我正在尝试从 Android 中的天气 api 解析 Json 数据。但我收到错误。以下是 logcat 错误列表：
10-17 21:22:36.395: E/log_tag(304): Error in http connection java.net.UnknownHostException: api.openweathermap.org
10-17 21:22:36.395: E/log_tag(304): Error converting result java.lang.NullPointerException
10-17 21:22:36.425: E/log_tag(304): Error parsing data org.json.JSONException: End of input at character 0 of
10-17 21:22:36.447: E/AndroidRuntime(304): FATAL EXCEPTION: AsyncTask #1
10-17 21:22:36.447: E/AndroidRuntime(304): java.lang.RuntimeException: An error occured while executing doInBackground()
10-17 21:22:36.447: E/AndroidRuntime(304): at android.os.AsyncTask$3.done(AsyncTask.java:200)
10-17 21:22:36.447: E/AndroidRuntime(304): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
10-17 21:22:36.447: E/AndroidRuntime(304): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
10-17 21:22:36.447: E/AndroidRuntime(304): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
10-17 21:22:36.447: E/AndroidRuntime(304): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
10-17 21:22:36.447: E/AndroidRuntime(304): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
10-17 21:22:36.447: E/AndroidRuntime(304): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
10-17 21:22:36.447: E/AndroidRuntime(304): at java.lang.Thread.run(Thread.java:1096)
10-17 21:22:36.447: E/AndroidRuntime(304): Caused by: java.lang.NullPointerException
10-17 21:22:36.447: E/AndroidRuntime(304): at com.example.work.MainActivity$DownloadJSON.doInBackground(MainActivity.java:63)
10-17 21:22:36.447: E/AndroidRuntime(304): at com.example.work.MainActivity$DownloadJSON.doInBackground(MainActivity.java:1)
10-17 21:22:36.447: E/AndroidRuntime(304): at android.os.AsyncTask$2.call(AsyncTask.java:185)
10-17 21:22:36.447: E/AndroidRuntime(304): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
10-17 21:22:36.447: E/AndroidRuntime(304): ... 4 more
这是我的代码：MainActivity.java：
package com.example.work;
import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
public class MainActivity extends Activity {
// Declare Variables
JSONObject jsonobject;
JSONArray jsonarray;
ListView listview;
ListViewAdapter adapter;
ProgressDialog mProgressDialog;
ArrayList<HashMap<String, String>> arraylist;
static String NAME = "rank";
static String TYPE = "country";
static String FLAG = "flag";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Get the view from listview_main.xml
setContentView(R.layout.activity_main);
// Execute DownloadJSON AsyncTask
new DownloadJSON().execute();
}
// DownloadJSON AsyncTask
private class DownloadJSON extends AsyncTask<Void, Void, Void> {
//@Override
//protected void onPreExecute() {
// super.onPreExecute();
// Create a progressdialog
//mProgressDialog = new ProgressDialog(MainActivity.this);
// Set progressdialog message
//mProgressDialog.setMessage("Loading...");
//mProgressDialog.setIndeterminate(false);
// Show progressdialog
//mProgressDialog.show();
// }
@Override
protected Void doInBackground(Void... params) {
// Create an array
arraylist = new ArrayList<HashMap<String, String>>();
// Retrieve JSON Objects from the given URL address
jsonobject = JSONParser
.getJSONfromURL("http://api.openweathermap.org/data/2.5/weather?id=2172797");
try {
// Locate the array name in JSON
jsonarray = jsonobject.getJSONArray("id");
for (int i = 0; i < jsonarray.length(); i++) {
HashMap<String, String> map = new HashMap<String, String>();
jsonobject = jsonarray.getJSONObject(i);
// Retrive JSON Objects
map.put(MainActivity.NAME, jsonobject.getString("main"));
map.put(MainActivity.TYPE, jsonobject.getString("description"));
//map.put(MainActivity.FLAG, jsonobject.getString("restaurantIMAGE"));
// Set the JSON Objects into the array
arraylist.add(map);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args) {
// Locate the listview in listview_main.xml
listview = (ListView) findViewById(R.id.listview);
// Pass the results into ListViewAdapter.java
adapter = new ListViewAdapter(MainActivity.this, arraylist);
// Set the adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
mProgressDialog.dismiss();
}
}
}
JSONParser.java：
public class JSONParser {
public static JSONObject getJSONfromURL(String url) {
InputStream is = null;
String result = "";
JSONObject jArray = null;
// Download JSON data from URL
try {
HttpClient httpclient = new DefaultHttpClient();
HttpGet httpget = new HttpGet(url);
HttpResponse response = httpclient.execute(httpget);
HttpEntity entity = response.getEntity();
is = entity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection " + e.toString());
}
// Convert response to string
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
is, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
try {
jArray = new JSONObject(result);
} catch (JSONException e) {
Log.e("log_tag", "Error parsing data " + e.toString());
}
return jArray;
}
}
ListViewAdapter.java：
public class ListViewAdapter extends BaseAdapter {
// Declare Variables
Context context;
LayoutInflater inflater;
ArrayList<HashMap<String, String>> data;
//ImageLoader imageLoader;
HashMap<String, String> resultp = new HashMap<String, String>();
public ListViewAdapter(Context context,
ArrayList<HashMap<String, String>> arraylist) {
this.context = context;
data = arraylist;
// imageLoader = new ImageLoader(context);
}
@Override
public int getCount() {
return data.size();
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
public View getView(final int position, View convertView, ViewGroup parent) {
// Declare Variables
TextView main;
TextView description;
//ImageView flag;
inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View itemView = inflater.inflate(R.layout.listview_item, parent, false);
// Get the position
resultp = data.get(position);
// Locate the TextViews in listview_item.xml
main = (TextView) itemView.findViewById(R.id.main);
description = (TextView) itemView.findViewById(R.id.description);
// Locate the ImageView in listview_item.xml
//flag = (ImageView) itemView.findViewById(R.id.flag);
// Capture position and set results to the TextViews
main.setText(resultp.get(MainActivity.NAME));
description.setText(resultp.get(MainActivity.TYPE));
// Capture position and set results to the ImageView
// Passes flag images URL into ImageLoader.class
// imageLoader.DisplayImage(resultp.get(MainActivity.FLAG), flag);
// Capture ListView item click
itemView.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// Get the position
resultp = data.get(position);
Intent intent = new Intent(context, SingleItemView.class);
// Pass all data rank
intent.putExtra("name", resultp.get(MainActivity.NAME));
// Pass all data country
intent.putExtra("type", resultp.get(MainActivity.TYPE));
// Pass all data flag
// intent.putExtra("flag", resultp.get(MainActivity.FLAG));
// Start SingleItemView Class
context.startActivity(intent);
}
});
return itemView;
}
}
SingleItemView.java：
public class SingleItemView {
Intent intent = getIntent();
String id = intent.getStringExtra("name");
String name = intent.getStringExtra("type");
private Intent getIntent() {
// TODO Auto-generated method stub
return null;
}
}
布局中的 listview_item.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/main"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/description"/>
</LinearLayout>
我正在按城市 ID 搜索天气数据。但遇到这些错误。