我尝试使用json在后台工作后，我的应用程序崩溃了。我不知道为什么它不起作用。
类别：
package com.example.olda.hledac;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
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;
import android.widget.TextView;
import android.app.ListActivity;
import org.apache.http.NameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class vypis extends ListActivity {
private ProgressDialog pDialog;
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> uzivatele;
private static String url = "http://lokace.4fan.cz/vypis_uzivatelu.php";
private static final String TAG_SUCCESS = "success";
private static final String TAG_WP_USERS = "wp_users";
private static final String TAG_ID = "ID";
private static final String TAG_USER_login = "user_login";
JSONArray uziv = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_vypis);
ListView lv = getListView();
uzivatele = new ArrayList<HashMap<String, String>>();
new VypisUzivatele().execute();
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
String ID = ((TextView) view.findViewById(R.id.ID)).getText()
.toString();
Intent in = new Intent(getApplicationContext(),
MenuActivity.class);
in.putExtra(TAG_ID, ID);
startActivityForResult(in, 100);
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == 100) {
Intent intent = getIntent();
finish();
startActivity(intent);
}
}
class VypisUzivatele extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(vypis.this);
pDialog.setMessage("vypisování uživatelů");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args) {
List<NameValuePair> params = new ArrayList<NameValuePair>();
JSONObject json = jParser.makeHttpRequest(url, "GET", params);
Log.d("All Products: ", json.toString());
try {
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
uziv = json.getJSONArray(TAG_WP_USERS);
for (int i = 0; i < uziv.length(); i++) {
JSONObject c = uziv.getJSONObject(i);
String id = c.getString(TAG_ID);
String name = c.getString(TAG_USER_login);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_ID, id);
map.put(TAG_USER_login, name);
uzivatele.add(map);
}
} else {
Intent i = new Intent(getApplicationContext(),
MenuActivity.class);
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String file_url) {
pDialog.dismiss();
runOnUiThread(new Runnable() {
public void run() {
ListAdapter adapter = new SimpleAdapter(
vypis.this, uzivatele,
R.layout.activity_uzivatele, new String[] { TAG_ID,
TAG_USER_login},
new int[] { R.id.ID, R.id.name });
setListAdapter(adapter);
}
});
}
}
日志：
03-30 15:56:42.056 3999-4353/com.example.olda.hledac E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
Process: com.example.olda.hledac, PID: 3999
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
Caused by: java.lang.NullPointerException
at com.example.olda.hledac.vypis$VypisUzivatele.doInBackground(vypis.java:98)
at com.example.olda.hledac.vypis$VypisUzivatele.doInBackground(vypis.java:82)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
03-30 15:56:42.696 3999-3999/com.example.olda.hledac E/WindowManager﹕ android.view.WindowLeaked: Activity com.example.olda.hledac.vypis has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{41baf8f8 V.E..... R......D 0,0-684,192} that was originally added here
at android.view.ViewRootImpl.<init>(ViewRootImpl.java:370)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:248)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
at android.app.Dialog.show(Dialog.java:286)
at com.example.olda.hledac.vypis$VypisUzivatele.onPreExecute(vypis.java:91)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
at android.os.AsyncTask.execute(AsyncTask.java:535)
at com.example.olda.hledac.vypis.onCreate(vypis.java:51)
at android.app.Activity.performCreate(Activity.java:5395)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2162)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2248)
at android.app.ActivityThread.access$800(ActivityThread.java:138)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1199)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5072)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:780)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:596)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
在这种情况下我的网站主机出了问题。它们在每个页面上都包含了副词，而这个副词是用JSON发送的，这就是问题，并帮助我解决这个问题。我设置了子串，现在可以正常工作。
try {
jObj = new JSONObject(json.substring(3));
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data [" + e.getMessage()+"] "+json);
}