How to enable cubic lines in MPAndroidChart library?

Try using something like this

lineDataSet.setDrawCubic(true);

It worked for me, here lineDataSet is your LineDataSet instance.

Update for v3.0.0 and onwards:

lineDataSet.setMode(LineDataSet.Mode.CUBIC_BEZIER);

Try to add set mode of LineData set, enable draw filled and set the fill color

    lineDataSet.setMode(LineDataSet.Mode.CUBIC_BEZIER)
    lineDataSet.setDrawFilled(true)
    lineDataSet.setFillColor(ContextCompat.getColor(context,R.color.green))