我正在读取数据库并将其解析为Android上的listview。基本上，我已经使用PHP和MySQL设置了Web服务，现在正尝试将数据解析为android列表视图。我收到以下错误：
07-31 14:24:55.570: E/AndroidRuntime(846): FATAL EXCEPTION: AsyncTask #1
07-31 14:24:55.570: E/AndroidRuntime(846): Process: com.example.test, PID: 846
07-31 14:24:55.570: E/AndroidRuntime(846): java.lang.RuntimeException: An error occured while executing doInBackground()
07-31 14:24:55.570: E/AndroidRuntime(846): at android.os.AsyncTask$3.done(AsyncTask.java:300)
07-31 14:24:55.570: E/AndroidRuntime(846): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
07-31 14:24:55.570: E/AndroidRuntime(846): at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
07-31 14:24:55.570: E/AndroidRuntime(846): at java.util.concurrent.FutureTask.run(FutureTask.java:242)
07-31 14:24:55.570: E/AndroidRuntime(846): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
07-31 14:24:55.570: E/AndroidRuntime(846): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
07-31 14:24:55.570: E/AndroidRuntime(846): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
07-31 14:24:55.570: E/AndroidRuntime(846): at java.lang.Thread.run(Thread.java:841)
07-31 14:24:55.570: E/AndroidRuntime(846): Caused by: java.lang.NullPointerException
07-31 14:24:55.570: E/AndroidRuntime(846): at com.example.test.Menu.updateJSONdata(Menu.java:107)
07-31 14:24:55.570: E/AndroidRuntime(846): at com.example.test.Menu$LoadComments.doInBackground(Menu.java:189)
07-31 14:24:55.570: E/AndroidRuntime(846): at com.example.test.Menu$LoadComments.doInBackground(Menu.java:1)
07-31 14:24:55.570: E/AndroidRuntime(846): at android.os.AsyncTask$2.call(AsyncTask.java:288)
07-31 14:24:55.570: E/AndroidRuntime(846): at java.util.concurrent.FutureTask.run(FutureTask.java:237)
主类是：
package com.example.test;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
public class Menu extends ListActivity{
//Progress Dialog
private ProgressDialog pDialog;
// php read comments script
// testing on Emulator:
private static final String READ_COMMENTS_URL = "http://10.0.2.2:1337/webservice/lib.php";
// JSON IDS:
private static final String TAG_SUCCESS = "success";
private static final String TAG_TITLE = "title";
private static final String TAG_POSTS = "posts";
private static final String TAG_CALLING = "calling"; //calling
private static final String TAG_ACCESSION = "accession"; //accession
private static final String TAG_AUTHOR = "author"; //author
// An array of all of our comments
private JSONArray mComments = null;
// manages all of our comments in a list.
private ArrayList<HashMap<String, String>> mCommentList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// note that use read_comments.xml instead of our single_post.xml
setContentView(R.layout.menu);
}
@Override
protected void onResume() {
// TODO Auto-generated method stub
super.onResume();
// loading the comments via AsyncTask
new LoadComments().execute();
}
/*public void addComment(View v) {
Intent i = new Intent(ReadComments.this, AddComment.class);
startActivity(i);
} */
/**
* Retrieves recent post data from the server.
*/
public void updateJSONdata() {
mCommentList = new ArrayList<HashMap<String, String>>();
JSONParser jParser = new JSONParser();
JSONObject json = jParser.getJSONFromUrl(READ_COMMENTS_URL);
try {
mComments = json.getJSONArray(TAG_POSTS);
// looping through all posts according to the json object returned
for (int i = 0; i < mComments.length(); i++) {
JSONObject c = mComments.getJSONObject(i);
// gets the content of each tag
String title = c.getString(TAG_TITLE);
String author = c.getString(TAG_AUTHOR);
String accession = c.getString(TAG_ACCESSION);
String calling = c.getString(TAG_CALLING);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_TITLE, title);
map.put(TAG_AUTHOR, author);
map.put(TAG_ACCESSION, accession);
map.put(TAG_CALLING, calling);
// adding HashList to ArrayList
mCommentList.add(map);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
/**
* Inserts the parsed data into the listview.
