所以这是我正在处理的代码：
public class MainActivity extends ListActivity {
// url to make request
private static String url = "http://alyssayango.x10.mx/";
private static final String TAG_TYPE = "movie_type";
private static final String TAG_NAME = "movie_name";
private static final String TAG_LENGTH = "movie_length";
private static final String TAG_SCHEDULES = "movie_schedules";
private static final String TAG_CINEMA = "movie_cinema_number";
private static final String TAG_URL = "movie_image_url";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MyTask task = new MyTask(MainActivity.this);
task.execute(url);
}
public String readMovieSchedules(String url) {
StringBuilder builder = new StringBuilder();
HttpClient client = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url);
try {
HttpResponse response = client.execute(httpGet);
StatusLine statusLine = response.getStatusLine();
int statusCode = statusLine.getStatusCode();
if (statusCode == 200) {
HttpEntity entity = response.getEntity();
InputStream content = entity.getContent();
BufferedReader reader = new BufferedReader(new InputStreamReader(content));
String line;
while ((line = reader.readLine()) != null) {
builder.append(line);
}
} else {
Log.e(MainActivity.class.toString(), "Failed to download file");
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return builder.toString();
}
private class MyTask extends AsyncTask<String, Void, String>{
private ProgressDialog pd;
public MainActivity activity;
public MyTask(MainActivity a)
{
activity = a;
}
@Override
protected String doInBackground(String... urls) {
String stringtoparse=null;
for (String url : urls) {
stringtoparse = readMovieSchedules(url); // getting XML from URL
}
return stringtoparse;
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
pd = new ProgressDialog(MainActivity.this);
pd.setTitle("Downloading...");
pd.setMessage("Please wait.");
pd.setCancelable(false);
pd.setIndeterminate(true);
pd.show();
super.onPreExecute();
}
@Override
protected void onPostExecute(String readMovieSchedules) {
// Hashmap for ListView
ArrayList<HashMap<String, String>> movieList = new ArrayList<HashMap<String, String>>();
JSONArray jsonArray;
try {
jsonArray = new JSONArray(readMovieSchedules);
Log.i(MainActivity.class.getName(),
"Number of entries " + jsonArray.length());
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject jsonObject = jsonArray.getJSONObject(i);
Log.i(MainActivity.class.getName(), jsonObject.getString("movie_name"));
// Storing each json item in variable
String name = jsonObject.getString(TAG_NAME);
String type = jsonObject.getString(TAG_TYPE);
String length = jsonObject.getString(TAG_LENGTH);
String cinema = jsonObject.getString(TAG_CINEMA);
String schedules = jsonObject.getString(TAG_SCHEDULES);
String url = jsonObject.getString(TAG_URL);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_NAME, name);
map.put(TAG_TYPE, type);
map.put(TAG_LENGTH, length);
map.put(TAG_CINEMA, cinema);
map.put(TAG_SCHEDULES, schedules);
map.put(TAG_URL, url);
// adding HashList to ArrayList
movieList.add(map);
/**
* Updating parsed JSON data into ListView
* */
THIS IS LINE 178 ListAdapter adapter = new CustomAdapter(MainActivity.this, movieList,
R.layout.list_item,
new String[] { TAG_NAME, TAG_CINEMA, TAG_SCHEDULES, TAG_URL },
new int[] { R.id.name, R.id.cinema, R.id.schedules, R.id.image });
setListAdapter(adapter);
// selecting single ListView item
ListView lv = getListView();
// Launching new screen on Selecting Single ListItem
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String name = ((TextView) view.findViewById(R.id.name)).getText().toString();
String cost = ((TextView) view.findViewById(R.id.cinema)).getText().toString();
String description = ((TextView) view.findViewById(R.id.schedules)).getText().toString();
