我试图在Android片段中创建一个JSON填充的列表视图。应用程序在AsyncTask区域崩溃，但我不确定问题是什么。我试图通过使用活动的原始教程，但我将其转换为片段：http://www.mybringback.com/tutorial-series/13239/android-mysql-php-json-part-6-json-parsing-and-android-design/;如果需要，很乐意发布整个片段代码。如果您需要更多信息，请与我们联系。
片段整体：
public class mainViewController extends ListFragment
{
Context context;
// Progress Dialog
private ProgressDialog pDialog;
// testing on Emulator:
private static final String READ_COMMENTS_URL = "https://MY_URL";
// JSON IDS:
@SuppressWarnings("unused")
private static final String TAG_SUCCESS = "success";
private static final String TAG_TITLE = "title";
private static final String TAG_POSTS = "posts";
@SuppressWarnings("unused")
private static final String TAG_POST_ID = "post_id";
private static final String TAG_USERNAME = "username";
private static final String TAG_MESSAGE = "message";
// it's important to note that the message is both in the parent branch of
// our JSON tree that displays a "Post Available" or a "No Post Available"
// message,
// and there is also a message for each individual post, listed under the
// "posts"
// category, that displays what the user typed as their message.
// An array of all of our comments
private JSONArray mComments = null;
// manages all of our comments in a list.
private ArrayList<HashMap<String, String>> mCommentList;
public mainViewController()
{
}
String[] mainFeed = {};
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// // TODO Auto-generated method stub
// ArrayAdapter<String> adapter = new ArrayAdapter<String>(
// inflater.getContext(), android.R.layout.simple_list_item_1,
// mainFeed);
//
// setListAdapter(adapter);
return super.onCreateView(inflater, container, savedInstanceState);
}
@Override
public void onResume() {
// TODO Auto-generated method stub
super.onResume();
// loading the comments via AsyncTask
new LoadComments().execute();
}
public void addComment(View v) {
// Intent i = new Intent(ReadComments.this, AddComment.class);
// startActivity(i);
}
/**
* Retrieves recent post data from the server.
*/
public void updateJSONdata() {
// Instantiate the arraylist to contain all the JSON data.
// we are going to use a bunch of key-value pairs, referring
// to the json element name, and the content, for example,
// message it the tag, and "I'm awesome" as the content..
mCommentList = new ArrayList<HashMap<String, String>>();
// Bro, it's time to power up the J parser
JSONParser jParser = new JSONParser();
// Feed the beast our comments url, and it spits us
// back a JSON object. Boo-yeah Jerome.
JSONObject json = jParser.getJSONFromUrl(READ_COMMENTS_URL);
// when parsing JSON stuff, we should probably
// try to catch any exceptions:
try {
// I know I said we would check if "Posts were Avail." (success==1)
// before we tried to read the individual posts, but I lied...
// mComments will tell us how many "posts" or comments are
// available
mComments = json.getJSONArray(TAG_POSTS);
// looping through all posts according to the json object returned
for (int i = 0; i < mComments.length(); i++) {
JSONObject c = mComments.getJSONObject(i);
// gets the content of each tag
String title = c.getString(TAG_TITLE);
String content = c.getString(TAG_MESSAGE);
String username = c.getString(TAG_USERNAME);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_TITLE, title);
map.put(TAG_MESSAGE, content);
map.put(TAG_USERNAME, username);
// adding HashList to ArrayList
mCommentList.add(map);
// annndddd, our JSON data is up to date same with our array
// list
}
} catch (JSONException e) {
e.printStackTrace();
}
}
/**
* Inserts the parsed data into the listview.
*/
private void updateList() {
// For a ListActivity we need to set the List Adapter, and in order to do
//that, we need to create a ListAdapter. This SimpleAdapter,
//will utilize our updated Hashmapped ArrayList,
//use our single_post xml template for each item in our list,
//and place the appropriate info from the list to the
//correct GUI id. Order is important here.
