出于某种原因，我通过双重解析得到了一个nullpointer异常。在进一步调查后，我的JSON对象似乎有些问题，但我不知道问题是什么。我从openweathermap api中提取JSON数据。我scrassfully拉，并将数据打印到log.i，但是当我尝试使用JSONObject访问时，我收到一个错误。请帮忙。
代码：
package com.anuraagy.myweather;
import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.*;
import android.content.*;
import android.os.Build;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.StatusLine;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
public class MyActivity extends Activity {
private String s;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.my, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
private JSONObject myObject,mainObject,nameObject;
private ImageView myImage;
private TextView titleText;
private String hello,weatherName,max_temp,min_temp;
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_my, container, false);
RequestTask task = new RequestTask();
task.execute(new String[]{"http://api.openweathermap.org/data/2.5/weather?q=Ashburn&APPID=970bf0e4978dae293b065f8f2830ba58"});
return rootView;
}
public class RequestTask extends AsyncTask<String, String, String> {
private TextView myView;
private String s;
@Override
protected String doInBackground(String... uri) {
HttpClient httpclient = new DefaultHttpClient();
HttpResponse response;
String responseString = null;
try {
response = httpclient.execute(new HttpGet(uri[0]));
StatusLine statusLine = response.getStatusLine();
if (statusLine.getStatusCode() == HttpStatus.SC_OK) {
ByteArrayOutputStream out = new ByteArrayOutputStream();
response.getEntity().writeTo(out);
out.close();
responseString = out.toString();
} else {
//Closes the connection.
response.getEntity().getContent().close();
throw new IOException(statusLine.getReasonPhrase());
}
} catch (ClientProtocolException e) {
//TODO Handle problems..
} catch (IOException e) {
//TODO Handle problems..
}
Log.i("", responseString);
return responseString;
}
@Override
protected void onPostExecute(String result){
Log.i("","hello");
super.onPostExecute(result);
try {
myObject = new JSONObject(result);
nameObject = myObject.getJSONObject("weather");
weatherName = nameObject.getString("main");
mainObject = myObject.getJSONObject("main");
Log.i("Wather Name",weatherName);
Log.i("mainObject",mainObject.toString());
hello = mainObject.getString("temp");
max_temp = mainObject.getString("temp_max");
min_temp = mainObject.getString("temp_min");
} catch(JSONException jsonException){
}
double f = Double.parseDouble(hello);
double max = Double.parseDouble(max_temp);
double min = Double.parseDouble(min_temp);
double realMax = (max - 273)* 1.8 + 32;
double realMin = (min - 273)* 1.8 + 32;
double realTemp = (max - 273)* 1.8 + 32;
int myMax = (int)realMax;
int myMin = (int)realMin;
int myWeather = (int)realTemp;
titleText = (TextView)getActivity().findViewById(R.id.textView3);
String fe = titleText.getText().toString();
fe.replace("definetly",weatherName);
myView = (TextView)getActivity().findViewById(R.id.textView);
// if()
// {
//
// }
// else
// {
//
// }
myImage = (ImageView)getActivity().findViewById(R.id.imageView);
myImage.setImageResource(R.drawable.clearnight);
String weather = myWeather + "";
myView.setText(weather + (char) 0x00B0 +"F");
// //Do anything with response..
}
}
}
}
错误：
10-16 10:01:26.398 664-664/com.anuraagy.myweather E/Trace﹕ error opening trace file: No such file or directory (2)
10-16 10:01:35.058 664-668/com.anuraagy.myweather D/dalvikvm﹕ GC_CONCURRENT freed 75K, 2% free 11112K/11335K, paused 17ms+3ms, total 312ms
10-16 10:01:35.058 664-664/com.anuraagy.myweather D/dalvikvm﹕ WAIT_FOR_CONCURRENT_GC blocked 282ms
10-16 10:01:35.498 664-664/com.anuraagy.myweather D/gralloc_goldfish﹕ Emulator without GPU emulation detected.
10-16 10:01:38.388 664-680/com.anuraagy.myweather I/﹕ {"coord":{"lon":-77.49,"lat":39.04},"sys":{"type":1,"id":2856,"message":0.0194,"country":"US","sunrise":1413458470,"sunset":1413498574},"weather":[{"id":701,"main":"Mist","description":"mist","icon":"50d"},{"id":721,"main":"Haze","description":"haze","icon":"50d"},{"id":741,"main":"Fog","description":"fog","icon":"50d"}],"base":"cmc stations","main":{"temp":288.03,"pressure":1008,"humidity":100,"temp_min":286.15,"temp_max":290.15},"wind":{"speed":2.86,"deg":261.502},"clouds":{"all":90},"dt":1413468071,"id":4744870,"name":"Ashburn","cod":200}
10-16 10:01:38.398 664-664/com.anuraagy.myweather I/﹕ hello
10-16 10:01:38.438 664-664/com.anuraagy.myweather D/AndroidRuntime﹕ Shutting down VM
10-16 10:01:38.438 664-664/com.anuraagy.myweather W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x40a13300)
10-16 10:01:38.448 664-664/com.anuraagy.myweather E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at java.lang.StringToReal.parseDouble(StringToReal.java:244)
at java.lang.Double.parseDouble(Double.java:295)
at com.anuraagy.myweather.MyActivity$PlaceholderFragment$RequestTask.onPostExecute(MyActivity.java:141)
at com.anuraagy.myweather.MyActivity$PlaceholderFragment$RequestTask.onPostExecute(MyActivity.java:91)
at android.os.AsyncTask.finish(AsyncTask.java:631)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
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)
答案 0 :(得分：3)
小心 - ＆＃34;天气＆＃34;是JSONArray，而不是JSONObject。 NullPointerException可能是由于这个原因。
尝试使用myObject.getJSONArray("weather")，然后从里面遍历JSONObjects。
有关最后一部分的更多信息，请参见此处：Accessing members of items in a JSONArray with Java
答案 1 :(得分：0)
看起来myObject没有名为"temp"的项目，所以：
- 在第133行，您将hello设置为null
- 在第141行，您将null传递给Double.parseDouble()
- 获取您的例外情况，因为课程Double无法消化null
那就是它！
在调试器中检查它，但我几乎可以肯定 - 根据您的堆栈跟踪