问题
Hi I am trying to make application that has view pager and tablayout. So when I choose 'friends' tab layout it will call java class named FragFriends.java,
In this class I want to inflate layout where recycler view adapter is filled with data from database that I retrieve using asynctask method in class PHPuserlist.java
However my application suddenly stopped
Here is the the FragFriends.java
public class FragmentFriends extends Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View rootview = inflater.inflate(R.layout.activity_user_view,container,false);// The activity that contains recyclerview
View dview = inflater.inflate(R.layout.activity_profile,container,false); //This is the activity that contains tablayout
PHPUserList phpUserList = new PHPUserList(dview.getContext());
phpUserList.execute();
return rootview;
}
}
I have implement this recycler view with intent and it work just fine. But I need to use this with fragment Pleas help me
This is the logcat
05-27 16:55:12.198 14031-14031/com.rumahdosen.www.rumahdosen E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.rumahdosen.www.rumahdosen, PID: 14031
java.lang.NullPointerException
at com.rumahdosen.www.rumahdosen.PHPUserList.onPreExecute(PHPUserList.java:82)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
at android.os.AsyncTask.execute(AsyncTask.java:535)
at com.rumahdosen.www.rumahdosen.FragmentFriends.onCreateView(FragmentFriends.java:20)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:570)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1177)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1025)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1545)
at android.view.View.measure(View.java:16834)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:824)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:500)
at android.view.View.measure(View.java:16834)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5374)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:340)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:16834)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5374)
at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:391)
at android.view.View.measure(View.java:16834)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5374)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:340)
at android.view.View.measure(View.java:16834)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5374)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1621)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:742)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:607)
at android.view.View.measure(View.java:16834)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5374)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:340)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2332)
at android.view.View.measure(View.java:16834)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2252)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1315)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1513)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1192)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6231)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:788)
at android.view.Choreographer.doCallbacks(Choreographer.java:591)
at android.view.Choreographer.doFrame(Choreographer.java:560)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:774)
at android.os.Handler.handleCallback(Handler.java:808)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5292)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:824)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:640)
at dalvik.system.NativeStart.main(Native Method)
Below is the PHPUserList.java
public class PHPUserList extends AsyncTask<Void,UserList,Void> {
private Context context;
Activity activity;
RecyclerView recyclerView;
RecyclerView.Adapter adapter;
RecyclerView.LayoutManager layoutManager;
ArrayList<UserList> arrayList = new ArrayList<>();
PHPUserList(Context ctx){
this.context = ctx;
activity = (Activity)ctx;
}
@Override
protected Void doInBackground(Void... params) {
try {
URL url = new URL("http://njtwicomp.pe.hu/listuser.php");
HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder stringBuilder = new StringBuilder();
String line;
while ((line = bufferedReader.readLine())!=null)
{
stringBuilder.append(line+"\n");
}
httpURLConnection.disconnect();
String json_string = stringBuilder.toString().trim();
JSONObject jsonObject = new JSONObject(json_string);
JSONArray jsonArray = jsonObject.getJSONArray("server_response");
int count = 0;
while(count<jsonArray.length()){
JSONObject JO = jsonArray.getJSONObject(count);
count++;
UserList userList = new UserList(JO.getString("Name"),JO.getString("Username"));
publishProgress(userList);
}
Log.d("JSON STRING", json_string);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPreExecute() {
recyclerView = (RecyclerView) activity.findViewById(R.id.RVUserList);
layoutManager = new LinearLayoutManager(context);
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(true);
adapter = new RecyclerAdapter(arrayList);
recyclerView.setAdapter(adapter);
}
@Override
protected void onProgressUpdate(UserList... values) {
arrayList.add(values[0]);
adapter.notifyDataSetChanged();
}
@Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
}
}
I try to find the recyclerview by id in another activity while I set the activity as the activity of the passed context. But I don't know how to fix that
So how do I get the activity which is not the context that I passed in asynctask?
回答1:
Change this:
PHPUserList phpUserList = new PHPUserList(dview.getContext());
phpUserList.execute();
to :
new PHPUserList(getActivity()).execute();
回答2:
In your fragment class just put getActivity(), where Context is needed it will do the job!
回答3:
just use getContext();
This does the work.
In case you need to use the Activity Context then Have static context of ClassName.this
来源：https://stackoverflow.com/questions/37479347/android-how-to-pass-another-activity-application-context-from-java-class-exten