java - 我的每个 JSONfunction 相关程序突然发生同样的错误是 NullPointerException 我如何解决它？
问题描述
在 MainActivity.java 文件中出现在线错误
新的 DownloadJSON().execute(); jsonarray = jsonobject.getJSONArray("worldpopulation");
每个程序中都没有获取任何数组，我的数据库字段值已经是当前的。但是这一行错误空指针异常。
MainActivity.java
package com.androidbegin.jsonparsetutorial;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
public class MainActivity extends Activity {
// Declare Variables
JSONObject jsonobject;
JSONArray jsonarray;
ListView listview;
ListViewAdapter adapter;
ProgressDialog mProgressDialog;
ArrayList<HashMap<String, String>> arraylist;
static String RANK = "rank";
static String COUNTRY = "country";
static String POPULATION = "population";
static String FLAG = "flag";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listview_main);
new DownloadJSON().execute();
}
// DownloadJSON AsyncTask
private class DownloadJSON extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
mProgressDialog = new ProgressDialog(MainActivity.this);
mProgressDialog.setTitle("Android JSON Parse Tutorial");
mProgressDialog.setMessage("Loading...");
mProgressDialog.setIndeterminate(false);
mProgressDialog.show();
}
@Override
protected Void doInBackground(Void... params) {
arraylist = new ArrayList<HashMap<String, String>>();
jsonobject = JSONfunctions.getJSONfromURL("https://www.androidbegin.com/
tutorial/jsonparsetutorial.txt");
try {
// Locate the array name in JSON
jsonarray = jsonobject.getJSONArray("worldpopulation");
for (int i = 0; i < jsonarray.length(); i++) {
HashMap<String, String> map = new HashMap<String, String> ();
jsonobject = jsonarray.getJSONObject(i);
// Retrive JSON Objects
map.put("rank", jsonobject.getString("rank"));
map.put("country", jsonobject.getString("country"));
map.put("population", jsonobject.getString("population"));
map.put("flag", jsonobject.getString("flag"));
// Set the JSON Objects into the array
arraylist.add(map);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args) {
// Locate the listview in listview_main.xml
listview = (ListView) findViewById(R.id.listview);
// Pass the results into ListViewAdapter.java
adapter = new ListViewAdapter(MainActivity.this, arraylist);
// Set the adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
mProgressDialog.dismiss();
}
}
}
我的每个 JSON 函数相关的程序突然发生同样的错误是 NullPointerException。之前这个错误没有发生。我如何解决它？我使用 Eclipse Juno
我在我的程序中使用了我的 JSONfunctions.java 类文件
JSONfunctions.java
public class JSONfunctions {
public static JSONObject getJSONfromURL(String url) {
InputStream is = null;
String result = "";
JSONObject jArray = null;
// Download JSON data from URL
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(url);
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection " + e.toString());
}
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
try {
jArray = new JSONObject(result);
} catch (JSONException e) {
Log.e("log_tag", "Error parsing data " + e.toString());
}
return jArray;
}
}
日志错误：
10-15 18:25:49.835: E/(3836): appName=com.androidbegin.jsonparsetutorial,
acAppName=/system/bin/surfaceflinger
10-15 18:25:49.835: E/(3836): 0
10-15 18:25:49.926: E/log_tag(3836): Error in http connection
java.net.UnknownHostException: Unable to resolve host
"www.androidbegin.com": No address associated with hostname
10-15 18:25:49.926: E/log_tag(3836): Error converting result
java.lang.NullPointerException: lock == null
10-15 18:25:49.926: E/log_tag(3836): Error parsing data
org.json.JSONException: End of input at character 0 of
10-15 18:25:49.930: E/AndroidRuntime(3836): FATAL EXCEPTION: AsyncTask #1
10-15 18:25:49.930: E/AndroidRuntime(3836): Process:
com.androidbegin.jsonparsetutorial, PID: 3836
10-15 18:25:49.930: E/AndroidRuntime(3836): java.lang.RuntimeException: An
error occured while executing doInBackground()
10-15 18:25:49.930: E/AndroidRuntime(3836): at
android.os.AsyncTask$3.done(AsyncTask.java:300)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
java.util.concurrent.FutureTask.setException(FutureTask.java:222)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
java.util.concurrent.FutureTask.run(FutureTask.java:242)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
java.util.concurrent.ThreadPoolExecutor.runWorker
(ThreadPoolExecutor.java:1112)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
java.util.concurrent.ThreadPoolExecutor$Worker.run
(ThreadPoolExecutor.java:587)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
java.lang.Thread.run(Thread.java:841)
10-15 18:25:49.930: E/AndroidRuntime(3836): Caused by:
java.lang.NullPointerException
10-15 18:25:49.930: E/AndroidRuntime(3836): at
com.androidbegin.jsonparsetutorial.
