Fragment Androida getArguments() zwraca wartość null

Question

Jak sugeruje tytuł.
Pobrałem kod Fragment stąd,.
To jest przykład fragmentu z oficjalnej witryny dla programistów Androida. http://developer.android.com/training/basics/fragments/fragment-ui.html

To MainActivity.java 's onCreate():

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.news_articles); 

    // Check whether the activity is using the layout version with 
    // the fragment_container FrameLayout. If so, we must add the first fragment 
    if (findViewById(R.id.fragment_container) != null) { 

     // However, if we're being restored from a previous state, 
     // then we don't need to do anything and should return or else 
     // we could end up with overlapping fragments. 
     if (savedInstanceState != null) { 
      return; 
     } 

     // Create an instance of ExampleFragment 
     HeadlinesFragment fragment = new HeadlinesFragment(); 

     // In case this activity was started with special instructions from an Intent, 
     // pass the Intent's extras to the fragment as arguments 
     //fragment.setArguments(getIntent().getExtras()); 
     Bundle args= new Bundle(); 
     args.putString("category", "clothes"); 
     args.putString("item", "shirts"); 
     fragment.setArguments(args); 

     // Add the fragment to the 'fragment_container' FrameLayout 
     getSupportFragmentManager().beginTransaction() 
       .replace(R.id.fragment_container, fragment).commit(); 
    } 
} 

I HeadlinesFragment.java' s onCreate():

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    // We need to use a different list item layout for devices older than Honeycomb 
    int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ? 
      android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1; 

    Bundle args = getArguments(); 
    if (args == null) { 
     Toast.makeText(getActivity(), "arguments is null " , Toast.LENGTH_LONG).show(); 
    } else { 
     Toast.makeText(getActivity(), "text " + args , Toast.LENGTH_LONG).show(); 
    }   

    // Create an array adapter for the list view, using the Ipsum headlines array 
    setListAdapter(new ArrayAdapter<String>(getActivity(), layout, Ipsum.Headlines)); 

} 

Czytałem kilka QA tutaj, jak ten Fragment getArguments() returns null i wiele inne związane z setArguments() i , ale nadal utknąłem.

A ja przeniósł Bundle i Toast kod do onAttach() i onCreateView() z bezskutecznie. Co jest nie tak z moim kodem? Myślę, że czegoś brakuje, ale nie wiem co to jest.
Proszę o pomoc! Dzięki.

Edytuj:
Wyrażam wyraźniej moją intencję. W pobranym fragmencie FragmentBasic znajdują się MainActivity.java, HeadlinesFragment.java i ArticleFragment.java. "Komunikacja" od MainActivity.java do ArticlesFragment.java nie jest tutaj problemem. Chcę tylko wysłać dane z MainActivity.java do HeadlinesFragment.java. Ich połączenie jest następujące:

-------------------------------------- 
| MainActivity <-> HeadlinesFragment | 
|  |        | 
|  |>> ArticlesFragment   | 
-------------------------------------- 

I HeadlinesFragment działa w środowisku wykonawczym.

* Ten kod działa, gdy używasz gadżetu Android z rozszerzeniem < o szerokości 600 pikseli. Ale nie działa podczas korzystania z tabletu (> = 600px), Jak udowodniono przez @ Tesla1984 poniżej. Ale to, czego chcę, to ten sam wynik na gadżecie < 600px i gadżecie> 600px.

Answer 1

mam rozwiązać go. Wygląda na to, że jedynym sposobem przesyłania danych z MainActivity.java do HeadlinesFragment.java jest wywołanie zwrotne (jeśli ktoś inny zna inne sposoby, proszę o przyczynianie się, to mamy inne sposoby poza tym, pomagając innym w tego rodzaju problemach).

Głównym Kod z jest funkcją MainActivity.java za public Bundle getBundle() {}, a następnie ustawić sekcję interface na HeadlinesFragment.java i dodać public Bundle getBundle(); i wreszcie wywołać ją z HeadlinesFragment.java na onCreate.

Co mnie mylić to fragment.setArguments(getIntent().getExtras()); na MainActivity.java's onCreate. Umieszczono tam ten kod i wierzę, że zadziała, ponieważ jest od oficjalnego podręcznika programisty Androida i APIhttp://developer.android.com/training/basics/fragments/fragment-ui.html, ale to nie zadziałało (teraz uważam, że fragment kodu nic nie da). Tak więc każdy, kto czyta tutorial lub próbkę, bierze to z przymrużeniem oka!

