我是AsyncTask的新手，所以我遇到了一些错误。我只是告诉我出了什么问题以及我需要做些什么来解决它。我得到一个致命的异常：AsyncTask＃1每次我尝试这个代码，所以有人可以帮助我。
07-25 03:47:57.526: W/dalvikvm(799): threadid=11: thread exiting with uncaught exception (group=0x40a71930)
07-25 03:47:57.666: E/AndroidRuntime(799): FATAL EXCEPTION: AsyncTask #1
07-25 03:47:57.666: E/AndroidRuntime(799): java.lang.RuntimeException: An error occured while executing doInBackground()
07-25 03:47:57.666: E/AndroidRuntime(799): at android.os.AsyncTask$3.done(AsyncTask.java:299)
07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.FutureTask.run(FutureTask.java:239)
07-25 03:47:57.666: E/AndroidRuntime(799): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
07-25 03:47:57.666: E/AndroidRuntime(799): at java.lang.Thread.run(Thread.java:856)
07-25 03:47:57.666: E/AndroidRuntime(799): Caused by: java.lang.NullPointerException
07-25 03:47:57.666: E/AndroidRuntime(799): at com.theproblemsolver.JSONParsser.getJSONFromURI(JSONParsser.java:35)
07-25 03:47:57.666: E/AndroidRuntime(799): at com.theproblemsolver.asynctask.doInBackground(MainActivity.java:60)
07-25 03:47:57.666: E/AndroidRuntime(799): at com.theproblemsolver.asynctask.doInBackground(MainActivity.java:1)
07-25 03:47:57.666: E/AndroidRuntime(799): at android.os.AsyncTask$2.call(AsyncTask.java:287)
07-25 03:47:57.666: E/AndroidRuntime(799): at java.util.concurrent.FutureTask.run(FutureTask.java:234)
主要活动
public class MainActivity extends Activity {
EditText et;
Button getanswer;
JSONArray ResultsSet = null; {}
@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) {
new asynctask().execute();
}
});
}
}
class asynctask extends AsyncTask<String, Void, JSONObject> {
private static final String TAG_RESULTS = "ResultsSet";
private static final String TAG_SUBJECT = "Subject";
private static final String TAG_NUMANSWERS = "NumAnswers";
private static final String TAG_QUESTION = "Question";
private static final String TAG_QUESTION_CONTENT = "Content";
private static final String TAG_QUESTION_CHOSENANSWER = "ChosenAnswer";
private static final String TAG_QUESTION_ANSWERS = "Answers";
public JSONArray json;
@Override
protected JSONObject doInBackground(String... params) {
JSONParsser jParser = new JSONParsser();
String uRI = null;
JSONObject json = jParser.getJSONFromURI(uRI);
return json ;
}{ }
@Override
protected void onPostExecute(JSONObject json) {
JSONArray ResultsSet = null; {
try {
ResultsSet = json.getJSONArray(TAG_RESULTS);
} catch (JSONException e) {
e.printStackTrace();
}
return;
}}}
JSONParser Class
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://answers.yahooapis.com/AnswerService/V1/questionSearch?appid=vcE15nV34EYK7oAge17Ws6nF3DOzc5ccb4PsWtQjW2YTG3gjKbz8exOHYQr6Psizg&query=" + et.getText() + "sort&type=resolved&results&output=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{}
}{
}}
InstanceofJSONParser Class
public class JSONParserInstance {
JSONParsser jParser = new JSONParsser();
public String uRI;
JSONObject json = jParser.getJSONFromURI(uRI);
private static final String TAG_RESULTS = "ResultsSet";
private static final String TAG_SUBJECT = "Subject";
private static final String TAG_NUMANSWERS = "NumAnswers";
private static final String TAG_QUESTION = "Question";
private static final String TAG_QUESTION_CONTENT = "Content";
private static final String TAG_QUESTION_CHOSENANSWER = "ChosenAnswer";
private static final String TAG_QUESTION_ANSWERS = "Answers";
JSONArray ResultsSet = null; {
try {
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 NmAnswers = 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);
}
} catch (JSONException e) {
e.printStackTrace();
}}}
答案 0 :(得分：2)
String uRI = null;
JSONObject json = jParser.getJSONFromURI(uRI);
您正在尝试解析null-String并且您正在获取java.lang.NullPointerException
尝试new asynctask().execute(someUrl);代替new asynctask().execute();并在doInBackground方法中将String uRI = null;更改为String uRI = params[0]。
答案 1 :(得分：0)
在您的代码中，您将null值传递给getJSONFromURI()，这会导致空指针异常
String uRI = null;
JSONObject json = jParser.getJSONFromURI(uRI); // Passing null
答案 2 :(得分：0)
更改
@Override
protected JSONObject doInBackground(String... params) {
JSONParsser jParser = new JSONParsser();
String uRI = null;
JSONObject json = jParser.getJSONFromURI(uRI);
return json ;
}{ }
到
String uRI = null;//don't make it null
@Override
protected JSONObject doInBackground(String... params) {
JSONParsser jParser = new JSONParsser();
JSONObject json = jParser.getJSONFromURI(uRI);
return json ;
}