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我有一个加载项目列表视图的异步任务。我目前正试图设置onClick来加载一个新的片段与“ID”，是从被点击的列表项中检索。 Android Studio显示我的代码中没有错误。使用asyncTask，接口和片段时出现NullPointerException
当我运行的应用程序，并在列表视图中单击项目我得到这个FC：
02-13 19:49:56.813 20334-20334/com.beerportfolio.beerportfoliopro E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.beerportfolio.beerportfoliopro.ReadJSONResult$1.onItemClick(ReadJSONResult.java:140)
at android.widget.AdapterView.performItemClick(AdapterView.java:298)
at android.widget.AbsListView.performItemClick(AbsListView.java:1237)
at android.widget.ListView.performItemClick(ListView.java:4555)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3037)
at android.widget.AbsListView$1.run(AbsListView.java:3724)
at android.os.Handler.handleCallback(Handler.java:730)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:5789)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:843)
at dalvik.system.NativeStart.main(Native Method)
02-13 19:50:42.112 20864-20870/? E/jdwp﹕ Failed sending reply to debugger: Broken pipe
线140 ReadJSONResult是：
listenerBeer.onArticleSelected(idToSend);
这条线是这个整体的一部分的onClick：
//set up clicks
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
BeerData beerInfo = beerList.get(arg2);
String idToSend = beerInfo.beerId;
//todo: launch beer fragment
listenerBeer.onArticleSelected(idToSend);
}
});
所有ReadJSONResult代码：
public class ReadJSONResult extends AsyncTask<String, Void, String> {
Context c;
private ProgressDialog Dialog;
public ReadJSONResult(Context context)
{
c = context;
Dialog = new ProgressDialog(c);
}
//code for on click
OnArticleSelectedListener listenerBeer;
public interface OnArticleSelectedListener{
public void onArticleSelected(String myString);
}
public void setOnArticleSelectedListener(OnArticleSelectedListener listener){
this.listenerBeer = listener;
}
//end code for onClick
@Override
protected String doInBackground(String... arg0) {
// TODO Auto-generated method stub
return readJSONFeed(arg0[0]);
}
protected void onPreExecute() {
Dialog.setMessage("Searching Beer Cellar");
Dialog.setTitle("Loading");
Dialog.setCancelable(false);
Dialog.show();
}
protected void onPostExecute(String result){
//decode json here
try{
JSONObject json = new JSONObject(result);
//acces listview
ListView lv = (ListView) ((Activity) c).findViewById(android.R.id.list);
//make array list for beer
final List<BeerData> beerList = new ArrayList<BeerData>();
//get json items
for(int i = 0; i < json.getJSONArray("data").length(); i++) {
String beerId = GetBeerDataFromJSON(i,"id", json);
String beerName = GetBeerDataFromJSON(i,"name", json);
String beerDescription = GetBeerDataFromJSON(i,"description" , json);
String beerAbv = GetBeerDataFromJSON(i,"abv" , json);
String beerIbu = GetBeerDataFromJSON(i,"ibu" , json);
String beerIcon = GetBeerIconsFromJSON(i, "icon",json);
String beerMediumIcon = GetBeerIconsFromJSON(i, "medium",json);
String beerLargeIcon = GetBeerIconsFromJSON(i, "large",json);
String beerGlass = GetBeerGlassFromJSON(i, json);
String beerStyle = GetBeerStyleFromJSON(i,"name", json);
String beerStyleDescription = GetBeerStyleFromJSON(i,"description", json);
String beerBreweryId = GetBeerBreweryInfoFromJSON(i, "id", json);
String beerBreweryName = GetBeerBreweryInfoFromJSON(i, "name", json);
String beerBreweryDescription = GetBeerBreweryInfoFromJSON(i, "description", json);
String beerBreweryWebsite = GetBeerBreweryInfoFromJSON(i, "website", json);
//get long and latt
String beerBreweryLat = GetBeerBreweryLocationJSON(i, "longitude", json);
String beerBreweryLong = GetBeerBreweryLocationJSON(i, "latitude", json);
String beerBreweryYear = GetBeerBreweryInfoFromJSON(i, "established", json);
String beerBreweryIcon = GetBeerBreweryIconsFromJSON(i,"large",json);
//create beer object
BeerData thisBeer = new BeerData(beerName, beerId, beerDescription, beerAbv, beerIbu, beerIcon,