MainActivity$DownloadJSON.doInBackground(MainActivity.java:64)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
com.androidbegin.jsonparsetutorial.
MainActivity$DownloadJSON.doInBackground(MainActivity.java:1)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
android.os.AsyncTask$2.call(AsyncTask.java:288)
10-15 18:25:49.930: E/AndroidRuntime(3836): at
java.util.concurrent.FutureTask.run(FutureTask.java:237)
10-15 18:25:49.930: E/AndroidRuntime(3836): ... 4 more
10-15 18:25:50.453: E/WindowManager(3836): android.view.WindowLeaked:
Activity com.androidbegin.jsonparsetutorial.
MainActivity has leaked window
com.android.internal.policy.impl.PhoneWindow$DecorView
{41f618c8 V.E..... R.....ID 0,0-480,269} that was
originally added here
10-15 18:25:50.453: E/WindowManager(3836): at android.view.ViewRootImpl.
<init>(ViewRootImpl.java:422)
10-15 18:25:50.453: E/WindowManager(3836): at
android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:250)
10-15 18:25:50.453: E/WindowManager(3836): at
android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
10-15 18:25:50.453: E/WindowManager(3836): at
android.app.Dialog.show(Dialog.java:286)
10-15 18:25:50.453: E/WindowManager(3836): at
com.androidbegin.jsonparsetutorial.
MainActivity$DownloadJSON.onPreExecute(MainActivity.java:51)
10-15 18:25:50.453: E/WindowManager(3836): at
android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
10-15 18:25:50.453: E/WindowManager(3836): at
android.os.AsyncTask.execute(AsyncTask.java:535)
10-15 18:25:50.453: E/WindowManager(3836): at
com.androidbegin.jsonparsetutorial.
MainActivity.onCreate(MainActivity.java:34)
10-15 18:25:50.453: E/WindowManager(3836): at
android.app.Activity.performCreate(Activity.java:5264)
10-15 18:25:50.453: E/WindowManager(3836): at
android.app.Instrumentation.callActivityOnCreate
(Instrumentation.java:1088)
10-15 18:25:50.453: E/WindowManager(3836): at
android.app.ActivityThread.performLaunchActivity
(ActivityThread.java:2302)
10-15 18:25:50.453: E/WindowManager(3836): at
android.app.ActivityThread.handleLaunchActivity
(ActivityThread.java:2390)
10-15 18:25:50.453: E/WindowManager(3836): at
android.app.ActivityThread.access$800
(ActivityThread.java:151)
10-15 18:25:50.453: E/WindowManager(3836): at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
10-15 18:25:50.453: E/WindowManager(3836): at
android.os.Handler.dispatchMessage(Handler.java:110)
10-15 18:25:50.453: E/WindowManager(3836): at
android.os.Looper.loop(Looper.java:193)
10-15 18:25:50.453: E/WindowManager(3836): at
android.app.ActivityThread.main(ActivityThread.java:5292)
10-15 18:25:50.453: E/WindowManager(3836): at
java.lang.reflect.Method.invokeNative(Native Method)
10-15 18:25:50.453: E/WindowManager(3836): at
java.lang.reflect.Method.invoke(Method.java:515)
10-15 18:25:50.453: E/WindowManager(3836): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run
(ZygoteInit.java:824)
10-15 18:25:50.453: E/WindowManager(3836): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:640)
10-15 18:25:50.453: E/WindowManager(3836): at
dalvik.system.NativeStart.main(Native Method)
解决方案
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