Hi, I am developing android app in android studio in JAVA. And I am using DataChartView to display a chart the problem is I am unable to see anything plotted. There is just one grey line. Following is my code using the sample data from the documentation

public class CategoryDataSample extends CategoryDataCollection {


 public CategoryDataSample() {
        this.add(new CategoryDataPoint("A", 85, 80, 95));
 ...
 this.add(new CategoryDataPoint("B", 50, 45, 65));
 this.add(new CategoryDataPoint("Z", 100, 75, 95));
 int i = 0;
 for (CategoryDataPoint dataPoint : this) {
            dataPoint.setIndex(i++);
        }
    }

public class CategoryDataPoint  {

    private int _index;
 private String _category;
 private double _value;
 private double _high;
 private double _low;

 public CategoryDataPoint(String category, double value, double high, double low) {
        _category = category;
 _value = value;
 _high = high;
 _low = low;
 }

    public CategoryDataPoint(String category, double value) {
        _category = category;
 _value = value;
 }

    public int getIndex() {
        return _index;
 }

    public int setIndex(int value) {
        _index = value;
 return _index;
 }

    public String getCategory() {
        return _category;
 }

    public String setCategory(String category) {
        _category = category;
 return category;
 }

    public double getValue() {
        return _value;
 }

    public double setValue(double value) {
        _value = value;
 return _value;
 }

    public double getHigh() {
        return _high;
 }

    public double setHigh(double value) {
        _high = value;
 return _high;
 }

    public double getLow() {
        return _low;
 }

    public double setLow(double value) {
        _low = value;
 return _low;
 }
}

and the 3rd class is following

class CategoryDataCollection extends ArrayList<CategoryDataPoint> {

}

And below is my usage in Fragment

CategoryDataSample data =
        new CategoryDataSample();

DataChartView chart = new DataChartView(chartContainer.getContext());
chart.setHorizontalZoomable(true);
chart.setVerticalZoomable(false);

NumericYAxis yAxis = new NumericYAxis();
yAxis.setLabel("y");
yAxis.setLabelTextSize(10.0f);

CategoryXAxis xAxis = new CategoryXAxis();
xAxis.setDataSource(data);
xAxis.setLabel("x");
xAxis.setLabelTextSize(10.0f);

chart.addAxis(xAxis);
chart.addAxis(yAxis);

LineSeries series = new LineSeries();
series.setDataSource(data);
series.setValueMemberPath("");
series.setTitle("Coal");
series.setXAxis(xAxis);
series.setYAxis(yAxis);

chart.addSeries(series);

chartContainer.addView(chart);

chartContainer is a FrameLayout in my XML

the only output I get is a grey line which is so wierd as i am following the exact same code provided in the documentation. Please help.