JfreeChart limit the number of legend items displayed

Question

I'm in charge of maintaining an application which can draw graphs using JFreeChart. The application is written in Eclipse-RCP and SWT and use a ChartComposite to display the charts.

The ChartComposite has been partially overridden in order to customize contextual menus depending on the selection:

@Override
    public void createPartControl(Composite parent) {
    super.createPartControl(parent);

    chart = createChart(timeSeriesDataset);

    chartComposite = new MyChartComposite(this, parent, SWT.NONE, chart, true);
    chartComposite.setLayoutData(new GridData(GridData.FILL_BOTH));

    selectionProvider = new GenericObjectSelectionProvider();
    getSite().setSelectionProvider(selectionProvider);

    // add information to the status line:
    selectionProvider.addSelectionChangedListener(statusLineListener);

    addDropSupport();// add D'n D support for dropping TimeSeries 

}


protected JFreeChart createChart(TimeSeriesCollection ptimeSeriesDataset) {

        JFreeChart vChart = ChartFactory.createTimeSeriesChart(null, "time", "values", ptimeSeriesDataset, true,
                false, false);
        vChart.setBackgroundPaint(Color.white);

        XYPlot plot = vChart.getXYPlot();
        plot.setBackgroundPaint(Color.lightGray);
        plot.setDomainGridlinePaint(Color.white);
        plot.setRangeGridlinePaint(Color.white);
        // plot.setAxisOffset(new RectangleInsets(5.0, 5.0, 5.0, 5.0));
        plot.setDomainCrosshairVisible(true);
        plot.setRangeCrosshairVisible(true);

        plot.setRenderer(new /*OptimisedXYLineAndShapeRenderer()*/ StandardXYItemRendererFast());
        XYItemRenderer renderer = plot.getRenderer();
        renderer.setBaseToolTipGenerator(new MyXYSeriesToolTipGenerator());
        renderer.setBaseItemLabelGenerator(new MyXYSeriesItemLabelGenerator());
        renderer.setLegendItemLabelGenerator(new MyXYSeriesLegendItemLabelGenerator());
        if (renderer instanceof XYLineAndShapeRenderer) {
            XYLineAndShapeRenderer r = (XYLineAndShapeRenderer) renderer;
            r.setBaseShapesVisible(false);
            r.setBaseShapesFilled(true);
        }

        SimpleDateFormat dateFormat = getDateFormatAbscissa();
        if (dateFormat != null){
            DateAxis axis = (DateAxis) plot.getDomainAxis();
            axis.setDateFormatOverride(dateFormat);
        }   

        return vChart;
    }

My problem is that when too many variables are added to the chart (a TimeSeriesChart) the caption takes too much space and the graph disappears from the view:

ChartComposite with 2 series

ChartComposite many series

I tried to create a ScrollComposite to scroll in the ChartComposite and the result is a little better; but it only makes it possible to add more items in the caption before the graph disappears again:

ScrolledComposite scrollableChart = new ScrolledComposite(parent, SWT.BORDER|SWT.V_SCROLL);

chartComposite = new MyChartComposite(this, scrollableChart, SWT.NONE, chart, true);
//chartComposite = new MyChartComposite(this, parent, SWT.NONE, chart, true);
//chartComposite.setLayoutData(new GridData(GridData.FILL_BOTH));

scrollableChart.setContent(chartComposite);
scrollableChart.setExpandVertical(true);
scrollableChart.setExpandHorizontal(true);
scrollableChart.setMinSize(ChartComposite.DEFAULT_MINIMUM_DRAW_WIDTH, ChartComposite.DEFAULT_MINIMUM_DRAW_WIDTH);

My question is: How to provide a real scrollbar to the ChartComposite in order to keep the graph when many series are plotted on the graph?

score 2 · Accepted Answer · edited May 23 '17 at 11:50

2

I was able to sync a slider to the XYSeries in SWT using a ChartComosite and Slider objects through the use of FormData. And every time I move the slider I capture that event and update the chart myself according to my needs.

My use case may be different than yours, but it's worth to take a look to my answer here.

If you have questions regarding my implementation, described in that answer, feel free to ask for details

edited May 23 '17 at 11:50

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answered Jan 12 '12 at 14:19

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Thanks I just found your post a few hours ago, I will try to adapt your solution to my needs. – zeropouet Jan 12 '12 at 14:56

score 1 · Answer 2 · answered Jan 24 '12 at 15:32

After several unsuccessful tries, I decided to limit the number of LegendItem shown on the chart.

To change the legend items to display in the LegendTitle I used a slider. The most difficult part was to recreate the a new LegendTitle when using the slider; I am not sure that my solution is optimal or elegant but at least it is working.

Result

To make this possible I needed to listen to series creation (ChartChangeEventType.DATASET_UPDATED) to refresh the LegendTitle and set slider values.

