How can I clear all data in a JavaFX graph? - graph

Question

I get this weird exception and I think that it is a bug. I am trying to clear a Series, which contains a list of points to plot in the graph. However, after clearing I want to add new Data and this gives me a nul pointer exception. My code:
public static void main(String[] args) {
Series<String, Number> series = new Series<String, Number>();
Number value1 = new Integer(5);
Number value2 = new Integer(6);
Data<String, Number> point1 = new Data<String, Number>("Something", value1);
Data<String, Number> point2 = new Data<String, Number>("Something", value2);
series.getData().add(point1);
series.getData().add(point2);
series.getData().clear();
Number value3 = new Integer(7);
Data<String, Number> point3 = new Data<String, Number>("Something", value3);
**series.getData().add(point3);**
}
I get a null pointer exception at the marked code line. I just need a way to reset this series, but to me it seems like a bug in JavaFX. I use Java 8, which has JavaFX as an integration.
Can someone help me?

Answer 1

The technical reason is a NPE in the listener on the data list, installed by series:
if (c.getAddedSize() > 0) {
for (Data<X,Y> itemPtr = begin; itemPtr != null; itemPtr = itemPtr.next) {
if (itemPtr.setToRemove) {
getChart().dataBeingRemovedIsAdded(itemPtr, Series.this);
itemPtr.setToRemove = false;
}
}
}
This will throw on the next addition if an item had been deleted while the chart is null.
The deeper reason is the slightly convoluted delete mechanism: the series doesn't delete the item itself but only marks it as ready for deletion. Then it delegates the change to its chart which then calls back into the series to do the actual delete. And that mechanism breaks if there is no chart.
Real solutions might be hard from the outside, because everything is so tightly and secretly knitted - no way to hook your own listener to do the actual remove. If you really have to manipulate (remove items) the series without a chart attached, you might try to implement a dummy chart and set that to the series.