我有一个加载一个新片段的按钮，但它是强制关闭时出现此错误：
java.lang.NullPointerException
at com.beerportfolio.beerportfoliopro.BPTopTastes.onCreateView(BPTopTastes.java:29)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
at android.os.Handler.handleCallback(Handler.java:730)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:5789)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:843)
at dalvik.system.NativeStart.main(Native Method)
加载新片段的按钮是：
public class Discover extends Fragment {
Fragment Fragment_one;
Fragment Fragment_two;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.activity_discover, container, false);
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getActivity());
String userName = prefs.getString("userName", null);
String userID = prefs.getString("userID", null);
//add button onclick fo top beers
Button bt = (Button)v.findViewById(R.id.discoverBeers);
bt.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// do whatever stuff you wanna do here
FragmentManager man=getFragmentManager();
FragmentTransaction tran=man.beginTransaction();
Fragment_one=new BPTopBeers();
tran.replace(R.id.main, Fragment_one);//tran.
tran.addToBackStack(null);
tran.commit();
}
});
//todo: add button onclick fo top tastes
Button bt2 = (Button)v.findViewById(R.id.discoverTaste);
bt2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// do whatever stuff you wanna do here
FragmentManager man=getFragmentManager();
FragmentTransaction tran=man.beginTransaction();
Fragment_two=new BPTopTastes();
tran.replace(R.id.main, Fragment_two);//tran.
tran.addToBackStack(null);
tran.commit();
}
});
// Inflate the layout for this fragment
//todo: change to discover layout
return v;
}
正在启动的片段是：
public class BPTopTastes extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.taste_statistics_layout, container, false);
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getActivity());
String userName = prefs.getString("userName", null);
String userID = prefs.getString("userID", null);
String title = "Top Tastes on Beer Portfolio";
TextView topTitle = (TextView) v.findViewById(R.id.topTasteTitle);
topTitle.setText(title);
//construct url
String url = "myURL";
//async task goes here
new GetTasteStatisticsJSON(getActivity()).execute(url);
// Inflate the layout for this fragment
return v;
}
}
并且正在调用的异步任务是：
public class GetTasteStatisticsJSON extends AsyncTask<String, Void, String> {
Context c;
private ProgressDialog Dialog;
public GetTasteStatisticsJSON(Context context)
{
c = context;
Dialog = new ProgressDialog(c);
}
@Override
protected String doInBackground(String... arg0) {
// TODO Auto-generated method stub
return readJSONFeed(arg0[0]);
}
protected void onPreExecute() {
Dialog.setMessage("Getting tastes");
Dialog.setTitle("Loading");
Dialog.setCancelable(false);
Dialog.show();
}
protected void onPostExecute(String result){
//decode json here
try{
JSONArray jsonArray = new JSONArray(result);
//acces listview
ListView lv = (ListView) ((Activity) c).findViewById(R.id.yourTasteStatistics);
//make array list for beer
final List<TasteInfo> tasteList = new ArrayList<TasteInfo>();
for(int i = 0; i < jsonArray.length(); i++) {
String style = jsonArray.getJSONObject(i).getString("taste");
String rate = jsonArray.getJSONObject(i).getString("rate");
int count = i + 1;
style = count + ". " + style;
Log.d("brewery stats", style);
//create object
TasteInfo tempTaste = new TasteInfo(style, rate);
//add to arraylist
tasteList.add(tempTaste);
//add items to listview
TasteInfoAdapter adapter1 = new TasteInfoAdapter(c ,R.layout.brewer_stats_listview, tasteList);
lv.setAdapter(adapter1);
//set up clicks
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
TasteInfo o=(TasteInfo)arg0.getItemAtPosition(arg2);
String tempTaste = o.taste;
//todo: load taste page fragment
//Intent myIntent = new Intent(c, TastePage.class);
// myIntent.putExtra("taste", tempTaste);
//c.startActivity(myIntent);
}
});
}
}
catch(Exception e){
}
Dialog.dismiss();
}
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();
}
}
我有点困惑，因为我在同一个片段中有另一个按钮以类似的方式启动一个新片段就好......
答案 0 :(得分：1)
我在梳理完代码后发现了自己的错误。我在这行中有错误的ID：
TextView topTitle = (TextView) v.findViewById(R.id.topTasteTitle);
因此无法找到，设置标题。
答案 1 :(得分：0)
你能检查BPTopTastes布局是否正确膨胀，因此当你调用setText（）方法时topTitle不为null。
删除异步任务时是否有效？
Eclipse调试器可以设置为在异常时暂停，这可能会给你一些指示。