param>
        protected void SelectableColumnSeries_MouseDown(object sender, OxyMouseDownEventArgs e)
        {
            var nearest = GetNearestPoint(e.Position, false);
            var column = nearest.Item as ColumnItem;
            if (column == null)
            {
                return;
            }

            if (SelectedColumn != null)
            {
                SelectedColumn.Color = FillColor;
            }

            if (!SelectedColumnColor.IsUndefined())
            {
                column.Color = SelectedColumnColor;
            }

            SelectedColumn = column;
            PlotModel.InvalidatePlot(true);
        }

        /// <summary>
        /// PropertyChanged event handler.
        /// </summary>
        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// PropertyChanged event handling method.
        /// </summary>
        /// <param name="propertyName">Property name.  If not passed, name of the property, 
        /// which called this method, is used.</param>
        private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }