Fix data selection following zooming with mouse

[mosherubin]

The Problem

Data selection works fine when the chart is unzoomed, with an app's selectionChanged() callback being invoked following data point selection. When the chart is zoomed, however, the selectionChanged() callback is not invoked.

Playing with zooming shows that data selection always fails following zooming using the mouse (i.e., mouse button down + drag). When zooming using the mouse wheel, data selection works for the first few zoom-in mouse wheel works. Once the chart has been enlarged a few times, selection fails.

Reproducing the Problem

The problem can be reproduced easily with a minimally modified SelectionDemo1.java file.

The Technical Explanation

Examining the FSE code shows that the reason for SelectionChanged() not being called following zooming is because the hash value of the DatasetSelectionExtension<XYCursor> object registered in function createDemoPanel() is modified because of zooming. This causes the statement "registeredExtensions.get(dataset)" in DatasetExtensionManager.getExtension() to return null:

public <T extends DatasetExtension> T getExtension(Dataset dataset, 
            Class<T> interfaceClass) {        
        if (interfaceClass.isAssignableFrom(dataset.getClass())) {
            //the dataset supports the interface
            return interfaceClass.cast(dataset);
        } else {
           List<DatasetExtension> extensionList 
                    = registeredExtensions.get(dataset);
            if (extensionList != null) {
                for (DatasetExtension extension : extensionList) {
                    if (interfaceClass.isAssignableFrom(extension.getClass())) {
                        //the dataset does not support the extension but
                        //a matching helper object is registered for the dataset
                        return interfaceClass.cast(extension);
                    }
                }
            }
        }
                
        return null;        
    }

Drilling down further shows that the Calendar member variable workingCalendar has some of its member variables changed due to zooming.

The hash returned by the Calendar class takes these into account, causing the HashMap get() to fail and return null, preventing selectionChanged() from being invoked.

For an explanation complete with screen captures, see the following PDF file.

The Proposed Fix

I believe workCalendar is unsafe to include in the hash of a TimesSeriesCollection object and should be removed. I would like to propose removing it from TimeSeriesCollection.hashCode(). When I made the fix locally and rebuilt FSE, data selection works perfectly on both zoomed and non-zoomed charts.