So here is the code:

public class MyExampleChartComposite extends ChartComposite {
    // snip
    /**
     * A slider to choose the legend items to display
     */
     private Slider legendSlider;
     /**
     * Number of legend items to display on the chart
     */
     private final static int NUMBER_OF_LEGENDITEMS_TO_DISPLAY = 10;

     private void createPartControl(Composite parent, int style) {
         JFreeChart chart = createChart();
         setChart(chart);
         legendSlider = new Slider(parent, SWT.NONE|SWT.H_SCROLL);
         legendSlider.addSelectionListener(new SelectionListener() {
             @Override
             public void widgetSelected(SelectionEvent arg0) {
                      refreshLegend();
             }
         });

     private JFreeChart createChart() {
         chart.addChangeListener(new ChartChangeListener() {    
             @Override
             public void chartChanged(ChartChangeEvent e) {
                  if (e.getType().equals(ChartChangeEventType.DATASET_UPDATED)) {
                      refreshLegend();
                  }
             }
         });
    }

    /**
     * Refresh the the LegendItems and the slider,
     * according to slider selection.
     */
    public void refreshLegend() {
        // Display LegendItems according to the selection
        // display the 10 nearest legend item (current selected element included)
        int begin = legendSlider.getSelection() - (NUMBER_OF_LEGENDITEMS_TO_DISPLAY/2);
        int end = legendSlider.getSelection() + (NUMBER_OF_LEGENDITEMS_TO_DISPLAY/2 -1);
        int seriesEndIndex = Math.max(getSeriesCount()-1, 0);
        // if begin is less than 0
        // set it to 0, and increase end to display 10 items
        if (begin < 0) {
            begin = 0; 
            end = NUMBER_OF_LEGENDITEMS_TO_DISPLAY - 1;
        }
        // if end is greater than the number of series plotted
        // set it to the max possible value and increase begin to
        // display 10 items
        if  (end > seriesEndIndex) {
            end = seriesEndIndex;  
            begin = seriesEndIndex - (NUMBER_OF_LEGENDITEMS_TO_DISPLAY - 1);
        }
        end = Math.min(seriesEndIndex, end);
        begin = Math.max(begin, 0);
        // Refresh only if begin != end
        if (end != begin) {
            refreshLegendItems(begin, end);
            refreshLegendSlider();
        } else {
            // in this case no more series are plotted on the chart
            // clear legend
            getChart().clearSubtitles();
        }
    }
    /**
     * Refresh the LegendTitle.
     * Display only LegendItems between beginIndex and toIndex,
     * to preserve space for the chart.
     * @param beginIndex index of the {@link LegendItemCollection} used as the beginning of the new {@link LegendTitle}
     * @param endIndex index of the {@link LegendItemCollection} used as the end of the new {@link LegendTitle}
     */
    private void refreshLegendItems(int beginIndex, int endIndex) {
        // Last 10 items
        final LegendItemCollection result = new LegendItemCollection();
        // get the renderer to retrieve legend items
        XYPlot plot = getChart().getXYPlot();
        XYItemRenderer renderer = plot.getRenderer();
        // Number of series displayed on the chart 
        // Construct the legend
        for (int i = beginIndex; i <= endIndex; i++) {
            LegendItem item = renderer.getLegendItem(0, i);
            result.add(item);
        }
        // Because the only way to create a new LegendTitle is to
        // create a LegendItemSource first
        LegendItemSource source = new LegendItemSource() {
            LegendItemCollection lic = new LegendItemCollection();
            {lic.addAll(result);}
            public LegendItemCollection getLegendItems() {  
                return lic;
            }
        };
        // clear previous legend title
        getChart().clearSubtitles();
        // Create the new LegendTitle and set its position
        LegendTitle legend = new LegendTitle(source);
        legend.setHorizontalAlignment(HorizontalAlignment.CENTER);
        legend.setVerticalAlignment(VerticalAlignment.CENTER);
        legend.setPosition(RectangleEdge.BOTTOM);
        legend.setBorder(1.0, 1.0, 1.0, 1.0);
        legend.setVisible(true);
        // Add the LegendTitle to the graph
        getChart().addLegend(legend);
    }

    /**
     * Set values of the slider according to the number of series
     * plotted on the graph
     */
    private void refreshLegendSlider() {
        int max = getSeriesCount() -1;
        int selection = Math.min(legendSlider.getSelection(), max);
        legendSlider.setValues(selection, 0, max, 1, 1, 1);
    }
}

My issue was quite different from yours but I was able to use the insight you shared regarding these JFree classes (especially `LegendTitle` and `LegendItemSource`). Thanks much! — Jesse Hautala, Sep 04 '12 at 14:45

JfreeChart limit the number of legend items displayed

2 Answers2