aChart Engine和NullPointerException

Question

我正在尝试在我的项目中使用aChart Engine，但我总是遇到这个令人讨厌的异常：

06-09 21:47:59.045: E/AndroidRuntime(19635): FATAL EXCEPTION: main
06-09 21:47:59.045: E/AndroidRuntime(19635): java.lang.NullPointerException
06-09 21:47:59.045: E/AndroidRuntime(19635):    at android.view.GLES20Canvas.drawBitmap(GLES20Canvas.java:739)
06-09 21:47:59.045: E/AndroidRuntime(19635):    at android.view.GLES20RecordingCanvas.drawBitmap(GLES20RecordingCanvas.java:91)
06-09 21:47:59.045: E/AndroidRuntime(19635):    at org.achartengine.GraphicalView.onDraw(GraphicalView.java:176)

有人能帮助我吗？