MPAndroidChart: Have one graph mirror the zoom/swipes on a sister graph

Question

I have two line graphs that show complementary data over the same time period. Is there any way to send any touch events received by one graph to the other? I essentially want it so that the graphs always show the same viewing rectangle (at least on horizontally). So if a user swipes left 'n' units on the top graph, the bottom graph will automatically scroll left 'n' units to match.

Answer 1

Zooms can be done with the current MPAndroidChart release, for scrolling check out or wait for my extension to be merged: https://github.com/PhilJay/MPAndroidChart/pull/545

You need to set up an OnChartGestureListener on the master chart that copies the translation matrix values to the slave charts:

public class CoupleChartGestureListener implements OnChartGestureListener {

    private Chart srcChart;
    private Chart[] dstCharts;

    public CoupleChartGestureListener(Chart srcChart, Chart[] dstCharts) {
        this.srcChart = srcChart;
        this.dstCharts = dstCharts;
    }

    [...other overrides...]

    @Override
    public void onChartScale(MotionEvent me, float scaleX, float scaleY) {
        //Log.d(TAG, "onChartScale " + scaleX + "/" + scaleY + " X=" + me.getX() + "Y=" + me.getY());
        syncCharts();
    }

    @Override
    public void onChartTranslate(MotionEvent me, float dX, float dY) {
        //Log.d(TAG, "onChartTranslate " + dX + "/" + dY + " X=" + me.getX() + "Y=" + me.getY());
        syncCharts();
    }

    public void syncCharts() {
        Matrix srcMatrix;
        float[] srcVals = new float[9];
        Matrix dstMatrix;
        float[] dstVals = new float[9];

        // get src chart translation matrix:
        srcMatrix = srcChart.getViewPortHandler().getMatrixTouch();
        srcMatrix.getValues(srcVals);

        // apply X axis scaling and position to dst charts:
        for (Chart dstChart : dstCharts) {
            if (dstChart.getVisibility() == View.VISIBLE) {
                dstMatrix = dstChart.getViewPortHandler().getMatrixTouch();
                dstMatrix.getValues(dstVals);
                dstVals[Matrix.MSCALE_X] = srcVals[Matrix.MSCALE_X];
                dstVals[Matrix.MTRANS_X] = srcVals[Matrix.MTRANS_X];
                dstMatrix.setValues(dstVals);
                dstChart.getViewPortHandler().refresh(dstMatrix, dstChart, true);
            }
        }
    }

}

Then set up your master/slave connections for example like this:

//
// Couple chart viewports:
//

tripChart.setOnChartGestureListener(new CoupleChartGestureListener(
        tripChart, new Chart[] { powerChart, energyChart }));
powerChart.setOnChartGestureListener(new CoupleChartGestureListener(
        powerChart, new Chart[] { tripChart, energyChart }));
energyChart.setOnChartGestureListener(new CoupleChartGestureListener(
        energyChart, new Chart[] { tripChart, powerChart }));

Answer 2

You need add this to CoupleChartGestureListener

    @Override
public void onChartGestureStart(MotionEvent me, ChartTouchListener.ChartGesture lastPerformedGesture) {
    ((BarLineChartTouchListener) srcChart.getOnTouchListener()).stopDeceleration();
    for (Chart dstChart : dstCharts) {
        if (dstChart.getVisibility() == View.VISIBLE) {
            ((BarLineChartTouchListener) dstChart.getOnTouchListener()).stopDeceleration();
        }
    }
}