JfreeChart limit the number of legend items displayed - scroll

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?

Answer 1

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

Answer 2

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.
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);
}
}