I am using an Aynctask to make an API call to build a chart of bitcoin values using blockchain.info API and the Android achartengine Library.
Through deugging I see that the API call is successful and the JSON data gets pulled, but for some reason it crashes and LogCat gives me the error "An error occurred while executing doInBackground. I know that you cannot access UI elements in doInBackground, but I was not trying to do that, so does anyone know what might be wrong here?
public class GraphActivity extends Activity {
private GraphicalView m_chart;
private XYMultipleSeriesDataset m_dataset = new XYMultipleSeriesDataset();
private XYMultipleSeriesRenderer m_renderer = new XYMultipleSeriesRenderer();
private XYSeries m_currentSeries;
private XYSeriesRenderer m_currentRenderer;
private void initChart()
{
m_currentSeries = new XYSeries("Bitcoin Price");
m_dataset.addSeries(m_currentSeries);
m_currentRenderer = new XYSeriesRenderer();
m_renderer.addSeriesRenderer(m_currentRenderer);
}
private void addBtcPriceData(xyCoords[] coords)
{
int length = coords.length;
for(int i = 0; i < length; ++i)
{
m_currentSeries.add(coords[i].x, coords[i].y);
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_graph);
}
@Override
protected void onResume()
{
super.onResume();
new RetrieveBTCChartTask().execute("https://blockchain.info/charts/market-price?format=json");
/*LinearLayout layout = (LinearLayout) findViewById(R.id.chart);
if(m_chart == null)
{
initChart();
addSampleData();
m_chart = ChartFactory.getCubeLineChartView(this,m_dataset, m_renderer, 0.3f);
layout.addView(m_chart);
}
else
{
m_chart.repaint();
}*/
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.graph, menu);
return true;
}
class RetrieveBTCChartTask extends AsyncTask<String, Void, xyCoords[]>
{
@Override
protected xyCoords[] doInBackground(String... urls)
{
HttpClient httpclient = new DefaultHttpClient();
HttpGet httpget = new HttpGet(urls[0]);
httpget.setHeader("Content-type", "application/json");
//httppost.setHeader("qty", "1");
InputStream inputStream = null;
String result = null;
try
{
HttpResponse response = httpclient.execute(httpget);
HttpEntity entity = response.getEntity();
inputStream = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line= reader.readLine()) != null)
{
sb.append(line + "\n");
}
result = sb.toString();
}
catch (Exception e)
{}
finally
{
try
{
if(inputStream != null)
{
inputStream.close();
}
}
catch(Exception e)
{}
}
xyCoords[] coords = new xyCoords[5000];;
try
{
JSONObject btcPricesJSON = new JSONObject(result);
JSONArray prices = btcPricesJSON.getJSONArray("values");
if(prices != null)
{
int length = prices.length();
for(int i = 0; i < length; ++i)
{
JSONObject point = prices.getJSONObject(i);
coords[i].x = point.getDouble("x");
coords[i].y = point.getDouble("y");
}
}
}
catch(JSONException e)
{}
return coords;
}
@Override
protected void onPostExecute(xyCoords[] coords)
{
LinearLayout layout = (LinearLayout) findViewById(R.id.chart);
if(m_chart == null)
{
initChart();
addBtcPriceData(coords);
m_chart = ChartFactory.getCubeLineChartView(GraphActivity.this, m_dataset, m_renderer, 0.3f);
layout.addView(m_chart);
}
else
{
m_chart.repaint();
}
}
}
class xyCoords
{
public double x;
public double y;
}
}
06-21 23:52:18.288: E/AndroidRuntime(26917): FATAL EXCEPTION: AsyncTask #2
06-21 23:52:18.288: E/AndroidRuntime(26917): java.lang.RuntimeException: An error occured while executing doInBackground()
06-21 23:52:18.288: E/AndroidRuntime(26917): at android.os.AsyncTask$3.done(AsyncTask.java:299)
06-21 23:52:18.288: E/AndroidRuntime(26917): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
06-21 23:52:18.288: E/AndroidRuntime(26917): at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
06-21 23:52:18.288: E/AndroidRuntime(26917): at java.util.concurrent.FutureTask.run(FutureTask.java:239)
06-21 23:52:18.288: E/AndroidRuntime(26917): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
06-21 23:52:18.288: E/AndroidRuntime(26917): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
06-21 23:52:18.288: E/AndroidRuntime(26917): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
06-21 23:52:18.288: E/AndroidRuntime(26917): at java.lang.Thread.run(Thread.java:841)
06-21 23:52:18.288: E/AndroidRuntime(26917): Caused by: java.lang.NullPointerException
06-21 23:52:18.288: E/AndroidRuntime(26917): at info.lombardo.crypttrack.GraphActivity$RetrieveBTCChartTask.doInBackground(GraphActivity.java:149)
06-21 23:52:18.288: E/AndroidRuntime(26917): at info.lombardo.crypttrack.GraphActivity$RetrieveBTCChartTask.doInBackground(GraphActivity.java:1)
06-21 23:52:18.288: E/AndroidRuntime(26917): at android.os.AsyncTask$2.call(AsyncTask.java:287)
06-21 23:52:18.288: E/AndroidRuntime(26917): at java.util.concurrent.FutureTask.run(FutureTask.java:234)
06-21 23:52:18.288: E/AndroidRuntime(26917): ... 4 more
