MPAndroidChart - removing old data points in real time chart

Question

I'm using MPAndroidChart to create some real time plots of accelerometer data. It seems that memory usage continuously grows the longer you leave the app running so I tried to find a way to remove old data points once they are out of view of the charts scrolling window.

The problem is that once I hit the limit I set for the max number of points to keep/display, points are no longer added but the chart keeps scrolling. The size of my data remains constant (as it should as I'm both adding a new point and removing an old one every update), but no new data gets displayed in the chart anymore.

In my fragment, I'm creating the chart like this in onCreateView:

accChart = (LineChart) view.findViewById(R.id.accChart);
        accChart.setOnChartValueSelectedListener(this);

        LineData data = new LineData();
        data.setValueTextColor(Color.WHITE);

        accChart.setData(data);

Then I listen for accelerometer events using sensor manager, and add an entry every 100ms in onSensorChanged:

public void onSensorChanged(SensorEvent event) {
        sensor = event.sensor;

        curAccX = event.values[0];
        curAccY = event.values[1];
        curAccZ = event.values[2];

        long curTime = System.currentTimeMillis();
        long diffTime = (curTime - lastUpdate);

        // only allow one update every POLL_FREQUENCY.
        if(diffTime > POLL_FREQUENCY) {
            lastUpdate = curTime;

            addEntry(curAccX, curAccY, curAccZ);
        }

    }

Then to add the entries in addEntry I'm doing this:

private void addEntry(float curAccX, float curAccY, float curAccZ){
        LineData data = accChart.getData();

        if (data != null) {

            ILineDataSet xData = data.getDataSetByIndex(0);
            ILineDataSet yData = data.getDataSetByIndex(1);
            ILineDataSet zData = data.getDataSetByIndex(2);

            if (xData == null) {
                xData = createSetX();
                data.addDataSet(xData);
            }
            if (yData == null) {
                yData = createSetY();
                data.addDataSet(yData);
            }
            if (zData == null) {
                zData = createSetZ();
                data.addDataSet(zData);
            }

            // add a new x-value first
            data.addXValue(String.valueOf(System.currentTimeMillis()));

            data.addEntry(new Entry(curAccX, xData.getEntryCount()), 0);
            data.addEntry(new Entry(curAccY, yData.getEntryCount()), 1);
            data.addEntry(new Entry(curAccZ, zData.getEntryCount()), 2);

            //This is where I remove the first entry for each series
            if (xData.getEntryCount() > MAX_POINTS_DISPLAYED){
                xData.removeFirst();
                yData.removeFirst();
                zData.removeFirst();
            }

            // let the chart know it's data has changed
            accChart.notifyDataSetChanged();

            // limit the number of visible entries
            accChart.setVisibleXRangeMaximum(MAX_POINTS_DISPLAYED);

            // move to the latest entry
            accChart.moveViewToX(data.getXValCount());
        }
    }

I think the problem lies in my usage of removeFirst. If I uncomment all those lines, data keeps getting plotted. If I uncomment removeFirst for only one of the series, that one gets plotted fine, but the other 2 are empty as I described above

Answer 1

Try calling data.notifyDataChanged() directly after adding the entries.