我正在编写构建阳光应用程序的 udacity android 教程，我创建了一个刷新按钮来更新天气信息。单击时它没有更新任何信息，我只是得到一个 JSONException。这是代码：_
对于预测片段：
package com.example.android.sunshine;
import android.net.Uri;
import android.os.AsyncTask;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import android.text.format.Time;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
* A placeholder fragment containing a simple view.
*/
public class ForecastFragment extends Fragment {
private ArrayAdapter<String> mForecastAdapter;
public ForecastFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Add this line in order for this to handle menu events.
setHasOptionsMenu(true);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.forecastfragment, menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The actionbar 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_refresh) {
FetchWeatherTask weatherTask = new FetchWeatherTask();
weatherTask.execute("94043");
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
//Once the root view for the fragment has been created, its time to populate
//the ListView with some dummy data.
//Create some dummy data for the ListView. Here's a sample weekly forecast
//represented as "day, whether, high/low"
String[] forecastArray = {
"Today - Sunny - 88/63",
"Tomorrow - Foggy - 70/40",
"Weds - Cloudy - 72/63",
"Thurs - Asteroids - 75/65",
"Fri - Heavy Rain - 65/56",
"Sat - HELP TRAPPED IN WEATHERSTATION - 60/51",
"Sun - Sunny - 80/68"
};
List<String> weekForecast = new ArrayList<String>(
Arrays.asList(forecastArray));
// Now that we have some dummy forecast data, create an ArrayAdapter.
// The ArrayAdapter will take data from a source (like our dummy forecastarary)
// and use it to populate the ListView it's attached to.
ArrayAdapter mForecastAdapter =
new ArrayAdapter<String>(
// The current context (this fragment's parent activity)
getActivity(),
// ID of list item layout
R.layout.list_item_forecast,
// ID of the textview to populate
R.id.list_item_forecast_textview,
// Forecast data
weekForecast);
// Get a reference to the ListView, and attach this adapter
ListView listView = (ListView) rootView.findViewById(
R.id.listview_forecast);
listView.setAdapter(mForecastAdapter);
return rootView;
}
public class FetchWeatherTask extends AsyncTask<String, Void, String[]> {
private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();
/* The date/time conversion code is going to be moved outside the asynctask later,
* so for convinience we are breaking it out into its own method now.
*/
private String getReadableDateString(long time){
// Because the API returns a unix timestamp (measured in seconds),
// it must be converted to milliseconds in order to be converted to valid date.
SimpleDateFormat shortenedDateFormat = new SimpleDateFormat("EEE MMM dd");
return shortenedDateFormat.format(time);
}
/*
* Prepare the weather high/lows for presentation
*/
private String formatHighLows(double high, double low){
// For presentation, assume the user dosen't care about tenths of a degree
long roundedHigh = Math.round(high);
long roundedLow = Math.round(low);
String highLowStr = roundedHigh + "/" + roundedLow;
return highLowStr;
}
/**
* Take the String representing the complete forecast in JSON Format and
* pull out the data we need to construct the Strings needed for the wireframes
*
* Fortunately parsing is easy: constructor takes JSON string and converts it
* into an Object heirarchy for us.
*/
private String[] getWeatherDataFromJson(String forecastJsonStr, int numDays)
throws JSONException {
// These are the names of the JSON objects that need to be extracted
final String OWM_LIST = "list";
final String OWM_WEATHER = "weather";
final String OWM_TEMPERATURE = "temp";
final String OWM_MAX = "max";
final String OWM_MIN = "min";
final String OWM_DESCRIPTION = "main";
JSONObject forecastJson = new JSONObject(forecastJsonStr);
JSONArray weatherArray = forecastJson.getJSONArray(OWM_LIST);
// OWM returns daily forecasts based upon the local time of the city that is being
// asked for, which means that we need to know the GMT offset to translate this data
// properly.
// Since this data is also sent in-order and the first day is always the
// current day, we're going to take advantage of that to get a nice
// normalized UTC date for all of our weather.