*/
private void updateList() {
ListAdapter adapter = new SimpleAdapter(Menu.this, mCommentList,
R.layout.onepost, new String[] { TAG_TITLE, TAG_AUTHOR,
TAG_ACCESSION, TAG_CALLING }, new int[] { R.id.title, R.id.author,
R.id.accession, R.id.calling });
setListAdapter(adapter);
ListView lv = getListView();
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
}
});
}
public class LoadComments extends AsyncTask<Void, Void, Boolean> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(Menu.this);
pDialog.setMessage("Loading Comments...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
@Override
protected Boolean doInBackground(Void... arg0) {
updateJSONdata();
return null;
}
@Override
protected void onPostExecute(Boolean result) {
super.onPostExecute(result);
pDialog.dismiss();
updateList();
}
}
}
最佳答案
我已经完成2节课来获取http请求结果。很好用。
BasicHttpRequest.java
public class BasicHttpRequest
{
private JSONObject _result = null;
private int _err = -1;
private String _errMessage = null;
private HttpRequestBase _request = null;
private String _requestError = null;
private UrlBuilder _urlBuilder = null;
public BasicHttpRequest(RequestType requestType, UrlBuilder urlBuilder)
{
this._urlBuilder = urlBuilder;
if (requestType.equals(RequestType.POST))
this.createPostRequest();
if (requestType.equals(RequestType.GET))
this.createGetRequest();
}
private void createPostRequest()
{
HttpPost post = new HttpPost(this._urlBuilder.getUrlBase());
try
{
post.setEntity(new UrlEncodedFormEntity(this._urlBuilder.getArrayList()));
} catch (UnsupportedEncodingException e)
{
e.printStackTrace();
return;
}
this._request = post;
}
private void createGetRequest()
{
HttpGet get = new HttpGet(this._urlBuilder.getUrl());
this._request = get;
}
/**
* This function executes the request passed by the constructor.
* @return Returns false if an error occurred, true otherwise. For more informations about the error, use getRequestError.
*/
public boolean executeRequest()
{
InputStream iStream = null;
String result = "";
try
{
HttpClient httpclient = new DefaultHttpClient();
HttpResponse response = httpclient.execute(this._request);
HttpEntity entity = response.getEntity();
iStream = entity.getContent();
} catch (Exception e)
{
Log.e("ReqError", "[Error in HTTP Connection] : " + e.toString());
this._requestError = ErrorMessage.CONNECTION_ERROR;
return false;
}
try
{
BufferedReader reader = new BufferedReader(new InputStreamReader(iStream, "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)
{
Log.e("ConversionError", "[Error while converting result] : " + e.toString());
this._requestError = ErrorMessage.DATA_ERROR;
return false;
}
JSONObject jObject;
try
{
jObject = new JSONObject(result);
this._err = jObject.getInt("err");
this._errMessage = jObject.getString("errMessage");
} catch (JSONException e)
{
Log.e("JSONError", "[Error parsing data] : " + e.toString());
this._requestError = ErrorMessage.DATA_ERROR;
return false;
}
this._result = jObject;
return true;
}
public String getValueForKey(String key)
{
String value = null;
if (this._result == null)
return null;
try
{
value = this._result.getString(key);
} catch (JSONException e)
{
e.printStackTrace();
return null;
}
if (value.equals("null"))
return null;
return value;
}
public boolean hasError()
{
if (this._err == 0)
return false;
return true;
}
public String getErrMessage()
{
return this._errMessage;
}
public JSONObject getResult()
{
return this._result;
}
/**
* This function gives you the reason of the request error.
* @return Returns an error message if an error occurred during the request execution, null otherwise.
*/
public String getRequestError()
{
return this._requestError;
}
}
UrlBuilder.java
public class UrlBuilder
{
private String _urlBase;
private HashMap<String, String> _urlArgs;
public UrlBuilder(String urlBase)
{
this._urlArgs = new HashMap<String, String>();
this._urlBase = urlBase;
}
public UrlBuilder addArgument(String name, String value)
{
this._urlArgs.put(name, value);
return this;
}
public void removeArgument(String name)
{
this._urlArgs.remove(name);
}
public boolean argumentExists(String name)
{
return this._urlArgs.containsKey(name);
}
public String getUrl()
{
int i = 0;
String url = this._urlBase;
for (Map.Entry<String, String> entry : this._urlArgs.entrySet())
{
url += (i == 0 ? "?" : "&");
try
{
url += URLEncoder.encode(entry.getKey(), "UTF-8") + "=" + URLEncoder.encode(entry.getValue(), "UTF-8");
} catch (UnsupportedEncodingException e)
{
Log.e("UrlEncoder", "Error while trying to encode URL");
e.printStackTrace();
}
i++;
}
return url;
}
public String getUrlBase()
{
return this._urlBase;
}
public List<NameValuePair> getArrayList()
{
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
for (Map.Entry<String, String> entry : this._urlArgs.entrySet())
{
nameValuePairs.add(new BasicNameValuePair(entry.getKey(), entry.getValue()));
}
return nameValuePairs;
}
}
只需使用服务器URL库（例如“ http://api.yoursite.fr/page”）实例化UrlBuilder，然后使用addArgument方法添加参数。然后，使用先前的UrlBuilder实例和请求类型实例化BasicHttpRequest对象（它只是具有POST和GET的Enum）。最后，使用BasicHttpRequest方法getValueForKey获取结果。
问我有没有问题。
希望能帮助到你。