package com.example.admin.sunshine.app;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
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.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.net.Uri;
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 java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Date;
import java.util.List;
/**
* Created by admin on 12/02/2016.
*/
public class ForecastFragment extends Fragment {
private ArrayAdapter<String> mForecastAdapter;
public ForecastFragment() {
}
@Override
public void onCreate(Bundle saveInstanceState)
{
super.onCreate(saveInstanceState);
setHasOptionsMenu(true);
}
@Override
public void onCreateOptionsMenu(Menu menu,MenuInflater inflater)
{
inflater.inflate(R.menu.forecastfragment,menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item)
{
int id=item.getItemId();
if(id==R.id.action_refresh)
{
FetchWeatherTask weatherTask=new FetchWeatherTask();
weatherTask.execute("London ");
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);
String[] forecastArray={
"Today - Sunny - 88/63",
"Tomorrow - Cloudy - 72/63",
"Wens - Sunny - 88/63",
};
List<String> weekForecast = new ArrayList<String>(Arrays.asList(forecastArray));
ArrayAdapter<String> mForecastAdapter = new ArrayAdapter<String>(getActivity(), R.layout.list_item_forecast, R.id.list_item_forecast_textview, weekForecast);
ListView listView = (ListView)rootView.findViewById(R.id.listview_forecast);
listView.setAdapter(mForecastAdapter);
//listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
// @Override
// public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
// String forecast=mForecastAdapter.getItem(position);
// Intent intent=new Intent(getActivity(),DetailActivity.class).putExtra(Intent.EXTRA_TEXT,forecast);
// startActivity(intent);
// }
// });
return rootView;
}
private class FetchWeatherTask extends AsyncTask<String, Void, String[]> {
private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();
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.
Date date = new Date(time * 1000);
SimpleDateFormat format = new SimpleDateFormat("E, MMM d");
return format.format(date).toString();
}
/**
* Prepare the weather high/lows for presentation.
*/
private String formatHighLows(double high, double low) {
// For presentation, assume the user doesn'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 the JSON string and converts it
* into an Object hierarchy 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_DATETIME = "dt";
final String OWM_DESCRIPTION = "main";
JSONObject forecastJson = new JSONObject(forecastJsonStr);
JSONArray weatherArray = forecastJson.getJSONArray(OWM_LIST);
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 a long. We need to convert that
// into something human-readable, since most people won't read "1400356800" as
// "this saturday".
long dateTime = dayForecast.getLong(OWM_DATETIME);
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 + " - " + description + " - " + highAndLow;
}
for(String s: resultStrs){
Log.v(LOG_TAG, "Forecast entry: " + s);
}
return resultStrs;
}
@Override
protected String[] doInBackground(String... params) {
if(params.length==0){
return null;
}
// 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=7;
String parID="44db6a862fba0b067b1930da0d769e98";
try {
// Construct the URL for the OpenWeatherMap query
// Possible parameters are avaiable 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/daily?";
final String QUERY_PARAM="q";
final String FORMAT_PARAM="mode";
final String UNITS_PARAM="units";
final String DAYS_PARAM="cnt";
final String ID_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(ID_PARAM, parID)
.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.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 it's JSON, adding a newline isn't necessary (it won't affect parsing)
// But it does make debugging a *lot* easier if you print out the completed
// 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 successfully get the weather data, there's no point in attemping
// 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();
}
return null; }
@Override
protected void onPostExecute(String[] result){
if(result !=null)
{
mForecastAdapter.clear();
}
for(String dayForecastStr:result){
mForecastAdapter.add(dayForecastStr);
}
}
}
}
logcat的
02-16 10:44:03.159 2539-2539/com.example.admin.sunshine.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.admin.sunshine.app, PID: 2539
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ArrayAdapter.clear()' on a null object reference
at com.example.admin.sunshine.app.ForecastFragment$FetchWeatherTask.onPostExecute(ForecastFragment.java:272)
at com.example.admin.sunshine.app.ForecastFragment$FetchWeatherTask.onPostExecute(ForecastFragment.java:97)
at android.os.AsyncTask.finish(AsyncTask.java:632)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
答案 0 :(得分：0)
在onCreateView()方法中，您创建了一个局部变量mForecastAdapter，而不是使用片段的mForecastAdapter。因此mForecastAdapter方法中onPostExecute()的片段仍然为空。
答案 1 :(得分：0)
在调用方法
之前检查并处理空指针@Override
protected void onPostExecute(String[] result){
if(result !=null)
{
if(mForecastAdapter!=null){
mForecastAdapter.clear();
}
}
for(String dayForecastStr:result){
if(mForecastAdapter!=null){
mForecastAdapter.add(dayForecastStr);
}
}
}