您好，我在使用 asyncTask 填充惰性 ListView 时遇到问题。所以我在寻求你的帮助。
这是我的活动课程：
import java.util.ArrayList;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ListView;
import com.outsoucefarm.musicagratis.functions.AlbumLazyAdapter;
import com.outsoucefarm.musicagratis.functions.JSONParser;
import com.outsoucefarm.musicagratis.objects.Albums;
import com.outsoucefarm.musicagratis.objects.Songs;
import com.outsourcefarm.musicagratis.R;
public class LatestAlbums extends Activity {
// widgets
private ListView list;
private ImageView back;
private EditText find;
// URL to make request
private static String url = "http://someurl.com/data.json";
// JSON Node names
private static final String TAG_ALBUMS = "albums";
private static final String TAG_ID = "id";
private static final String TAG_NAME = "name";
private static final String TAG_SINGER = "singer";
private static final String TAG_GENRE = "genre";
private static final String TAG_MIX = "mix";
private static final String TAG_THUMB = "thumb";
private static final String TAG_SONGS = "songs";
private static final String TAG_SONG_TITLE = "song";
private static final String TAG_SONG_ARTIST = "artist";
private static final String TAG_SONG_MP3 = "mp3";
private static final String TAG_SONG_MP4 = "mp4";
private static final String TAG_SONG_THUMB = "thumb";
// albums JSONArray
private JSONArray albums = null;
private JSONArray sngs = null;
private ArrayList<Albums> albumsArray;
private ArrayList<Songs> songsArray;
private AlbumLazyAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.latest_albums);
try {
loadJSON();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// initWidgets();
}
private void initWidgets() {
list = (ListView) findViewById(R.id.listView1);
back = (ImageView) findViewById(R.id.latest_back_img);
find = (EditText) findViewById(R.id.latest_search_et);
back.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
finish();
}
});
adapter = new AlbumLazyAdapter(this, albumsArray);
list.setAdapter(adapter);
}
public void loadJSON() throws JSONException {
AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {
@Override
protected Void doInBackground(Void... params) {
// Creating JSON Parser instance
JSONParser jParser = new JSONParser();
// getting JSON string from URL
JSONObject json = jParser.getJSONFromUrl(url);
JSONObject theJSON;
try {
// Getting Array of albums
theJSON = json.getJSONObject("json");
albums = theJSON.getJSONArray(TAG_ALBUMS);
// sngs=theJSON.getJSONArray(TAG_SONGS);
// looping through All albums
for (int i = 0; i < albums.length(); i++) {
JSONObject c = albums.getJSONObject(i);
// Storing each json item in variable
String album_id = c.getString(TAG_ID);
String album_name = c.getString(TAG_NAME);
String album_singer = c.getString(TAG_SINGER);
String album_mix = c.getString(TAG_MIX);
String album_genre = c.getString(TAG_GENRE);
String album_thumb = c.getString(TAG_THUMB);
albumsArray.add(new Albums(album_id, album_name,
album_singer, album_genre, album_mix,
album_thumb));
Log.v("--", "Albums" + " " + album_id + " "
+ album_name + " " + album_genre + " "
+ album_singer + " " + album_thumb + " "
+ album_mix);
sngs = c.getJSONArray(TAG_SONGS);
// getting songs for the album
for (int j = 0; j < sngs.length(); j++) {
JSONObject songs = sngs.getJSONObject(j);
String song_artist = songs
.getString(TAG_SONG_ARTIST);
String song_mp3 = songs.getString(TAG_SONG_MP3);
String song_mp4 = songs.getString(TAG_SONG_MP4);
String song_thumb = songs.getString(TAG_SONG_THUMB);
String song_title = songs.getString(TAG_SONG_TITLE);
Log.v("--", "Songs: " + j + " " + song_artist + " "
+ song_mp3 + " " + song_mp4 + " "
+ song_thumb + " " + song_title);
songsArray.add(new Songs(song_title, song_artist,
song_mp3, song_mp4, song_thumb));
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
initWidgets();
adapter.notifyDataSetChanged();
}
}; task.execute();
}
}
这是我从 logCat 中得到的：
03-30 19:44:48.352: E/AndroidRuntime(2474): FATAL EXCEPTION: AsyncTask #1
03-30 19:44:48.352: E/AndroidRuntime(2474): java.lang.RuntimeException: An error occured while executing doInBackground()
03-30 19:44:48.352: E/AndroidRuntime(2474): at android.os.AsyncTask$3.done(AsyncTask.java:278)
03-30 19:44:48.352: E/AndroidRuntime(2474): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
03-30 19:44:48.352: E/AndroidRuntime(2474): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
03-30 19:44:48.352: E/AndroidRuntime(2474): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
03-30 19:44:48.352: E/AndroidRuntime(2474): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
03-30 19:44:48.352: E/AndroidRuntime(2474): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
03-30 19:44:48.352: E/AndroidRuntime(2474): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
03-30 19:44:48.352: E/AndroidRuntime(2474): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
03-30 19:44:48.352: E/AndroidRuntime(2474): at java.lang.Thread.run(Thread.java:856)
03-30 19:44:48.352: E/AndroidRuntime(2474): Caused by: java.lang.NullPointerException
03-30 19:44:48.352: E/AndroidRuntime(2474): at com.outsourcefarm.musicagratis.activities.LatestAlbums$2.doInBackground(LatestAlbums.java:116)
03-30 19:44:48.352: E/AndroidRuntime(2474): at com.outsourcefarm.musicagratis.activities.LatestAlbums$2.doInBackground(LatestAlbums.java:1)
03-30 19:44:48.352: E/AndroidRuntime(2474): at android.os.AsyncTask$2.call(AsyncTask.java:264)
03-30 19:44:48.352: E/AndroidRuntime(2474): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
03-30 19:44:48.352: E/AndroidRuntime(2474): ... 5 more
这是在第 116 行：
albumsArray.add(new Albums(album_id, album_name,
album_singer, album_genre, album_mix,
album_thumb));