Drawing touch-interactive charts in Android

Question

I need to use charts in Android and have unsuccessfully tried the various aChartEngine , AndroidPlot , and other libraries. I need the user to tap on an item and trap the event, those libraries do not handle this.

So I decided to build charts from scratch. I think to use canvas but I would like to know how can I get the touch event on a drawn item (if possible avoiding to get the touch coordinates and seeing if they intersect with an object, if I handle device rotation this can be difficult to handle).

Has anyone examples of canvas drawn images that can be touched?

Answer 1

It is easy. On a view you are using to draw you chart add a TouchListener and then check if the touched point is within your circle. In this example I'm checking if touched point is within rectangle around the pie chart:

this.setOnTouchListener(new View.OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                float x = event.getX();
                float y = event.getY();
                if (x < (centreX-r) || x> (centreX+r) || y <(centreY-r) || y>(centreY+r)) {
                    return false;
                }
                //do whatever you need to do
                return true;
            }
        });

Of course, if you need to know exactly which slice was pressed, you will have to add some logic to determine the slice based on the point and angle.