我是Android新手并尝试制作简单的App。我写了一个测试程序，用于连接互联网并在我的应用程序中显示数据，但是当它想要连接时，该对象为空，程序崩溃，我不知道它为什么会发生？
码
package com.earthquake1;
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>();
private static final String TAG = "EARTHQUAKE";
private Handler handler = new Handler();
@Override
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
int layoutID = android.R.layout.simple_list_item_1;
aa = new ArrayAdapter<Quake>(this.getActivity(), layoutID ,earthquakes);
setListAdapter(aa);
Thread t = new Thread(new Runnable() {
@Override
public void run() {
refreshEarthquakes();
}
});
t.start();
}
protected void refreshEarthquakes() {
URL url;
try{
//String quakeFeed = getString(R.string.quake_feed);
url = new URL(getString(R.string.quake_feed));
URLConnection connection ;
connection = url.openConnection();
HttpURLConnection httpConnection = (HttpURLConnection) connection;
httpConnection.setAllowUserInteraction(false);
httpConnection.setInstanceFollowRedirects(true);
httpConnection.setRequestMethod("GET");
httpConnection.connect();
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("georss: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;
if(g != null)
point = g.getFirstChild().getNodeValue();
else
point = "";
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");
if(g != null){
l.setLatitude(Double.parseDouble(location[0]));
l.setLongitude(Double.parseDouble(location[1]));
}
else{
l.setLatitude(0);
l.setLongitude(0);
}
String magnitudeString = details.split(" ")[1];
int end = magnitudeString.length()-1;
double magnitude = 0;
if(!magnitudeString.equals("Feed")){
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() {
@Override
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,"ParserConfigurationException");
}
catch (SAXException e) {
Log.d(TAG,"SAXException");
}
catch(Exception e){
Log.d(TAG,e.getMessage());
}
finally {
}
}
protected void addNewQuake(Quake quake) {
earthquakes.add(quake);
aa.notifyDataSetChanged();
}
}
错误日志：
08-13 11:26:45.064: D/AndroidRuntime(31064): procName from cmdline: com.earthquake1
08-13 11:26:45.064: E/AndroidRuntime(31064): in writeCrashedAppName, pkgName :com.earthquake1
08-13 11:26:45.064: D/AndroidRuntime(31064): file written successfully with content: com.earthquake1 StringBuffer : ;com.earthquake1
08-13 11:26:45.064: E/AndroidRuntime(31064): FATAL EXCEPTION: main
08-13 11:26:45.064: E/AndroidRuntime(31064): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.earthquake1/com.earthquake1.Main}: android.view.InflateException: Binary XML file line #11: Error inflating class fragment
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.ActivityThread.access$600(ActivityThread.java:123)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.os.Handler.dispatchMessage(Handler.java:99)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.os.Looper.loop(Looper.java:137)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.ActivityThread.main(ActivityThread.java:4424)
08-13 11:26:45.064: E/AndroidRuntime(31064): at java.lang.reflect.Method.invokeNative(Native Method)
08-13 11:26:45.064: E/AndroidRuntime(31064): at java.lang.reflect.Method.invoke(Method.java:511)
08-13 11:26:45.064: E/AndroidRuntime(31064): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:825)
08-13 11:26:45.064: E/AndroidRuntime(31064): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:592)
08-13 11:26:45.064: E/AndroidRuntime(31064): at dalvik.system.NativeStart.main(Native Method)
08-13 11:26:45.064: E/AndroidRuntime(31064): Caused by: android.view.InflateException: Binary XML file line #11: Error inflating class fragment
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:697)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.view.LayoutInflater.rInflate(LayoutInflater.java:739)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
08-13 11:26:45.064: E/AndroidRuntime(31064): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:251)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.Activity.setContentView(Activity.java:1835)
08-13 11:26:45.064: E/AndroidRuntime(31064): at com.earthquake1.Main.onCreate(Main.java:12)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.Activity.performCreate(Activity.java:4465)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1051)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
08-13 11:26:45.064: E/AndroidRuntime(31064): ... 11 more
08-13 11:26:45.064: E/AndroidRuntime(31064): Caused by: android.app.Fragment$InstantiationException: Unable to instantiate fragment com.earthquake.EarthquakeListFragment: make sure class name exists, is public, and has an empty constructor that is public
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.Fragment.instantiate(Fragment.java:581)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.Fragment.instantiate(Fragment.java:549)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.Activity.onCreateView(Activity.java:4235)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:673)
08-13 11:26:45.064: E/AndroidRuntime(31064): ... 21 more
08-13 11:26:45.064: E/AndroidRuntime(31064): Caused by: java.lang.ClassNotFoundException: com.earthquake.EarthquakeListFragment
08-13 11:26:45.064: E/AndroidRuntime(31064): at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:61)
08-13 11:26:45.064: E/AndroidRuntime(31064): at java.lang.ClassLoader.loadClass(ClassLoader.java:501)
08-13 11:26:45.064: E/AndroidRuntime(31064): at java.lang.ClassLoader.loadClass(ClassLoader.java:461)
08-13 11:26:45.064: E/AndroidRuntime(31064): at android.app.Fragment.instantiate(Fragment.java:571)
08-13 11:26:45.064: E/AndroidRuntime(31064): ... 24 more
08-13 11:26:47.154: D/AndroidRuntime(31095): Shutting down VM
08-13 11:26:47.154: W/dalvikvm(31095): threadid=1: thread exiting with uncaught exception (group=0xb2c2d180)
08-13 11:26:47.164: D/AndroidRuntime(31095): procName from cmdline: com.earthquake1
08-13 11:26:47.164: E/AndroidRuntime(31095): in writeCrashedAppName, pkgName :com.earthquake1
答案 0 :(得分：2)
根本原因在于：
Caused by: java.lang.ClassNotFoundException: com.earthquake.EarthquakeListFragment
您的包名称似乎是com.earthquake1而不是com.earthquake。确保您的布局XML和代码在类和包名称上达成一致。
答案 1 :(得分：0)
无法实例化片段com.earthquake.EarthquakeListFragment：确保类名存在，是公共的，并且具有公共的空构造函数
制作EarthquakeListFragment的默认构造函数：
public EarthquakeListFragment(){
super();
}