Java ArrayAdapter中的Android NullPointerException<；字符串>；由于AsyncTask onPostExecute（）
在使用AsyncTask时，我在android项目上遇到了空指针异常问题。例外情况如下：Java ArrayAdapter中的Android NullPointerException<；字符串>；由于AsyncTask onPostExecute（）,java,android,android-asynctask,nullpointerexception,android-arrayadapter,Java,Android,Android Asynctask,Nullpointerexception,Android Arrayadapter,在使用AsyncTask时，我在android项目上遇到了空指针异常问题。例外情况如下： 03-17 02:17:36.774 14084-14084/me.ashkelon.sunshine W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41934ce0) 03-17 02:17:36.784 14084-14084/me.ashkelon.sunshine E/AndroidRun
03-17 02:17:36.774 14084-14084/me.ashkelon.sunshine W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41934ce0)
03-17 02:17:36.784 14084-14084/me.ashkelon.sunshine E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: me.ashkelon.sunshine, PID: 14084
java.lang.NullPointerException
at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)
at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)
at android.widget.AbsListView.obtainView(AbsListView.java:2255)
at android.widget.ListView.makeAndAddView(ListView.java:1790)
at android.widget.ListView.fillDown(ListView.java:691)
at android.widget.ListView.fillSpecific(ListView.java:1349)
at android.widget.ListView.layoutChildren(ListView.java:1608)
at android.widget.AbsListView.onLayout(AbsListView.java:2087)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:502)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1717)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1571)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1480)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14841)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1986)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1743)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:996)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5603)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
at android.view.Choreographer.doCallbacks(Choreographer.java:574)
at android.view.Choreographer.doFrame(Choreographer.java:544)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5146)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
at dalvik.system.NativeStart.main(Native Method)
03-17 02:22:37.059 14084-14084/me.ashkelon.sunshine I/Process﹕ Sending signal. PID: 14084 SIG: 9
package me.ashkelon.sunshine;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.v4.app.Fragment;
import android.text.format.Time;
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 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.List;
/**
* A placeholder fragment containing a simple view.
*/
public class ForecastFragment extends Fragment {
private ArrayAdapter<String> forecastAdapter;
public ForecastFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//handle menu events (has options)
setHasOptionsMenu(true);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.menu_forecast, menu);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Create some dummy data for the ListView. Here's a sample weekly forecast
String[] data = {
"Mon 6/23 - Sunny - 31/17",
"Tue 6/24 - Foggy - 21/8",
"Wed 6/25 - Cloudy - 22/17",
"Thurs 6/26 - Rainy - 18/11",
"Fri 6/27 - Foggy - 21/10",
"Sat 6/28 - TRAPPED IN WEATHERSTATION - 23/18",
"Sun 6/29 - Sunny - 20/7"
};
List<String> weekForecast = new ArrayList<String>(Arrays.asList(data));
// Now that we have some dummy forecast data, create an ArrayAdapter.
// The ArrayAdapter will take data from a source (like our dummy forecast) and
// use it to populate the ListView it's attached to.
forecastAdapter =
new ArrayAdapter<String>(
getActivity(), // The current context (this activity)
R.layout.list_item_forecast, // The name of the layout ID.
R.id.list_item_forecast_textview, // The ID of the textview to populate.
weekForecast);
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
// Get a reference to the ListView, and attach this adapter to it.
ListView listView = (ListView) rootView.findViewById(R.id.listView_forecast);
listView.setAdapter(forecastAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener(){
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String forecast = forecastAdapter.getItem(position);
Intent intent = new Intent(getActivity(),DetailActivity.class)
.putExtra(Intent.EXTRA_TEXT, forecast);
startActivity(intent);
}
});
return rootView;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if(id==R.id.action_refresh){
FetchWeatherTask fetch = new FetchWeatherTask();
SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(getActivity());
String location = pref.getString(getString(R.string.pref_location_key), getString(R.string.pref_location_default));
fetch.execute(location);
return true;
}
if(id==R.id.action_settings){
Intent intent = new Intent(getActivity(),SettingsActivity.class);
startActivity(intent);
return true;
}
if (id == R.id.action_settings) {
Intent intent = new Intent(getActivity(), SettingsActivity.class);
startActivity(intent);
return true;
}
return super.onOptionsItemSelected(item);
}
//////////////////////////////////////////////////////////////////////////////
/////////////////////////// GET DATA FROM API///////////////////////////////////
//////////////////////////////////////////////////////////////////////////
public class FetchWeatherTask extends AsyncTask<String,Void,String[]> {
private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();
@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 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/daily?";
final String QUERY_PARAM = "q";
final String FORMAT_PARAM = "mode";
final String UNITS_PARAM = "units";
final String DAYS_PARAM = "cnt";
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))
.build();
URL url = new URL(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) {
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();
} catch (IOException e) {
Log.e(LOG_TAG, "Error ", e);
// If the code didn't successfully get the weather data, there's 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();
}
return null;
}
/* 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.
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 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.
