How to draw a navigation path using Canvas onDraw() in android java

Question

I am new to java drawing and I would like to implement a navigation system so a user can navigate on a map. The java function 'onDraw' is implement so it shows the location of the user on the map and also show his movements. Below are my codes:

class CanvasView extends View {
        private Paint paint = new Paint();
        private Path path = new Path();
        private float lineX = Position.x_axis;
        private float lineY = Position.y_axis;
        private float lastX = Position.x_axis;
        private float lastY = Position.y_axis;

        public CanvasView(Context context) {
            super(context);
            paint.setAntiAlias(true);
            paint.setStrokeWidth(10f);
            paint.setColor(Color.BLACK);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);

        }

        @Override
        protected void onDraw(Canvas canvas) {
            // TODO Auto-generated method stub
            super.onDraw(canvas);
            drawRotateImage(canvas);
            canvas.drawPoint(Position.x_axis, Position.y_axis, paint);

            Path path = new Path();
            path.moveTo(lastX, lastY);
            path.lineTo(lineX,lineY);
            canvas.drawPath(path, paint);
        }

        private void stepDetector (float step) {
            stepCount += (int) step;
            distance = stepCount * 30;
            lineX = (float) (lineX + 30);
            lineY = (float) (lineY + 30);
            invalidate();
            lastX = lineX;
            lastY = lineY;
        }
}

The stepdetector is called each time a step has been detected and it should repaint the canvas to show to movements. Noting that the previous movement line needs to be visible, that is it should be a continuous line.

I am having issues to get the navigation line path. It would be grateful if I can get some help on it.

Thank you in advance.

Answer 1

The onDraw draws a fresh copy of the contents everytime and does not remain old information. For what you are trying to draw, you can keep a list of type Position and add the new position to the list when stepDetector is called.

Then, inside onDraw , iterate over the list and draw lines connecting all the points from the list.

Answer 2

try this, make list and for every step add points, and in ondraw draw all points from list

class CanvasView extends View {
        List<Point> points;
        private Paint paint = new Paint();
        private Path path = new Path();
        private float lineX = Position.x_axis;
        private float lineY = Position.y_axis;
        private float lastX = Position.x_axis;
        private float lastY = Position.y_axis;

        public CanvasView(Context context) {
            super(context);
            paint.setAntiAlias(true);
            paint.setStrokeWidth(10f);
            paint.setColor(Color.BLACK);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);
            points=new ArrayList<>();

        }

        @Override
        protected void onDraw(Canvas canvas) {
            // TODO Auto-generated method stub
            super.onDraw(canvas);
            drawRotateImage(canvas);
            canvas.drawPoint(Position.x_axis, Position.y_axis, paint);
            // now here draw all points from list
            Path path = new Path();
            path.moveTo(lastX, lastY);
            path.lineTo(lineX,lineY);
            canvas.drawPath(path, paint);
        }

        private void stepDetector (float step) {
            stepCount += (int) step;
            distance = stepCount * 30;
            lineX = (float) (lineX + 30);
            lineY = (float) (lineY + 30);
            invalidate();
            lastX = lineX;
            lastY = lineY;
            // add every point to the list after step
        }

class Point{
float x,y;     

}

 }