如何使用onTouchEvent或任何其他方法在graphView上绘制形状？

public class GraphView extends View {
    private Paint paint;
    private Path path;
    private float startX, startY, endX, endY;

    public GraphView(Context context) {
        super(context);
        init();
    }

    public GraphView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        paint = new Paint();
        paint.setColor(Color.BLACK);
        paint.setStrokeWidth(5f);
        paint.setStyle(Paint.Style.STROKE);
        path = new Path();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPath(path, paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                startX = event.getX();
                startY = event.getY();
                path.moveTo(startX, startY);
                return true;
            case MotionEvent.ACTION_MOVE:
                endX = event.getX();
                endY = event.getY();
                path.lineTo(endX, endY);
                break;
            case MotionEvent.ACTION_UP:
                endX = event.getX();
                endY = event.getY();
                path.lineTo(endX, endY);
                break;
            default:
                return false;
        }
        invalidate();
        return true;
    }
}