beerMediumIcon,beerLargeIcon, beerGlass, beerStyle, beerStyleDescription, beerBreweryId, beerBreweryName,
beerBreweryDescription, beerBreweryYear, beerBreweryWebsite,beerBreweryIcon, beerBreweryLat, beerBreweryLong);
//add beer to list
beerList.add(thisBeer);
}
//update listview
BeerSearchAdapter adapter1 = new BeerSearchAdapter(c ,R.layout.listview_item_row, beerList);
lv.setAdapter(adapter1);
//set up clicks
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
BeerData beerInfo = beerList.get(arg2);
String idToSend = beerInfo.beerId;
//todo: launch beer fragment
listenerBeer.onArticleSelected(idToSend);
}
});
}
catch(Exception e){
}
Dialog.dismiss();
}
//todo: all the get functions go here
private String GetBeerDataFromJSON(int position, String whatToGet, JSONObject json) {
String whatIsTheKeyYouAreLookFor = whatToGet;
int whereInTheJSONArrayForLoopIsTheData = position;
String holder = "";
try{
holder = json.getJSONArray("data").getJSONObject(whereInTheJSONArrayForLoopIsTheData).getString(whatIsTheKeyYouAreLookFor);
} catch (JSONException e) {
holder = "N/A";
}
return holder;
}
//get icons
private String GetBeerBreweryIconsFromJSON(int position, String whatToGet, JSONObject json) {
String whatIsTheKeyYouAreLookFor = whatToGet;
int whereInTheJSONArrayForLoopIsTheData = position;
String holder = "";
try{
holder = json.getJSONArray("data").getJSONObject(whereInTheJSONArrayForLoopIsTheData).getJSONArray("breweries").getJSONObject(0).getJSONObject("images").getString(whatIsTheKeyYouAreLookFor);;
} catch (JSONException e) {
holder = "N/A";
}
return holder;
}
//get icons
private String GetBeerIconsFromJSON(int position, String whatToGet, JSONObject json) {
String whatIsTheKeyYouAreLookFor = whatToGet;
int whereInTheJSONArrayForLoopIsTheData = position;
String holder = "";
try{
holder = json.getJSONArray("data").getJSONObject(whereInTheJSONArrayForLoopIsTheData).getJSONObject("labels").getString(whatIsTheKeyYouAreLookFor);
} catch (JSONException e) {
holder = "N/A";
}
return holder;
}
//get style information
private String GetBeerStyleFromJSON(int position, String whatToGet, JSONObject json) {
String whatIsTheKeyYouAreLookFor = whatToGet;
int whereInTheJSONArrayForLoopIsTheData = position;
String holder = "";
try{
holder = json.getJSONArray("data").getJSONObject(whereInTheJSONArrayForLoopIsTheData).getJSONObject("style").getString(whatIsTheKeyYouAreLookFor);
} catch (JSONException e) {
holder = "N/A";
}
return holder;
}
//get location data
private String GetBeerBreweryLocationJSON(int position, String whatToGet, JSONObject json) {
String whatIsTheKeyYouAreLookFor = whatToGet;
int whereInTheJSONArrayForLoopIsTheData = position;
String holder = "";
try{
holder = json.getJSONArray("data").getJSONObject(whereInTheJSONArrayForLoopIsTheData).getJSONArray("breweries").getJSONObject(0).getJSONArray("locations").getJSONObject(0).getString(whatIsTheKeyYouAreLookFor);
} catch (JSONException e) {
holder = "N/A";
}
return holder;
}
//get brewery information
//get style information
private String GetBeerBreweryInfoFromJSON(int position, String whatToGet, JSONObject json) {
String whatIsTheKeyYouAreLookFor = whatToGet;
int whereInTheJSONArrayForLoopIsTheData = position;
String holder = "";
try{
holder = json.getJSONArray("data").getJSONObject(whereInTheJSONArrayForLoopIsTheData).getJSONArray("breweries").getJSONObject(0).getString(whatIsTheKeyYouAreLookFor);
} catch (JSONException e) {
holder = "N/A";
}
return holder;
}
//get glass
private String GetBeerGlassFromJSON(int position, JSONObject json) {
int whereInTheJSONArrayForLoopIsTheData = position;
String holder = "";
try{
holder = json.getJSONArray("data").getJSONObject(whereInTheJSONArrayForLoopIsTheData).getJSONObject("glass").getString("name");
} catch (JSONException e) {
holder = "N/A";
}
return holder;
}
public String readJSONFeed(String URL) {
StringBuilder stringBuilder = new StringBuilder();
