Dynamic XY plot

[Ted Hill]

Hello,

I want to make a fairly simple XY plot having about 25 x,y pairs.

Then I want to be able to periodically change some of the y values and have the chart redraw itself.

I am new to JFreeChart, please suggest for me:

1. Which dataset class to use
2. How to update a y component of an existing x,y pair.
3. How to tell the chart to redraw after updating the dataset.

Thank you very much,

Ted Hill

[josh]

private XYSeries series1=new XYSeries("");
private XYSeriesCollection dataset = new XYSeriesCollection();

//update your y Value by doing this
//note, x is not the x value, it is the xth point (1st, 2nd, 22nd point, etc)
series1.update(x,Number);//Number is a Double or something

//to get your graph to redraw
dataset=new XYSeriesCollection;
dataset.addSeries(series1);
chart.setDataset(dataset);

[David Gilbert]

Josh has set you off in the right direction, except I'll add a couple of comments:

1) In recent versions of JFreeChart, the dataset is managed by the plot, so instead of:

chart.setDataset(dataset);

you should use:

XYPlot plot = chart.getXYPlot();
plot.setDataset(dataset);

2) Once you have set the dataset, any changes you make to it should automatically be reflected in the chart (it redraws itself any time the data changes).

Regards,

DG.

[Ted Hill]

Thanks,

I followed your advice on choice of Dataset.
However instead of calling setDataset(modifiedDataset), I have subclassed XYSeriesCollection to expose fireDatasetChanged() as follows

class DynamicXYSeriesCollection extends XYSeriesCollection
{
public void fireDatasetChanged()
{
super.fireDatasetChanged();
}
}

So after I do
series1.update(x,Number);

I call myDataset.fireDatasetChanged(); and the chart redraws.

Do you see any problem with doing it this way?

Thank you,

Ted Hill

[David Gilbert]

You shouldn't need to do this. When you call the update method in XYSeries, it will do a fireSeriesChanged() call. This should trigger a notification to XYSeriesCollection (via the seriesChanged(...) method in AbstractSeriesDataset) which should then call fireDatasetChanged() for you. If that is not happening, it is a bug...

Regards,

DG.

[Ted Hill]

David,

Thanks for the tip.

You are right, it updates without the overt call to fireDatasetChanged()


Great piece of work!

Ted Hill