Have you added LineDataSet?
LineData xData = mChart.getData();
ILineDataSet x = xData.getDataSetByIndex(0);
x = createXSet();
xData.addDataSet(x);
xData.addEntry(new Entry(5f, 21, 0);
xData.notifyDataChanged();
mChart.notifyDataSetChanged();
mChart.setVisibleXRangeMaximum(30);
mChart.moveViewToX(xData.getEntryCount());
private LineDataSet createXSet(boolean drawPoints) {
LineDataSet set = new LineDataSet(null, "x");
set.setColor(Color.GREEN);
set.setLineWidth(2f);
set.setCircleRadius(2f);
set.setCircleColor(Color.WHITE);
set.setFillAlpha(65);
set.setFillColor(Color.GREEN);
set.setHighLightColor(Color.rgb(244, 117, 117));
set.setValueTextColor(Color.WHITE);
set.setValueTextSize(9f);
set.setDrawValues(false);
return set;
}