Chapter 6 - Earthquake App Example

uler3161 · December 1st, 2013, 11:08 PM

I'm 99% sure that reinstalling software isn't going to fix this. Could you post what is on line 95? And I assume this is the code in chapter 6?

Markstar · December 8th, 2013, 06:21 PM

Quote:

Originally Posted by uler3161

I'm 99% sure that reinstalling software isn't going to fix this. Could you post what is on line 95? And I assume this is the code in chapter 6?

Hi,
sorry for the delayed answer. I was waiting for my Android phone to do some more testing and to see if it was something on my end. But I still get the same error message (other examples I have tried work, though).

Here are the error lines:

Code:

47: refreshEarthquakes();   // inside the Thread
55: private void refreshEarthquakes() {
95: String point = g.getFirstChild().getNodeValue();

uler3161 · December 8th, 2013, 06:34 PM

I haven't looked at the data feed, but my gut feeling says that it has changed. I'm looking at page 208 of the book and see that g is a georss:point element within an entry element. And apparently either g is null or g.getFirstChild() returns null. If it were me, I'd try to view the document returned by that url to see if there are any georss:point elements within an entry element. And if so, see if there is a child within the georss:point element.

r6cer · December 9th, 2013, 04:03 PM

Hello!
I've got a problem with the "earthquake example"-code. When I am debugging the source code, the debugger throws a NullPointerException. I hope that you can help me.

I've marked the critical lines for you. Thanks!

That's the code:

Code:

package com.example.earthquake;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.GregorianCalendar;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

import android.annotation.SuppressLint;
import android.location.Location;
import android.os.Bundle;
import android.os.Handler;

import android.util.Log;
import android.widget.ArrayAdapter;

@SuppressLint("SimpleDateFormat")
public class EarthquakeListFragment extends android.app.ListFragment {

ArrayAdapter<Quake> aa;
ArrayList<Quake> earthquakes = new ArrayList<Quake>();

private static final String TAG = "EARTHQUAKE";
private Handler handler = new Handler();

public void refreshEarthquakes() {
URL url;
try {
String quakeFeed = getString(R.string.quake_feed);
url = new URL(quakeFeed);

URLConnection connection;
connection = url.openConnection();

HttpURLConnection httpConnection = (HttpURLConnection) connection;
int responseCode = httpConnection.getResponseCode();

if (responseCode == HttpURLConnection.HTTP_OK) {
	InputStream in = httpConnection.getInputStream();

	DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
	DocumentBuilder db = dbf.newDocumentBuilder();

	Document dom = db.parse(in);
	Element docEle = dom.getDocumentElement();

	earthquakes.clear();

	NodeList nl = docEle.getElementsByTagName("entry");
	if (nl != null && nl.getLength() > 0) {
		for (int i = 0; i < nl.getLength(); i++) {
			Element entry = (Element) nl.item(i);
			Element title = (Element) entry.getElementsByTagName("title").item(0);
			Element g = (Element) entry.getElementsByTagName("georrs:point").item(0);
			Element when = (Element) entry.getElementsByTagName("updated").item(0);
			Element link = (Element) entry.getElementsByTagName("link").item(0);

			String details = title.getFirstChild().getNodeValue();
			String hostname = "http://earthquake.usgs.gov";
			String linkString = hostname + link.getAttribute("href");

			String point = g.getFirstChild().getNodeValue();
			String dt = when.getFirstChild().getNodeValue();
			SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'hh:mm:ss'Z'");
			Date qdate = new GregorianCalendar(0, 0, 0).getTime();
			try {
				qdate = sdf.parse(dt);
			} catch (ParseException e) {
				Log.d(TAG, "Date parsing exception.", e);
			}

			String[] location = point.split(" ");
			Location l = new Location("dummyGPS");
			l.setLatitude(Double.parseDouble(location[0]));
			l.setLongitude(Double.parseDouble(location[1]));

			String magnitudeString = details.split(" ")[1];
			int end = magnitudeString.length() - 1;
			double magnitude = Double.parseDouble(magnitudeString.substring(0, end));
			details = details.split(",")[1].trim();
			
			final Quake quake = new Quake(qdate, details, l,magnitude, linkString);
			
			handler.post(new Runnable() {
				public void run() {
					addNewQuake(quake);
					}
				});

			}
		}
	}
} catch (MalformedURLException e) {
	Log.d(TAG, "MalformedURLException");
} catch (IOException e) {
	Log.d(TAG, "IOException");
} catch (ParserConfigurationException e) {
	Log.d(TAG, "Parser Configuration Exception");
} catch (SAXException e) {
	Log.d(TAG, "SAX Exception");
} finally {
}
}

	private void addNewQuake(Quake _quake) {
		earthquakes.add(_quake);
		aa.notifyDataSetChanged();
	}

	@Override
	public void onActivityCreated(Bundle savedInstanceState) {
		super.onActivityCreated(savedInstanceState);

		int layoutID = android.R.layout.simple_list_item_1;
		aa = new ArrayAdapter<Quake>(getActivity(), layoutID, earthquakes);
		setListAdapter(aa);

		Thread t = new Thread(new Runnable() {
			public void run() {
				refreshEarthquakes();
			}
		});
		t.start();
	}
}

uler3161 · December 9th, 2013, 04:15 PM

Quote:

Originally Posted by r6cer

Hello!
I've got a problem with the "earthquake example"-code. When I am debugging the source code, the debugger throws a NullPointerException. I hope that you can help me.

