我正在尝试使用AsyncTask从OWM API显示7天天气预报。
doInBackground（String ... param）方法也可以正常工作。我已经检查了LOGCAT。
异步完成执行后。我试图刷新菜单中刷新按钮上的ListView。但是似乎onPostExecute（）确实在乎。
ForecastFragment.java
package com.example.sunshine;
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;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.net.Uri;
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.ArrayAdapter;
import android.widget.ListView;
/**
* A placeholder fragment containing a simple view.
*/
public class ForecastFragment extends Fragment {
private ArrayAdapter<String> mForeCastAdapter;
public String[] forecastArray;
public ForecastFragment() {
}
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.forecastfragment, menu);
}
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_refresh) {
new FetchWeatherTask().execute("44700");
return true;
}
return super.onOptionsItemSelected(item);
}
protected void onPostExecute(String[] result) {
if (result != null) {
Log.v("msg", result[0]);
mForeCastAdapter.clear();
// forecastArray = result;
for (String dayForecastStr : result) {
mForeCastAdapter.add(dayForecastStr);
// mForeCastAdapter.notifyDataSetChanged();
}
}
mForeCastAdapter.notifyDataSetChanged();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
String[] list = { "1", "2", "3" };
List<String> weekForeCast = new ArrayList<String>(
Arrays.asList(list));
mForeCastAdapter = new ArrayAdapter<String>(getActivity(),
R.layout.list_item_forecast, R.id.list_item_forecast_textview,
weekForeCast);
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
ListView weekList = (ListView) rootView
.findViewById(R.id.list_item_forecast);
weekList.setAdapter(mForeCastAdapter);
return rootView;
}
}
class FetchWeatherTask extends AsyncTask<String, Void, String[]> {
private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();
protected ArrayAdapter<String> mForeCastAdapter;
/*
* The date/time conversion code is going to be moved outside the asynctask later, so for convenience we're 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.
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 Array : " + 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 = 7;
try {
// Construct the URL for the OpenWeatherMap query
// Possible parameters are avaiable at OWM's forecast API page, at
// http://openweathermap.org/API#forecast
// URL url = new
// URL("http://api.openweathermap.org/data/2.5/forecast/daily?" +
// "q=94043&mode=json&units=metric&cnt=7");
final String FORECAST_BASE_URL= ="http://api.openweathermap.org/
data/2.5/forecast/daily?";
final String QUERY_PARAM = "q";
final String MODE_PARAM = "mode";
final String UNIT_PARAM = "units";
final String DAYS_PARAM = "cnt";
Uri urlBuild = Uri
.parse(FORECAST_BASE_URL)
.buildUpon()
.appendQueryParameter(QUERY_PARAM, params[0])
.appendQueryParameter(MODE_PARAM, format)
.appendQueryParameter(UNIT_PARAM, units)
.appendQueryParameter(DAYS_PARAM, Integer.toString(numDays))
.build();
URL url = new URL(urlBuild.toString());
//Log.v(LOG_TAG, "Build URL " + urlBuild.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;
}
}
最佳答案
异步任务没有onPostExecute()方法。您的片段中有一个名为onPostExecute()的方法，但asynctask中没有。
请注意，您的IDE不会在那里自动完成@Override。如果您自己在其中添加它，则会收到有关不覆盖基类方法的错误。
关于java - AsyncTask不调用onPostExecute(结果结果)，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/24814422/