*/
////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////////
/////////////////////////// PARSE JSON///////////////////////////////////
//////////////////////////////////////////////////////////////////////////
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 a long. We need to convert that
// into something 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 + " - " + description + " - " + highAndLow;
}
for (String s : resultStrs) {
}
return resultStrs;
}
@Override
protected void onPostExecute(String[] result) {
if(result != null){
Log.v(LOG_TAG, result[0]);
forecastAdapter.clear();
for(String dayForecastStr : result) {
forecastAdapter.add(dayForecastStr);
}
Log.v(LOG_TAG, result[0]);
}
}
}
}
package me.ashkelon.sunshine；
导入android.content.Intent；
导入android.content.SharedReferences；
导入android.net.Uri；
导入android.os.AsyncTask；
导入android.os.Bundle；
导入android.preference.PreferenceManager；
导入android.support.v4.app.Fragment；
导入android.text.format.Time；
导入android.util.Log；
导入android.view.LayoutInflater；
导入android.view.Menu；
导入android.view.MenuInflater；
导入android.view.MenuItem；
导入android.view.view；
导入android.view.ViewGroup；
导入android.widget.AdapterView；
导入android.widget.ArrayAdapter；
导入android.widget.ListView；
导入org.json.JSONArray；
导入org.json.JSONException；
导入org.json.JSONObject；
导入java.io.BufferedReader；
导入java.io.IOException；
导入java.io.InputStream；
导入java.io.InputStreamReader；
导入java.net.HttpURLConnection；
导入java.net.URL；
导入java.text.simpleDataFormat；
导入java.util.ArrayList；
导入java.util.array；
导入java.util.List；
/**
*包含简单视图的占位符片段。
*/
公共类ForecastFragment扩展了片段{
专用阵列适配器forecastAdapter；
公众预报员（）{
}
@凌驾
创建时的公共void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
//处理菜单事件（具有选项）
设置选项菜单（真）；
}
@凌驾
创建选项菜单（菜单菜单，菜单充气机）{
充气机。充气（右菜单。菜单\预测，菜单）；
}
@凌驾
创建视图上的公共视图（布局、充气机、视图组容器、，
Bundle savedInstanceState）{
//为ListView创建一些虚拟数据
字符串[]数据={
“周一6/23 - 阳光明媚-2017年11月31日“，
“6月24日星期二-大雾-21月8日”，
“6月25日星期三-多云-17月22日”，
“6月26日星期四-雨季-11月18日”，
“6月27日星期五-大雾-10月21日”，
“Sat 6/28-被困在气象站-23/18”，
“太阳6/29-晴朗-20/7”
};
List-weekForecast=newarraylist（Arrays.asList（data））；
//现在我们有了一些虚拟预测数据，创建一个ArrayAdapter。
//ArrayAdapter将从源（如我们的虚拟预测）获取数据，然后
//使用它填充它附加到的ListView。
预报器=
新阵列适配器(
getActivity（），//当前上下文（此活动）
R.layout.list\u item\u forecast，//布局ID的名称。
R.id.list\u item\u forecast\u textview，//要填充的textview的id。
周预测）；
视图根视图=充气机。充气（R.layout.fragment_main，容器，错误）；
//获取对ListView的引用，并将此适配器连接到它。
ListView ListView=（ListView）rootView.findViewById（R.id.ListView\u forecast）；
setAdapter（forecasAdapter）；
setOnItemClickListener（新的AdapterView.OnItemClickListener（）{
@凌驾
public void onItemClick（AdapterView父对象、视图、整型位置、长id）{
字符串forecast=ForecasAdapter.getItem（位置）；
意向意向=新意向（getActivity（），DetailActivity.class）
.putExtra（Intent.EXTRA_文本，预测）；
星触觉（意向）；
}
});
返回rootView；
}
@凌驾
公共布尔值onOptionsItemSelected（菜单项项）{
int id=item.getItemId（）；
if（id==R.id.action\u刷新）{
FetchWeatherTask fetch=新建FetchWeatherTask（）；
SharedReferences pref=PreferenceManager.GetDefaultSharedReferences（getActivity（））；
String location=pref.getString（getString（R.String.pref_location_key），getString（R.String.pref_location_default））；
执行（位置）；
返回true；
}
if（id==R.id.action\u设置）{
Intent Intent=new Intent（getActivity（），SettingsActivity.class）；
星触觉（意向）；
返回true；
}
if（id==R.id.action\u设置）{
Intent Intent=new Intent（getActivity（），SettingsActivity.class）；
星触觉（意向）；
返回true；
}
返回super.onOptionsItemSelected（项目）；
}
//////////////////////////////////////////////////////////////////////////////
///////////////////////////从API获取数据///////////////////////////////////
//////////////////////////////////////////////////////////////////////////
公共类FetchWeatherTask扩展了AsyncTask{
私有最终字符串LOG_TAG=FetchWeatherTask.class.getSimpleName（）；
@凌驾
受保护字符串[]doInBackground（字符串…参数）{
//这两个需要在try/catch之外声明
//这样就可以在finally块中关闭它们。
HttpURLConnection-urlConnection=null；
BufferedReader reader=null；
//将以字符串形式包含原始JSON响应。
字符串forecastJsonStr=null；
String format=“json”；
字符串单位=“公制”；
int numDays=7；
试一试{
//构造OpenWeatherMap查询的URL
//可能的参数可在OWM的预测API页面上获得，网址为
// http://openweathermap.org/API#forecast
最终字符串FORECAST_BASE_URL=”http://api.openweathermap.org/data/2.5/forecast/daily?";
protected void onPostExecute(String[] result) {
if(result != null){
List<String> forecastList = new ArrayList<>(Arrays.asList(result));
forecastList.removeAll(Collections.singleton(null));
forecastAdapter.clear();
forecastAdapter.addAll(forecastList);
}
}
// now we work exclusively in UTC
dayTime = new Time();
String[] resultStrs = new String[weatherArray.length()];
for(int i = 0; i < weatherArray.length(); i++) {