android - 在 aChartEngine 中对 XYSeries 使用 remove(int index) 函数

Question

我正在编写一段代码，其中必须通过重复调用 aSyncTask 来不断更新图形。但为确保图表不会过于压缩，我计划移除/删除最旧的条目超过某个点。目前我的代码如下:

int counter = 0;
private class UpdateLineGraphAsync extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... params) {
        // add the next series value
        series.add(counter, Math.sin((double) counter / 100));
        counter += 20;
        if (counter > 500)
            series.remove(0);
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        ((GraphicalView) lineGraph).repaint(); // repaints the graph!
    }

}

但是当我调用 remove(0) 时，这段代码一直给我一个空点异常；谁能解释 XYSeries.remove(index) 函数是如何工作的？我在某处读到它是一个后进先出结构。这是真的？如何纠正这个错误？即使调用一次删除函数也会出错。

错误代码是:

07-03 17:27:36.080: E/AndroidRuntime(1229): FATAL EXCEPTION: AsyncTask #2
07-03 17:27:36.080: E/AndroidRuntime(1229): java.lang.RuntimeException: An error occured while executing doInBackground()
07-03 17:27:36.080: E/AndroidRuntime(1229):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at java.util.concurrent.FutureTask.run(FutureTask.java:138)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at java.lang.Thread.run(Thread.java:1027)
07-03 17:27:36.080: E/AndroidRuntime(1229): Caused by: java.lang.NullPointerException
07-03 17:27:36.080: E/AndroidRuntime(1229):     at org.achartengine.model.XYSeries.getY(XYSeries.java:169)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at org.achartengine.model.XYSeries.initRange(XYSeries.java:83)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at org.achartengine.model.XYSeries.remove(XYSeries.java:140)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at com.clearbridgevitalsigns.cardioleaf.LiveView$UpdateLineGraphAsync.doInBackground(LiveView.java:121)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at com.clearbridgevitalsigns.cardioleaf.LiveView$UpdateLineGraphAsync.doInBackground(LiveView.java:1)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
07-03 17:27:36.080: E/AndroidRuntime(1229):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
07-03 17:27:36.080: E/AndroidRuntime(1229):     ... 4 more

Answer 1

我也遇到过同样的问题。我不知道为什么，但我想这是由于并发访问来自 achartengine 的系列数据。我设法使用另一种方法来避免这个问题，即使用 renderer.setXAxisMin 和 renderer.setXAxisMax 移动显示，而无需自己处理系列。