toScreenPoints achartengine上的空点异常

Question

我试图访问屏幕坐标相对于我用来绘制图形的值。但是现在我试图在XYChart类中使用toSreeenPoint方法来协调访问。 这是我正在使用的代码，

  if (layout != null) {
        layout.removeAllViews();
        mChartView = ChartFactory.getCubeLineChartView(MyActivity.this, dataset, multiRenderer, 0.33f);

        layout.addView(mChartView);

       // mChartView = null;
        mChartView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View view, MotionEvent event) {
                SeriesSelection ss = mChartView.getCurrentSeriesAndPoint();
                XYChart chart = new LineChart(dataset, multiRenderer);
                XYSeries series = dataset.getSeriesAt(0);
                if(chart != null) {
                    for(int i = 0; i < series.getItemCount(); i++) {
                        Log.d(TAG, "Serieous COunt"+series.getX(i));
                        Log.d(TAG, "Serieous COunt#1"+series.getY(i));

                        Log.d(TAG, "Type is"+chart.getChartType());

                      double[] xy = chart.toScreenPoint(new double[]{series.getX(i), series.getY(i)});
                        //Log.d(TAG, "Check is right" + chart.getSeriesAndPointForScreenCoordinate(new Point((float) xy[0], (float) xy[1])));
                    }
                } else {
                    Log.d(TAG, "Check is Wrong");
                }


                return false;
            }
        });
    }

但是有些原因它在chart.toScreenPoint行上崩溃了NULL POint Exception。我检查使用longs没有什么是null直到该行。请帮助找到我做错的事情......