Time dayTime = new Time();
dayTime.setToNow();
// we start at the day returned by local time. Otherwise this is a mess.
int julianStartDay = Time.getJulianDay(System.currentTimeMillis(), dayTime.gmtoff);
// now we work exclusively in UTC
dayTime = new Time();
String[] resultStrs = new String[numDays];
for(int i = 0; i<weatherArray.length();i++){
// For now, using the format "Day, description, hi/low"
String day;
String description;
String highAndLow;
// Get the JSON object representing the day
JSONObject dayForecast = weatherArray.getJSONObject(i);
// The date/time is returned as long. We need to convert that
// into someting human-readable, since most people won't read "1400356800" as
// "this saturday"
long dateTime;
// Cheating to convert this to UTC time, which is what we want anyhow
dateTime = dayTime.setJulianDay(julianStartDay+i);
day = getReadableDateString(dateTime);
// description is in a child array called "weather", which is 1 element long.
JSONObject weatherObject = dayForecast.getJSONArray(OWM_WEATHER).getJSONObject(0);
description = weatherObject.getString(OWM_DESCRIPTION);
// Temperatures are in a child object called "temp". Try not to name variables
// "temp" when working with temperature. It confuses everybody.
JSONObject temperatureObject = dayForecast.getJSONObject(OWM_TEMPERATURE);
double high = temperatureObject.getDouble(OWM_MAX);
double low = temperatureObject.getDouble(OWM_MIN);
highAndLow = formatHighLows(high, low);
resultStrs[i] = day + "-" + "-" + highAndLow;
}
for (String s : resultStrs){
Log.v(LOG_TAG, "Forecast entry: " + s);
}
return resultStrs;
}
@Override
protected String[] doInBackground(String... params) {
// These two need to be declared outside the try/catch
// so that they can be closed in the finally block.
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
// Will contain the raw JSON response as a string
String forecastJsonStr = null;
String format = "json";
String units = "metric";
int numDays = 5;
try {
// Construct the URL for the OpenWeatherMap query
// Possible parameters are available at OWM's forecast API page , at
// http:// openweathermap.org/API#forecast
final String FORECAST_BASE_URL =
"http://api.openweathermap.org/data/2.5/forecast?";
final String QUERY_PARAM = "q";
final String FORMAT_PARAM = "mode";
final String UNITS_PARAM = "units";
final String DAYS_PARAM = "cnt";
final String APPID_PARAM = "APPID";
Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon()
.appendQueryParameter(QUERY_PARAM, params[0])
.appendQueryParameter(FORMAT_PARAM, format)
.appendQueryParameter(UNITS_PARAM, units)
.appendQueryParameter(DAYS_PARAM, Integer.toString(numDays))
.appendQueryParameter(APPID_PARAM, BuildConfig.OPEN_WEATHER_MAP_API_KEY)
.build();
URL url = new URL(builtUri.toString());
Log.v(LOG_TAG, "Built URI " + builtUri.toString());
// Create the request to OpenWeatherMap, and open the connection
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.setRequestProperty("User-Agent", "Mozilla/5.0 ( compatible ) ");
urlConnection.setRequestProperty("Accept", "*/*");
urlConnection.setDoOutput(false);
urlConnection.connect();
// Read the input stream into a String
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
// Nothing to do
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
// Since its JSON, adding a new line isn't necessary(it won't affect parsing)
// But it does make debugging a *lot* easier if you want to print out the complecated
// buffer for debugging
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
// Stream was empty. No point in parsing.
return null;
}
forecastJsonStr = buffer.toString();
Log.v(LOG_TAG, "Forecast JSON String: " + forecastJsonStr);
} catch (IOException e) {
Log.e(LOG_TAG, "Error", e);
// If the code didn't succefully get the weather data, there is no point in attempting
// to parse it.