I've marked the critical lines for you. Thanks!

Same issue that Markstar is having. I looked at the xml manually and it looked ok, so I'm not sure what is wrong. I would suggest dumping the contents retrieved from the stream into the log and see what it looks like.

BretAntilles · December 9th, 2013, 05:17 PM

The problem is that the weblink of the Earthquake Hazards Program refers to a deprecated representation. For the example this is no problem, but the first element in the xml file notifies the user that the xml-file is deprecated. This element cannot be parsed correctly with the result, that a Null-Pointer exception is thrown. You can solve this problem by starting the loop at i=1. Here the correct code for the EarthquakeListFragment.java:

Code:

package com.paad.earthquake;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.GregorianCalendar;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

import android.app.ListFragment;
import android.location.Location;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.widget.ArrayAdapter;

public class EarthquakeListFragment extends ListFragment {

	ArrayAdapter<Quake> aa;
	ArrayList<Quake> earthquakes = new ArrayList<Quake>();

	@Override
	public void onActivityCreated(Bundle savedInstanceState) {
		super.onActivityCreated(savedInstanceState);

		int layoutID = android.R.layout.simple_list_item_1;
		aa = new ArrayAdapter<Quake>(getActivity(), layoutID, earthquakes);
		setListAdapter(aa);

		Thread t = new Thread(new Runnable() {
			public void run() {
				refreshEarthquakes();
			}
		});
		t.start();
	}

	private static final String TAG = "EARTHQUAKE";
	private Handler handler = new Handler();

	private void refreshEarthquakes() {
		// Get the XML
		URL url;
		try {
			String quakeFeed = getString(R.string.quake_feed);
			url = new URL(quakeFeed);

			URLConnection connection;
			connection = url.openConnection();

			HttpURLConnection httpConnection = (HttpURLConnection) connection;
			int responseCode = httpConnection.getResponseCode();

			if (responseCode == HttpURLConnection.HTTP_OK) {
				InputStream in = httpConnection.getInputStream();

				DocumentBuilderFactory dbf = DocumentBuilderFactory
						.newInstance();
				DocumentBuilder db = dbf.newDocumentBuilder();

				// Parse the earthquake feed.
				Document dom = db.parse(in);
				Element docEle = dom.getDocumentElement();

				// Clear the old earthquakes
				earthquakes.clear();

				// Get a list of each earthquake entry.
				NodeList nl = docEle.getElementsByTagName("entry");
				if (nl != null && nl.getLength() > 0) {
					for (int i = 1; i < nl.getLength(); i++) {
						Element entry = (Element) nl.item(i);
						Element title = (Element) entry.getElementsByTagName(
								"title").item(0);
						Element when = (Element) entry.getElementsByTagName(
								"updated").item(0);
						Element link = (Element) entry.getElementsByTagName(
								"link").item(0);

						String details = title.getFirstChild().getNodeValue();
						String hostname = "http://earthquake.usgs.gov";
						String linkString = hostname
								+ link.getAttribute("href");

						String dt = when.getFirstChild().getNodeValue();
						SimpleDateFormat sdf = new SimpleDateFormat(
								"yyyy-MM-dd'T'hh:mm:ss'Z'");
						Date qdate = new GregorianCalendar(0, 0, 0).getTime();
						try {
							qdate = sdf.parse(dt);
						} catch (ParseException e) {
							Log.d(TAG, "Date parsing exception.", e);
						}

						Location l = new Location("dummyGPS");

						String magnitudeString = details.split(" ")[1];
						int end = magnitudeString.length() - 1;
						double magnitude = Double.parseDouble(magnitudeString
								.substring(0, end));

						details = details.split(",")[1].trim();

						final Quake quake = new Quake(qdate, details, l,
								magnitude, linkString);

						// Process a newly found earthquake
						handler.post(new Runnable() {
							
							public void run() {
								addNewQuake(quake);

							}
						});
					}
				}
			}
		} catch (MalformedURLException e) {
			Log.d(TAG, "MalformedURLException", e);
		} catch (IOException e) {
			Log.d(TAG, "IOException", e);
		} catch (ParserConfigurationException e) {
			Log.d(TAG, "Parser Configuration Exception", e);
		} catch (SAXException e) {
			Log.d(TAG, "SAX Exception", e);
		} finally {
		}
	}

	private void addNewQuake(Quake _quake) {
		// Add the new quake to our list of earthquakes.
		earthquakes.add(_quake);

		// Notify the array adapter of a change.
		aa.notifyDataSetChanged();
	}

}

Markstar · December 18th, 2013, 07:54 AM

Thank you, that works!