ListAdapter adapter = new SimpleAdapter(this.context, mCommentList,
R.layout.single_post, new String[] { TAG_TITLE, TAG_MESSAGE,
TAG_USERNAME }, new int[] { R.id.title, R.id.message,
R.id.username });
// I shouldn't have to comment on this one:
setListAdapter(adapter);
// Optional: when the user clicks a list item we
//could do something. However, we will choose
//to do nothing...
ListView lv = getListView();
lv.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// This method is triggered if an item is click within our
// list. For our example we won't be using this, but
// it is useful to know in real life applications.
}
});
}
public class LoadComments extends AsyncTask<Void, Void, Boolean> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// pDialog = new ProgressDialog(mainViewController.this);
// pDialog.setMessage("Loading Posts...");
// pDialog.setIndeterminate(false);
// pDialog.setCancelable(true);
// pDialog.show();
}
@Override
protected Boolean doInBackground(Void... arg0) {
updateJSONdata();
return null;
}
@Override
protected void onPostExecute(Boolean result) {
super.onPostExecute(result);
//pDialog.dismiss();
updateList();
}
}
@Override
public void onListItemClick(ListView l, View v, int position, long id)
{
// TODO Auto-generated method stub
super.onListItemClick(l, v, position, id);
}
}
的AsyncTask：
public class LoadComments extends AsyncTask<Void, Void, Boolean> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// pDialog = new ProgressDialog(mainViewController.this);
// pDialog.setMessage("Loading Posts...");
// pDialog.setIndeterminate(false);
// pDialog.setCancelable(true);
// pDialog.show();
}
@Override
protected Boolean doInBackground(Void... arg0) {
updateJSONdata();
return null;
}
@Override
protected void onPostExecute(Boolean result) {
super.onPostExecute(result);
//pDialog.dismiss();
updateList();
}
}
@Override
public void onListItemClick(ListView l, View v, int position, long id)
{
// TODO Auto-generated method stub
super.onListItemClick(l, v, position, id);
}
}
Android错误：
08-04 22：14：53.530：E / AndroidRuntime（22819）：致命异常：主要 08-04 22：14：53.530：E / AndroidRuntime（22819）：处理：com.rynovation.kline，PID：22819 08-04 22：14：53.530：E / AndroidRuntime（22819）：java.lang.NullPointerException 08-04 22：14：53.530：E / AndroidRuntime（22819）：在android.widget.SimpleAdapter。（SimpleAdapter.java:85） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at com.rynovation.kline.mainViewController.updateList（mainViewController.java:159） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at com.rynovation.kline.mainViewController.access $ 0（mainViewController.java:152） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at com.rynovation.kline.mainViewController $ LoadComments.onPostExecute（mainViewController.java:209） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at com.rynovation.kline.mainViewController $ LoadComments.onPostExecute（mainViewController.java:1） 08-04 22：14：53.530：E / AndroidRuntime（22819）：在android.os.AsyncTask.finish（AsyncTask.java:632） 08-04 22：14：53.530：E / AndroidRuntime（22819）：在android.os.AsyncTask.access $ 600（AsyncTask.java:177） 08-04 22：14：53.530：E / AndroidRuntime（22819）：在android.os.AsyncTask $ InternalHandler.handleMessage（AsyncTask.java:645） 08-04 22：14：53.530：E / AndroidRuntime（22819）：在android.os.Handler.dispatchMessage（Handler.java:102） 08-04 22：14：53.530：E / AndroidRuntime（22819）：在android.os.Looper.loop（Looper.java:146） 08-04 22：14：53.530：E / AndroidRuntime（22819）：在android.app.ActivityThread.main（ActivityThread.java:5487） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at java.lang.reflect.Method.invokeNative（Native Method） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at java.lang.reflect.Method.invoke（Method.java:515） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1283） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1099） 08-04 22：14：53.530：E / AndroidRuntime（22819）：at dalvik.system.NativeStart.main（Native Method）