HttpClient httpClient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(URL);
try {
HttpResponse response = httpClient.execute(httpGet);
StatusLine statusLine = response.getStatusLine();
int statusCode = statusLine.getStatusCode();
if (statusCode == 200) {
HttpEntity entity = response.getEntity();
InputStream inputStream = entity.getContent();
BufferedReader reader = new BufferedReader(
new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
stringBuilder.append(line);
}
inputStream.close();
} else {
Log.d("JSON", "Failed to download file");
}
} catch (Exception e) {
Log.d("readJSONFeed", e.getLocalizedMessage());
}
return stringBuilder.toString();
}
}
BeerSearchAdapter是：
public class BeerSearchAdapter extends ArrayAdapter<BeerData> {
Context context;
int layoutResourceId;
List<BeerData> data = null;
public BeerSearchAdapter(Context context, int layoutResourceId, List<BeerData> data) {
super(context, layoutResourceId, data);
this.layoutResourceId = layoutResourceId;
this.context = context;
this.data = data;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row = convertView;
beerHolder holder = null;
if(row == null)
{
LayoutInflater inflater = ((Activity)context).getLayoutInflater();
row = inflater.inflate(layoutResourceId, parent, false);
holder = new beerHolder();
holder.txtBrewery = (TextView)row.findViewById(R.id.beerBreweryNameList);
holder.txtTitle = (TextView)row.findViewById(R.id.beerNameList);
row.setTag(holder);
}
else
{
holder = (beerHolder)row.getTag();
}
BeerData beer = data.get(position);
holder.txtTitle.setText(beer.beerName);
holder.txtBrewery.setText(beer.beerBreweryName);
return row;
}
static class beerHolder
{
TextView txtBrewery;
TextView txtTitle;
}
}
我Search.java在接口配备形式是在这里：
public class Search extends Fragment implements SearchView.OnQueryTextListener, ReadJSONResult.OnArticleSelectedListener {
private ListView lv;
View v;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
//set layout here
v = inflater.inflate(R.layout.activity_search, container, false);
setHasOptionsMenu(true);
getActivity().setTitle("Search");
//get user information
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getActivity());
String userName = prefs.getString("userName", null);
String userID = prefs.getString("userID", null);
//todo: code body goes here
// Inflate the layout for this fragment
return v;
}
@Override
public void onCreateOptionsMenu (Menu menu, MenuInflater inflater) {
// Inflate the menu; this adds items to the action bar if it is present.
super.onCreateOptionsMenu(menu, inflater);
Log.d("click", "inside the on create");
//inflater.inflate(R.menu.main, menu);
SearchView searchView = (SearchView) menu.findItem(R.id.menu_search2).getActionView();
searchView.setIconified(false);
searchView.setOnQueryTextListener(this);
}
public boolean onQueryTextSubmit (String query) {
//toast query
//make json variables to fill
// url to make request
String url = "myURL";
try {
query = URLEncoder.encode(query, "UTF-8");
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
String jsonUrl = url + query;
//todo: get json
new ReadJSONResult(getActivity()).execute(jsonUrl);
return false;
}
@Override
public boolean onQueryTextChange(String newText) {
// TODO Auto-generated method stub
return false;
}
@Override
public void onArticleSelected(String b){
//code to execute on click
Fragment Fragment_one;
FragmentManager man= getFragmentManager();
FragmentTransaction tran = man.beginTransaction();
//todo: set to beer fragment
Fragment_one = new StylePage2();
final Bundle bundle = new Bundle();
bundle.putString("beerIDSent", b);
Fragment_one.setArguments(bundle);
tran.replace(R.id.main, Fragment_one);//tran.
tran.addToBackStack(null);
tran.commit();
}
}
让我知道如果你需要任何其他代码，我踩在这并可以使用第二双眼睛。谢谢。
ist this line called it：listenerBeer.onArticleSelected（idToSend）; – Mike
不，这是导致问题的线路。某处你必须通过调用'setOnArticleSelectedListener（...）;'来设置侦听器，但我没有看到那个代码。 –