So the Handler is there to manage the thread?

Also, I noticed that you removed the geolocation. Any particular reason for that (other than that is not used in this example)?

LeBoeuf · January 16th, 2014, 05:19 AM

Thank you for the solution. Now it works fine.

coolbud012 · June 3rd, 2014, 02:42 PM

Quote:

Originally Posted by BretAntilles

The problem is that the weblink of the Earthquake Hazards Program refers to a deprecated representation. For the example this is no problem, but the first element in the xml file notifies the user that the xml-file is deprecated. This element cannot be parsed correctly with the result, that a Null-Pointer exception is thrown. You can solve this problem by starting the loop at i=1. Here the correct code for the EarthquakeListFragment.java:

Code:

package com.paad.earthquake;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.GregorianCalendar;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

import android.app.ListFragment;
import android.location.Location;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.widget.ArrayAdapter;

public class EarthquakeListFragment extends ListFragment {

	ArrayAdapter<Quake> aa;
	ArrayList<Quake> earthquakes = new ArrayList<Quake>();

	@Override
	public void onActivityCreated(Bundle savedInstanceState) {
		super.onActivityCreated(savedInstanceState);

		int layoutID = android.R.layout.simple_list_item_1;
		aa = new ArrayAdapter<Quake>(getActivity(), layoutID, earthquakes);
		setListAdapter(aa);

		Thread t = new Thread(new Runnable() {
			public void run() {
				refreshEarthquakes();
			}
		});
		t.start();
	}

	private static final String TAG = "EARTHQUAKE";
	private Handler handler = new Handler();

	private void refreshEarthquakes() {
		// Get the XML
		URL url;
		try {
			String quakeFeed = getString(R.string.quake_feed);
			url = new URL(quakeFeed);

			URLConnection connection;
			connection = url.openConnection();

			HttpURLConnection httpConnection = (HttpURLConnection) connection;
			int responseCode = httpConnection.getResponseCode();

			if (responseCode == HttpURLConnection.HTTP_OK) {
				InputStream in = httpConnection.getInputStream();

				DocumentBuilderFactory dbf = DocumentBuilderFactory
						.newInstance();
				DocumentBuilder db = dbf.newDocumentBuilder();

				// Parse the earthquake feed.
				Document dom = db.parse(in);
				Element docEle = dom.getDocumentElement();

				// Clear the old earthquakes
				earthquakes.clear();

				// Get a list of each earthquake entry.
				NodeList nl = docEle.getElementsByTagName("entry");
				if (nl != null && nl.getLength() > 0) {
					for (int i = 1; i < nl.getLength(); i++) {
						Element entry = (Element) nl.item(i);
						Element title = (Element) entry.getElementsByTagName(
								"title").item(0);
						Element when = (Element) entry.getElementsByTagName(
								"updated").item(0);
						Element link = (Element) entry.getElementsByTagName(
								"link").item(0);

						String details = title.getFirstChild().getNodeValue();
						String hostname = "http://earthquake.usgs.gov";
						String linkString = hostname
								+ link.getAttribute("href");

						String dt = when.getFirstChild().getNodeValue();
						SimpleDateFormat sdf = new SimpleDateFormat(
								"yyyy-MM-dd'T'hh:mm:ss'Z'");
						Date qdate = new GregorianCalendar(0, 0, 0).getTime();
						try {
							qdate = sdf.parse(dt);
						} catch (ParseException e) {
							Log.d(TAG, "Date parsing exception.", e);
						}

						Location l = new Location("dummyGPS");

						String magnitudeString = details.split(" ")[1];
						int end = magnitudeString.length() - 1;
						double magnitude = Double.parseDouble(magnitudeString
								.substring(0, end));

						details = details.split(",")[1].trim();

						final Quake quake = new Quake(qdate, details, l,
								magnitude, linkString);

						// Process a newly found earthquake
						handler.post(new Runnable() {
							
							public void run() {
								addNewQuake(quake);

							}
						});
					}
				}
			}
		} catch (MalformedURLException e) {
			Log.d(TAG, "MalformedURLException", e);
		} catch (IOException e) {
			Log.d(TAG, "IOException", e);
		} catch (ParserConfigurationException e) {
			Log.d(TAG, "Parser Configuration Exception", e);
		} catch (SAXException e) {
			Log.d(TAG, "SAX Exception", e);
		} finally {
		}
	}

	private void addNewQuake(Quake _quake) {
		// Add the new quake to our list of earthquakes.
		earthquakes.add(_quake);

		// Notify the array adapter of a change.
		aa.notifyDataSetChanged();
	}

}

Seems you have removed : georss:point

There isnt any way to do it by keeping that code itself...