我知道有很多这样的问题，但我已经查看了所有这些问题，但没有一个答案对我有用。
这是我的java类
public class AllBugsActivity extends ListActivity {
private ProgressDialog pDialog;
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> bugsList;
private static String url_all_bugs = "http://10.0.2.2/FinalYearProject/FYPFinal/android_connect/get_all_bugs.php";
private static final String TAG_SUCCESS = "success";
private static final String TAG_BUGS = "bugs";
private static final String TAG_BID = "bid";
private static final String TAG_NAME = "name";
JSONArray bugs = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.all_bugs);
bugsList = new ArrayList<HashMap<String, String>>();
new LoadAllBugs().execute();
ListView lv = getListView();
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
String bid = ((TextView) view.findViewById(R.id.bid)).getText()
.toString();
Intent in = new Intent(getApplicationContext(),
EditBugActivity.class);
in.putExtra(TAG_BID, bid);
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 LoadAllBugs extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(AllBugsActivity.this);
pDialog.setMessage("Loading bugs. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args) {
List<NameValuePair> params = new ArrayList<NameValuePair>();
JSONObject json = jParser.makeHttpRequest(url_all_bugs, "GET", params);
Log.d("All Bugs: ", json.toString());
try {
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
bugs = json.getJSONArray(TAG_BUGS);
for (int i = 0; i < bugs.length(); i++) {
JSONObject c = bugs.getJSONObject(i);
String id = c.getString(TAG_BID);
String name = c.getString(TAG_NAME);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_BID, id);
map.put(TAG_NAME, name);
bugsList.add(map);
}
} else {
Intent i = new Intent(getApplicationContext(),
NewBugActivity.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(
AllBugsActivity.this, bugsList,
R.layout.list_bug, new String[] { TAG_BID,
TAG_NAME},
new int[] { R.id.bid, R.id.name });
setListAdapter(adapter);
}
});
}
}
}
这是我的 JSONParser 类
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
// function get json from url
// by making HTTP POST or GET mehtod
public JSONObject makeHttpRequest(String url, String method,
List<NameValuePair> params) {
// Making HTTP request
try {
// check for request method
if(method == "POST"){
// request method is POST
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
httpPost.setEntity(new UrlEncodedFormEntity(params));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}else if(method == "GET"){
// request method is GET
DefaultHttpClient httpClient = new DefaultHttpClient();
String paramString = URLEncodedUtils.format(params, "utf-8");
url += "?" + paramString;
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
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();
json = sb.toString();
} catch (Exception e) {
Log.e("Buffer Error", "Error converting result " + e.toString());
}
// try parse the string to a JSON object
try {
jObj = new JSONObject(json);
} catch (JSONException e) {
Log.e("JSON Parser", "Error parsing data " + e.toString());
}
// return JSON String
return jObj;
}
}
这是我收到的错误
03-21 17:06:15.158 1266-1280/com.example.neil.fypy4 E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:299)
at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
at java.lang.Thread.run(Thread.java:856)
Caused by: java.lang.NullPointerException
at com.example.neil.fypy4.AllBugsActivity$LoadAllBugs.doInBackground(AllBugsActivity.java:98)
at com.example.neil.fypy4.AllBugsActivity$LoadAllBugs.doInBackground(AllBugsActivity.java:83)
at android.os.AsyncTask$2.call(AsyncTask.java:287)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
at java.lang.Thread.run(Thread.java:856)
03-21 17:06:15.511 1266-1266/com.example.neil.fypy4 W/EGL_emulation﹕ eglSurfaceAttrib not implemented
03-21 17:06:16.008 1266-1266/com.example.neil.fypy4 E/WindowManager﹕ Activity com.example.neil.fypy4.AllBugsActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@41cd1748 that was originally added here
android.view.WindowLeaked: Activity com.example.neil.fypy4.AllBugsActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@41cd1748 that was originally added here
at android.view.ViewRootImpl.<init>(ViewRootImpl.java:374)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:292)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:224)
at android.view.WindowManagerImpl$CompatModeWrapper.addView(WindowManagerImpl.java:149)
at android.view.Window$LocalWindowManager.addView(Window.java:547)
at android.app.Dialog.show(Dialog.java:277)
at com.example.neil.fypy4.AllBugsActivity$LoadAllBugs.onPreExecute(AllBugsActivity.java:92)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
at android.os.AsyncTask.execute(AsyncTask.java:534)
at com.example.neil.fypy4.AllBugsActivity.onCreate(AllBugsActivity.java:50)
at android.app.Activity.performCreate(Activity.java:5008)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
我的 php 类(class)
<?php
$response = array();
require_once __DIR__ . '/db_connect.php';
$db = new DB_CONNECT();
$result = mysql_query("SELECT *FROM bugs") or die(mysql_error());
if (mysql_num_rows($result) > 0) {
$response["bugs"] = array();
while ($row = mysql_fetch_array($result)) {
$bug = array();
$bug["bid"] = $row["bid"];
$bug["name"] = $row["name"];
$bug["severity"] = $row["severity"];
$bug["description"] = $row["description"];
$bug["created_at"] = $row["created_at"];
$bug["updated_at"] = $row["updated_at"];
array_push($response["bugs"], $bug);
}
$response["success"] = 1;
echo json_encode($response);
} else {
$response["success"] = 0;
$response["message"] = "No bugs found";
echo json_encode($response);
}
?>
任何帮助将不胜感激。
最佳答案
因此，在堆栈跟踪中，它将向您显示行号:从中您可以在代码中对 NPE 的来源进行三角测量。由于您没有在这里提供行号，我将猜测 int success = json.getInt(TAG_SUCCESS);导致 NPE。原因是它是 doInBackground(...) 中第一个可能为 null 的对象。 --如果你看JSONParser上课了，你回来了jObj这是一个初始化为 null 的字段成员，并且仅在未发生错误时设置。也就是你没有 checkin doInBackground(...)是否JSONObject json从 = jParser.makeHttpRequest(url_all_bugs, "GET", params); 返回 null 或不返回 null而是依赖TAG_SUCCESS 。但这是先有鸡还是先有蛋的问题，因为如果失败，它可能为空，并且没有标签来检查是否成功!
无论如何，我的建议是添加 if (json != null)在 doInBackground(...) 中的 try/catch 之前。您可能会找到您的JSONParser类无法正确解析。您可以使用堆栈跟踪中的行号来查明问题的根源，或者仅使用调试器并逐步执行代码。
顺便说一下，您可以输入 public JSONObject makeHttpRequest(String url, String method, List<NameValuePair> params)静态方法，因为变量
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
不需要是类范围的(并且它们已经是静态的!)。只需让它们成为方法作用域并有一个方便的静态方法调用来解析你的 json 即可。
最后的评论:您不需要调用runOnUiThread(...)来自onPostExecute(...)因为onPostExecute(...)每个异步任务在 UI 线程上运行。这就是异步任务的工作原理。
关于java - 尝试将 MySQL 数据库连接到 android 时出现 NullPointerException 错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29185620/