MPAndroidChart: negative values in pie chart or custom labels

问题

In my Android application I have to show my income and expense amounts in a piechart. The expense amounts will be negative. The amounts are of type float. So is it possible to display both negative and positive values in a pie chart using MPAndroidChart library?

I have tried with some negative and positive integer values and the result is horible. The pie-chart will behave crazy like a rummy board or illumination screen.

If I can't have negative values in a pie chart, is it possible to show the labels in negative by even though the actual values are positive?

回答1:

You are essentially asking how to customise the labels on an MPAndroidChart chart. This can be done easily by writing your own implementation of the interface IValueFormatter.

IValueFormatter has one method that you need to implement:

getFormattedValue(float value, Entry entry, int dataSetIndex, ViewPortHandler viewPortHandler)`

You use the parameters of the method to construct the label you want as a String. You want a minus sign "-" in front so you simply do this:

return "-" + mFormat.format(value) + " %";

Here is the complete implementation:

public class NegativePercentFormatter implements IValueFormatter

    protected DecimalFormat mFormat;

    public NegativePercentFormatter() {
        mFormat = new DecimalFormat("###,###,##0.0");
    }


    public NegativePercentFormatter(DecimalFormat format) {
        this.mFormat = format;
    }

    @Override
    public String getFormattedValue(float value, Entry entry, int dataSetIndex, ViewPortHandler viewPortHandler) {
        return "-" + mFormat.format(value) + " %";
    }
}

来源：https://stackoverflow.com/questions/41075105/mpandroidchart-negative-values-in-pie-chart-or-custom-labels