String url = ((TextView) view.findViewById(R.id.image_)).getText().toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class);
in.putExtra(TAG_NAME, name);
in.putExtra(TAG_CINEMA, cost);
in.putExtra(TAG_SCHEDULES, description);
in.putExtra(TAG_URL, url);
startActivity(in);
}
});
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
pd.dismiss();
super.onPostExecute(readMovieSchedules);
}
}
private class CustomAdapter extends SimpleAdapter {
public ImageLoader imageLoader;
public LayoutInflater inflater = null;
private Activity activity;
private Context mContext;
private URL url;
private Bitmap bmp;
public CustomAdapter(Context context, List<? extends Map<String, ?>> data,
int resource, String[] from, int[] to) {
super(context, data, resource, from, to);
mContext = context;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
THIS IS LINE 238 imageLoader = new ImageLoader(activity.getApplicationContext());
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = getLayoutInflater().inflate(R.layout.list_item,
null);
}
HashMap<String, Object> data = (HashMap<String, Object>) getItem(position);
TextView name = (TextView) convertView.findViewById(R.id.name);
TextView cinema = (TextView) convertView.findViewById(R.id.cinema);
TextView schedules = (TextView) convertView.findViewById(R.id.schedules);
ImageView image = (ImageView) convertView.findViewById(R.id.image);
String nameString = (String) data.get(TAG_NAME);
String cinemaString = (String) data.get(TAG_CINEMA);
String schedulesString = (String) data.get(TAG_SCHEDULES);
String imageURL = (String) data.get(TAG_URL);
name.setText(nameString);
cinema.setText(cinemaString);
schedules.setText(schedulesString);
try {
URL newURL = new URL(imageURL);
bmp = BitmapFactory.decodeStream(newURL.openConnection().getInputStream());
image.setImageBitmap(bmp);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
imageLoader.DisplayImage(imageURL, (Activity)mContext, image);
return convertView;
}
}
}
我在这些行中遇到错误/ NullPointerException：
ListAdapter adapter = new CustomAdapter(MainActivity.this, movieList,
R.layout.list_item,
new String[] { TAG_NAME, TAG_CINEMA, TAG_SCHEDULES, TAG_URL },
new int[] { R.id.name, R.id.cinema, R.id.schedules, R.id.image });
我在这里缺少的是什么？任何帮助深表感谢。感谢。
更新了日志文件：
07-25 10:39:58.564: E/AndroidRuntime(971): FATAL EXCEPTION: main
07-25 10:39:58.564: E/AndroidRuntime(971): java.lang.NullPointerException
07-25 10:39:58.564: E/AndroidRuntime(971): at com.say.stalucia.MainActivity$CustomAdapter.<init>(MainActivity.java:238)
07-25 10:39:58.564: E/AndroidRuntime(971): at com.say.stalucia.MainActivity$MyTask.onPostExecute(MainActivity.java:178)
07-25 10:39:58.564: E/AndroidRuntime(971): at com.say.stalucia.MainActivity$MyTask.onPostExecute(MainActivity.java:1)
07-25 10:39:58.564: E/AndroidRuntime(971): at android.os.AsyncTask.finish(AsyncTask.java:631)
07-25 10:39:58.564: E/AndroidRuntime(971): at android.os.AsyncTask.access$600(AsyncTask.java:177)
07-25 10:39:58.564: E/AndroidRuntime(971): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
第238行：
imageLoader = new ImageLoader(activity.getApplicationContext());
第178行：
ListAdapter adapter = new CustomAdapter(MainActivity.this, movieList,
答案 0 :(得分：1)
activity在行中为空：
imageLoader = new ImageLoader(activity.getApplicationContext());
因为你没有将它分配给构造函数中的任何内容。
为什么不使用上下文对象？
imageLoader = new ImageLoader(mContext);
答案 1 :(得分：0)
看起来你永远不会在CustomAdapter中初始化“activity”变量。
这可能是您的NPE的来源。
您应该使用MainActivity.this代替。
答案 2 :(得分：0)
我认为您正在获取NullPointerException，因为该URL上的JSON消息已损坏。例如，你的json以方括号开头，json必须以大括号开头。
对于某些示例检查the official page.
答案 3 :(得分：0)
获取inflater时，您还在使用activity。在那里也使用mContext。
inflater = (LayoutInflater)mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader = new ImageLoader(mContext.getApplicationContext());