我有一个扩展片段和调用异步任务类的代码。但我不能设定采用者。我面对错误。我在下面添加片段和错误的代码： 设置适配器时，此错误在此行中：
lv.setAdapter(adapter);
这是一个扩展片段的完整代码：
public class AllProductsActivity extends Fragment {
private RadioGroup radioGroup;
private RadioButton radioSexButton;
private Button btnDisplay;
ListView lv;
private ProgressDialog pDialog;
// Creating JSON Parser object
JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> productsList;
// url to get all products list
private static String url_all_products = "http://192.168.1.108/android_connect/get_all_products.php";
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCTS = "products";
private static final String TAG_PID = "pid";
private static final String TAG_NAME = "name";
// products JSONArray
JSONArray products = null;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.all_products, container, false);
productsList = new ArrayList<HashMap<String, String>>();
LoadAllProducts downloadimage = new LoadAllProducts();
lv = (ListView) rootView.findViewById(R.id.list);
downloadimage.execute();
return rootView;
}
}
/**
* Background Async Task to Load all product by making HTTP Request
* */
class LoadAllProducts extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(getActivity());
pDialog.setMessage("Loading products. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting All products from url
* */
protected String doInBackground(String... args) {
// Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);
// Check your log cat for JSON reponse
Log.d("All Products: ", json.toString());
try {
// Checking for SUCCESS TAG
int success = json.getInt(TAG_SUCCESS);
if (success == 1) {
// products found
// Getting Array of Products
products = json.getJSONArray(TAG_PRODUCTS);
// looping through All Products
for (int i = 0; i < products.length(); i++) {
JSONObject c = products.getJSONObject(i);
// Storing each json item in variable
String id = c.getString(TAG_PID);
String name = c.getString(TAG_NAME);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_PID, id);
map.put(TAG_NAME, name);
// adding HashList to ArrayList
productsList.add(map);
}
} else {
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all products
pDialog.dismiss();
/**
* Updating parsed JSON data into ListView
* */
MainCustomList adapter;
// lv = (ListView) getView().findViewById(R.id.list);
String[] test = new String[] { "1", "2", "3" };
adapter = new MainCustomList(getActivity(), test);
lv.setAdapter(adapter);
// }
// });
}
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
lv = (ListView) view.findViewById(R.id.list);}
}
错误：
11-22 14:14:25.080: D/AndroidRuntime(9863): Shutting down VM
11-22 14:14:25.090: W/dalvikvm(9863): threadid=1: thread exiting with uncaught exception (group=0x41cca8b0)
11-22 14:14:25.090: E/AndroidRuntime(9863): FATAL EXCEPTION: main
11-22 14:14:25.090: E/AndroidRuntime(9863): java.lang.NullPointerException
11-22 14:14:25.090: E/AndroidRuntime(9863): at info.androidhive.tabsswipe.AllProductsActivity$LoadAllProducts.onPostExecute(AllProductsActivity.java:330)
11-22 14:14:25.090: E/AndroidRuntime(9863): at info.androidhive.tabsswipe.AllProductsActivity$LoadAllProducts.onPostExecute(AllProductsActivity.java:1)
11-22 14:14:25.090: E/AndroidRuntime(9863): at android.os.AsyncTask.finish(AsyncTask.java:631)
11-22 14:14:25.090: E/AndroidRuntime(9863): at android.os.AsyncTask.access$600(AsyncTask.java:177)
11-22 14:14:25.090: E/AndroidRuntime(9863): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
11-22 14:14:25.090: E/AndroidRuntime(9863): at android.os.Handler.dispatchMessage(Handler.java:99)
11-22 14:14:25.090: E/AndroidRuntime(9863): at android.os.Looper.loop(Looper.java:213)
11-22 14:14:25.090: E/AndroidRuntime(9863): at android.app.ActivityThread.main(ActivityThread.java:5225)
11-22 14:14:25.090: E/AndroidRuntime(9863): at java.lang.reflect.Method.invokeNative(Native Method)
11-22 14:14:25.090: E/AndroidRuntime(9863): at java.lang.reflect.Method.invoke(Method.java:525)
11-22 14:14:25.090: E/AndroidRuntime(9863): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:741)
11-22 14:14:25.090: E/AndroidRuntime(9863): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
11-22 14:14:25.090: E/AndroidRuntime(9863): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
下面：
lv.setAdapter(adapter);
导致NPE的行，因为lv为null。
ListView的 list位于Fragment而不是Fragment容器Activity
使用Fragment的getView方法代替getActivity从Fragment Layout访问ListView：
lv = (ListView) getView().findViewById(R.id.list);
或更好地使用Fragment的onViewCreated或onCreateView方法来初始化视图：
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
lv = (ListView) view.findViewById(R.id.list);
}