【发布时间】：2013-07-28 15:16:28
【问题描述】：
我的应用程序仍在崩溃，但现在它给了我致命异常：AsyncTask #3。我一直在查看我的代码几个小时，但我无法找出它崩溃的原因。所以我只是希望有人能告诉我为什么以及我可以解决它。
07-28 14:50:19.728: E/AndroidRuntime(776): FATAL EXCEPTION: AsyncTask #3
07-28 14:50:19.728: E/AndroidRuntime(776): java.lang.RuntimeException: An error occured while executing doInBackground()
07-28 14:50:19.728: E/AndroidRuntime(776): at android.os.AsyncTask$3.done(AsyncTask.java:299)
07-28 14:50:19.728: E/AndroidRuntime(776): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
07-28 14:50:19.728: E/AndroidRuntime(776): at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
07-28 14:50:19.728: E/AndroidRuntime(776): at java.util.concurrent.FutureTask.run(FutureTask.java:239)
07-28 14:50:19.728: E/AndroidRuntime(776): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
07-28 14:50:19.728: E/AndroidRuntime(776): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
07-28 14:50:19.728: E/AndroidRuntime(776): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
07-28 14:50:19.728: E/AndroidRuntime(776): at java.lang.Thread.run(Thread.java:856)
07-28 14:50:19.728: E/AndroidRuntime(776): Caused by: java.lang.NullPointerException
07-28 14:50:19.728: E/AndroidRuntime(776): at com.theproblemsolver.ListView$LoadAllData.doInBackground(ListView.java:92)
07-28 14:50:19.728: E/AndroidRuntime(776): at com.theproblemsolver.ListView$LoadAllData.doInBackground(ListView.java:1)
07-28 14:50:19.728: E/AndroidRuntime(776): at android.os.AsyncTask$2.call(AsyncTask.java:287)
07-28 14:50:19.728: E/AndroidRuntime(776): ... 4 more
主活动
public class MainActivity extends Activity {
EditText et;
Button getanswer;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button getanswer = (Button) findViewById(R.id.button1);
getanswer.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent i = new Intent(MainActivity.this, ListView.class);
startActivity(i);
}
});
}
}
ListView 活动
public class ListView extends ListActivity {
private ProgressDialog pDialog;
JSONParsser jParser = new JSONParsser();
ArrayList<HashMap<String, String>> questionList;
private static String URI = "http://example.com/json";;
//JSONObject json = jParser.getJSONFromURI(URI);
final String TAG_RESULTS = "ResultsSet";
final String TAG_SUBJECT = "Subject";
final String TAG_NUMANSWERS = "NumAnswers";
final String TAG_QUESTION = "Question";
final String TAG_QUESTION_CONTENT = "Content";
final String TAG_QUESTION_CHOSENANSWER = "ChosenAnswer";
final String TAG_QUESTION_ANSWERS = "Answers";
JSONArray ResultsSet = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.listview);
questionList = new ArrayList<HashMap<String, String>>();
android.widget.ListView lv = getListView();
new LoadAllData().execute();
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,int position, long id) {
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == 100) {
Intent intent = getIntent();
startActivity(intent);
finish();
}
}
class LoadAllData extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(ListView.this);
pDialog.setMessage("Loading Data. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args) {
try {
JSONObject json = jParser.getJSONFromURI(URI);
ResultsSet = json.getJSONArray(TAG_RESULTS);
for(int i = 0; i < ResultsSet.length(); i++) {
JSONObject r = ResultsSet.getJSONObject(i);
String Subject = r.getString(TAG_SUBJECT);
String NumAnswers = r.getString(TAG_NUMANSWERS);
JSONObject Question = r.getJSONObject(TAG_QUESTION);
String Content = Question.getString(TAG_QUESTION_CONTENT);
String ChosenAnswer = Question.getString(TAG_QUESTION_CHOSENANSWER);
String Answers = Question.getString(TAG_QUESTION_ANSWERS);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_SUBJECT, Subject);
map.put(TAG_NUMANSWERS, NumAnswers);
questionList.add(map);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(String file_URI) {
pDialog.closeOptionsMenu();
runOnUiThread(new Runnable() {
public void run() {
ListAdapter adapter = new SimpleAdapter(getBaseContext(), questionList,
R.layout.row,
new String[] { TAG_SUBJECT, TAG_NUMANSWERS }, new int[] {
R.id.Subject, R.id.NumAnswers });
setListAdapter(adapter);
}
});
}
}}
JSONParsser 类
public class JSONParsser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
EditText et;
public JSONParsser () {
}
public JSONObject getJSONFromURI(String URI) {
try{
HttpClient client = new DefaultHttpClient();
try {
URI website = new URI("http://example.com/json");
HttpGet request = new HttpGet();
request.setURI(website);
try {
HttpResponse response = client.execute(request);
HttpEntity httpEntity = response.getEntity();
is = httpEntity.getContent();
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} catch (URISyntaxException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return jObj;
}finally{}
}{
}
}
如果您对我的代码崩溃的原因和其他可能的错误有任何想法，请告诉我。
【问题讨论】：
-
您在 doInBackground() 的第 92 行取消引用空指针。我不会数行来确定是哪一行。似乎您的 JSON 缺少您期望它拥有的数据，或者您根本没有得到它。
-
第 92 行是
for(int i = 0; i < ResultsSet.length(); i++) { -
所以 ResultsSet 必须为空。这意味着 TAG_RESULTS 不在服务的 JSON 中。
-
好的，我得检查一下，但第 39 行也有问题吗？
JSONArray ResultsSet = null;
标签： android json android-listview android-asynctask