我正在开发一个Android应用程序，我无法理解为什么我继续在这个类中获取空指针异常。我有一个listview和一个基础适配器，我认为我的代码是正确的，但显然不是。我需要帮助解决这个问题，并将非常感谢所提供的帮助。下面是logcat错误和java代码。
10-20 00:17:39.342: E/AndroidRuntime(24078): FATAL EXCEPTION: AsyncTask #1
10-20 00:17:39.342: E/AndroidRuntime(24078): java.lang.RuntimeException: An error occured while executing doInBackground()
10-20 00:17:39.342: E/AndroidRuntime(24078): at android.os.AsyncTask$3.done(AsyncTask.java:299)
10-20 00:17:39.342: E/AndroidRuntime(24078): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
10-20 00:17:39.342: E/AndroidRuntime(24078): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
10-20 00:17:39.342: E/AndroidRuntime(24078): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
10-20 00:17:39.342: E/AndroidRuntime(24078): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
10-20 00:17:39.342: E/AndroidRuntime(24078): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
10-20 00:17:39.342: E/AndroidRuntime(24078): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
10-20 00:17:39.342: E/AndroidRuntime(24078): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
10-20 00:17:39.342: E/AndroidRuntime(24078): at java.lang.Thread.run(Thread.java:864)
10-20 00:17:39.342: E/AndroidRuntime(24078): Caused by: java.lang.NullPointerException
10-20 00:17:39.342: E/AndroidRuntime(24078): at **com.creation.joopn.VListActivity$LoadVenues.doInBackground(VListActivity.java:150)
10-20 00:17:39.342: E/AndroidRuntime(24078): at com.creation.joopn.VListActivity$LoadVenues.doInBackground(VListActivity.java:1)**
10-20 00:17:39.342: E/AndroidRuntime(24078): at android.os.AsyncTask$2.call(AsyncTask.java:287)
10-20 00:17:39.342: E/AndroidRuntime(24078): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
类
public class VListActivity extends Activity {
TextView name;
String my_id, my_type;
ListView list;
VListAdapter adapter;
// Progress Dialog
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> venueList;
// url to get all products list
private static String Venue_URL = "http://www.createinv.com/list/myVenues.php";
// JSON Node names
static final String TAG_SUCCESS = "success";
static final String KEY_VENUES = "venues";
static final String KEY_ID = "venue_id";
static final String KEY_NAME = "venue_name";
static final String KEY_ADDRESS = "street";
static final String KEY_CITY = "city";
static final String KEY_STATE = "state";
static final String KEY_ZIP = "zip";
static final String KEY_NUMBER = "phone_number";
static final String KEY_BIO = "bio";
JSONArray venues = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
SharedPreferences sp =
PreferenceManager.getDefaultSharedPreferences(this);
my_id = sp.getString("my_id", null);
my_type = sp.getString("my_type", null);
new LoadVenues().execute();
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// if result code 100
if (resultCode == 100) {
Intent intent = getIntent();
finish();
startActivity(intent);
}
}
class LoadVenues extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(VListActivity.this);
pDialog.setMessage("Loading Venues. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("my_id", my_id));
params.add(new BasicNameValuePair("my_type", my_type));
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(Venue_URL, "POST", params);
// Check your log cat for JSON reponse
Log.d("Venues: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of venues
venues = json.getJSONArray(KEY_VENUES);
// looping through All venues
venueList = new ArrayList<HashMap<String, String>>();
for (int i = 0; i < venues.length(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
JSONObject c = venues.getJSONObject(i);
// adding each child node to HashMap key => value
map.put(KEY_ID, c.getString(KEY_ID));
map.put(KEY_NAME, c.getString(KEY_NAME));
map.put(KEY_ADDRESS, c.getString(KEY_ADDRESS));
map.put(KEY_CITY, c.getString(KEY_CITY).concat(", "));
map.put(KEY_STATE, c.getString(KEY_STATE));
map.put(KEY_ZIP, c.getString(KEY_ZIP));
map.put(KEY_NUMBER, c.getString(KEY_NUMBER));
// adding HashList to ArrayList
venueList.add(map);
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data into ListView
* */
adapter = new VListAdapter(VListActivity.this, venueList);
list = (ListView)findViewById(R.id.list);
list.setAdapter(adapter);
}
});
}
}
public class VListAdapter extends BaseAdapter {
private LayoutInflater inflater;
private Context context;
public VListAdapter(Context context, ArrayList<HashMap<String,String>> venueList){
inflater = LayoutInflater.from(context);
this.context = context;
}
public int getCount() {
return venueList.size();
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
View vi=convertView;
if(convertView==null)
vi = inflater.inflate(R.layout.activity_homelist, null);
TextView venue_id = (TextView)vi.findViewById(R.id.venue_id);
TextView name = (TextView)vi.findViewById(R.id.name);
TextView address = (TextView)vi.findViewById(R.id.address1);
TextView city = (TextView)vi.findViewById(R.id.city);
TextView state = (TextView)vi.findViewById(R.id.state);
TextView zip = (TextView)vi.findViewById(R.id.zip);
TextView number = (TextView)vi.findViewById(R.id.phnumber);
HashMap<String, String> vlist = new HashMap<String, String>();
vlist = venueList.get(position);
// Setting all values in listview
venue_id.setText(vlist.get(VListActivity.KEY_ID));
name.setText(vlist.get(VListActivity.KEY_NAME));
name.setOnClickListener(new myOnClickListener(position));
address.setText(vlist.get(VListActivity.KEY_ADDRESS));
city.setText(vlist.get(VListActivity.KEY_CITY));
state.setText(vlist.get(VListActivity.KEY_STATE));
zip.setText(vlist.get(VListActivity.KEY_ZIP));
number.setText(vlist.get(VListActivity.KEY_NUMBER));
return vi;
}
public class myOnClickListener implements OnClickListener{
private int position;
public myOnClickListener(int position){
this.position=position;
}
@Override
public void onClick(View v) {
HashMap<String, String> update = new HashMap<String, String>();
update = venueList.get(position);
Log.d("Testing Click", update.get(VListActivity.KEY_ID));
SharedPreferences sp = PreferenceManager
.getDefaultSharedPreferences(VListActivity.this);
SharedPreferences.Editor edit = sp.edit();
edit.putString("venue_id", update.get(VListActivity.KEY_ID));
edit.commit();
Intent in = new Intent(VListActivity.this, VenueProfileActivity.class);
startActivity(in);
}
}
}
答案 0 :(得分：1)
将ListView文件中的layout更改为
<ListView android:id="@+id/list" <!-- change the id like this -->
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:divider="#dddddd"
android:dividerHeight="1dp" > </ListView>
如果你扩展ListActivity，那么你拥有它的方式会有效，但由于你只是在扩展Activity，所以你不需要以这种方式声明id。你只需给它自己的id。
最初的问题似乎是需要使用“Project - ＆gt; Clean ...”清理项目，然后再次运行项目，因为NPE对给定的代码没有意义。另外，runOnUiThread不需要onPostExecute()，因为该方法已在UI Thread上运行，因此不应在{{1}}中使用。