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(LOG_TAG, "Error closing stream", e);
}
}
}
try {
return getWeatherDataFromJson(forecastJsonStr, numDays);
} catch (JSONException e) {
Log.e(LOG_TAG, e.getMessage(), e);
e.printStackTrace();
}
// This will only happen if there was an error getting or parsing the forecast.
return null;
}
@Override
protected void onPostExecute(String[] result){
if (result != null){
mForecastAdapter.clear();
for (String dayForecastStr : result){
mForecastAdapter.add(dayForecastStr);
}
// New data is back from the server. Yep!!!
}
}
}
logcat 错误信息：
08-26 11:37:55.432 2277-3097/com.example.android.sunshine E/FetchWeatherTask: No value for temp
org.json.JSONException: No value for temp
at org.json.JSONObject.get(JSONObject.java:389)
at org.json.JSONObject.getJSONObject(JSONObject.java:609)
at com.example.android.sunshine.ForecastFragment$FetchWeatherTask.getWeatherDataFromJson(ForecastFragment.java:208)
at com.example.android.sunshine.ForecastFragment$FetchWeatherTask.doInBackground(ForecastFragment.java:323)
at com.example.android.sunshine.ForecastFragment$FetchWeatherTask.doInBackground(ForecastFragment.java:119)
at android.os.AsyncTask$2.call(AsyncTask.java:295)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
通过用 openweathermap api 中的真实数据替换虚拟数据，我无法弄清楚它为什么不更新。
我从 api 获得的这个 JSON 字符串：
V/FetchWeatherTask: Forecast JSON String: {"city":{"id":5375480,"name":"Mountain View","coord":{"lon":-122.083847,"lat":37.386051},"country":"US","population":0,"sys":{"population":0}},"cod":"200","message":0.0383,"cnt":5,"list":[{"dt":1472418000,"main":{"temp":25.84,"temp_min":24.15,"temp_max":25.84,"pressure":993.56,"sea_level":1031.58,"grnd_level":993.56,"humidity":71,"temp_kf":1.69},"weather":[{"id":800,"main":"Clear","description":"clear sky","icon":"01d"}],"clouds":{"all":0},"wind":{"speed":1.42,"deg":253},"rain":{},"sys":{"pod":"d"},"dt_txt":"2016-08-28 21:00:00"},{"dt":1472428800,"main":{"temp":25.84,"temp_min":24.57,"temp_max":25.84,"pressure":992.76,"sea_level":1030.67,"grnd_level":992.76,"humidity":68,"temp_kf":1.27},"weather":[{"id":800,"main":"Clear","description":"clear sky","icon":"01n"}],"clouds":{"all":0},"wind":{"speed":1.4,"deg":260.004},"rain":{},"sys":{"pod":"n"},"dt_txt":"2016-08-29 00:00:00"},{"dt":1472439600,"main":{"temp":19.81,"temp_min":18.97,"temp_max":19.81,"pressure":992.9,"sea_level":1030.9,"grnd_level":992.9,"humidity":79,"temp_kf":0.85},"weather":[{"id":800,"main":"Clear","description":"clear sky","icon":"01n"}],"clouds":{"all":0},"wind":{"speed":1.2,"deg":264.002},"rain":{},"sys":{"pod":"n"},"dt_txt":"2016-08-29 03:00:00"},{"dt":1472450400,"main":{"temp":14.24,"temp_min":13.82,"temp_max":14.24,"pressure":993.56,"sea_level":1031.77,"grnd_level":993.56,"humidity":92,"temp_kf":0.42},"weather":[{"id":800,"main":"Clear","description":"clear sky","icon":"01n"}],"clouds":{"all":0},"wind":{"speed":1.48,"deg":291.5},"rain":{},"sys":{"pod":"n"},"dt_txt":"2016-08-29 06:00:00"},{"dt":1472461200,"main":{"temp":11.13,"temp_min":11.13,"temp_max":11.13,"pressure":993.2,"sea_level":1031.64,"grnd_level":993.2,"humidity":98,"temp_kf":0},"weather":[{"id":800,"main":"Clear","description":"clear sky","icon":"02n"}],"clouds":{"all":8},"wind":{"speed":1.06,"deg":298.504},"rain":{},"sys":{"pod":"n"},"dt_txt":"2016-08-29 09:00:00"}]}