Android - How to keep default zoom/pan features with custom x-axis labels using AChartEngine

Question

How do I apply custom x-axis labels to my AChartEngine BarGraph while keeping the same zoom/pan functionality as when default labels are used? The problem is that I have 100+ data points so I only want to draw 5 or 6 labels on the screen at a time.

The default functionality originally draws 3 labels (0, 50, and 100 in my case) and when zooming in, 4/5 labels are drawn. When panning left or right, the labels move along with the corresponding bars:

enter image description here

I have attempted two approaches however neither of them give me the same zoom and pan functionality as the default labels.

1) Generate 5 evenly spaced labels when the graph is first created.

The problem with this is that it only creates 5 labels so when you zoom in too far, no labels are shown.

//For 100 data points, add five labels every 20 datapoints
mRenderer.addXTextLabel(0, "label 1");
mRenderer.addXTextLabel(20, "label 2");
mRenderer.addXTextLabel(40, "label 3");
mRenderer.addXTextLabel(60, "label 4");
mRenderer.addXTextLabel(80, "label 5");
mRenderer.setXLabels(0);

2) Implement the ZoomListener and PanListener interfaces on my GraphicalView.

This solution almost works, however the labels are always in fixed locations and are just "updated" with a new value when the graph is panned left or right. I need them to move with their corresponding bars.

graphicalView.addZoomListener( new ZoomListener() {
    @Override
    public void zoomApplied(ZoomEvent e) {
        double start = mRenderer.getXAxisMin();
        double stop = (double)mRenderer.getXAxisMax();
        double step = (double)(stop - start) / 5;
        mRenderer.clearXTextLabels();
        for (double i = start; i <= stop; i += step) 
            mRenderer.addXTextLabel(i+1, "label"+(int)i);
        mRenderer.setXLabels(0);
      }

    @Override
    public void zoomReset() { }
}, true, true);

graphicalView.addPanListener(new PanListener() {
    @Override
    public void panApplied() {
        double start = mRenderer.getXAxisMin();
        double stop = (double)mRenderer.getXAxisMax();
        double step = (double)(stop - start) / 5;
        mRenderer.clearXTextLabels();
        for (double i = start; i <= stop; i += step) 
            mRenderer.addXTextLabel(i+1, "label"+(int)i);
        mRenderer.setXLabels(0);                
    }
});

The custom labels that I want to implement are time in minutes. Can this be done using the TimeSeries class with a bar chart?

Dan D. Dan D. · Accepted Answer · 2013-05-06T17:40:52

Your solution is quite good, so I can only suggest an improvement for getting to the labels behavior you need: Use MathHelper.getLabels(start, stop, approxNumLabels) instead of your for loop between start and stop.

So your for loop would become something like this:

List<Double> labels = MathHelper.getLabels(start, stop, 10);
for (Double label : labels) {
  mRenderer.addXTextLabel(label, "label " + label);
}

Android - How to keep default zoom/pan features with custom x-axis labels using AChartEngine

1 Answers