Poniższe kody, aby każdy mógł je zrozumieć.

MainActivity.java:

/* 
* Copyright (C) 2012 The Android Open Source Project 
* 
* Licensed under the Apache License, Version 2.0 (the "License"); 
* you may not use this file except in compliance with the License. 
* You may obtain a copy of the License at 
* 
*  http://www.apache.org/licenses/LICENSE-2.0 
* 
* Unless required by applicable law or agreed to in writing, software 
* distributed under the License is distributed on an "AS IS" BASIS, 
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
* See the License for the specific language governing permissions and 
* limitations under the License. 
*/ 
package com.example.android.fragments; 

import android.os.Bundle; 
import android.support.v4.app.FragmentActivity; 
import android.support.v4.app.FragmentTransaction; 
import android.widget.Toast; 

public class MainActivity extends FragmentActivity 
     implements HeadlinesFragment.OnHeadlineSelectedListener { 

    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.news_articles); 

     // Check whether the activity is using the layout version with 
     // the fragment_container FrameLayout. If so, we must add the first fragment 
     if (findViewById(R.id.fragment_container) != null) { 

      // However, if we're being restored from a previous state, 
      // then we don't need to do anything and should return or else 
      // we could end up with overlapping fragments. 
      if (savedInstanceState != null) { 
       return; 
      } 

      Toast.makeText(getApplicationContext(), "activity", Toast.LENGTH_LONG).show(); 

      // Create an instance of ExampleFragment 
      HeadlinesFragment fragment = new HeadlinesFragment(); 

      // In case this activity was started with special instructions from an Intent, 
      // pass the Intent's extras to the fragment as arguments 
      fragment.setArguments(getIntent().getExtras()); 

      // Add the fragment to the 'fragment_container' FrameLayout 
      getSupportFragmentManager().beginTransaction() 
        .replace(R.id.fragment_container, fragment).commit(); 
     } 
    } 

    public void onArticleSelected(int position) { 
     // The user selected the headline of an article from the HeadlinesFragment 

     // Capture the article fragment from the activity layout 
     ArticleFragment articleFrag = (ArticleFragment) 
       getSupportFragmentManager().findFragmentById(R.id.article_fragment); 

     if (articleFrag != null) { 
      // If article frag is available, we're in two-pane layout... 

      // Call a method in the ArticleFragment to update its content 
      articleFrag.updateArticleView(position); 

     } else { 
      // If the frag is not available, we're in the one-pane layout and must swap frags... 

      // Create fragment and give it an argument for the selected article 
      ArticleFragment newFragment = new ArticleFragment(); 
      Bundle args = new Bundle(); 
      args.putInt(ArticleFragment.ARG_POSITION, position); 
      newFragment.setArguments(args); 
      FragmentTransaction transaction = getSupportFragmentManager().beginTransaction(); 

      // Replace whatever is in the fragment_container view with this fragment, 
      // and add the transaction to the back stack so the user can navigate back 
      transaction.replace(R.id.fragment_container, newFragment); 
      transaction.addToBackStack(null); 

      // Commit the transaction 
      transaction.commit(); 
     } 
    } 

    public Bundle getBundle() { 
     Bundle args = new Bundle(); 
     args.putString("category", "cloths"); 
     args.putString("item", "shirts"); 
     return args; 
    } 
} 

HeadlinesFragment.java:

/* 
* Copyright (C) 2012 The Android Open Source Project 
* 
* Licensed under the Apache License, Version 2.0 (the "License"); 
* you may not use this file except in compliance with the License. 
* You may obtain a copy of the License at 
* 
*  http://www.apache.org/licenses/LICENSE-2.0 
* 
* Unless required by applicable law or agreed to in writing, software 
* distributed under the License is distributed on an "AS IS" BASIS, 
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
* See the License for the specific language governing permissions and 
* limitations under the License. 
*/ 
package com.example.android.fragments; 

import android.app.Activity; 
import android.os.Build; 
import android.os.Bundle; 
import android.support.v4.app.ListFragment; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 
import android.widget.Toast; 

public class HeadlinesFragment extends ListFragment { 
    OnHeadlineSelectedListener mCallback; 

    // The container Activity must implement this interface so the frag can deliver messages 
    public interface OnHeadlineSelectedListener { 
     /** Called by HeadlinesFragment when a list item is selected */ 
     public void onArticleSelected(int position); 
     public Bundle getBundle(); 
    } 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     Bundle bundle = mCallback.getBundle(); 
     Toast.makeText(getActivity(), "headline fragment " + bundle, Toast.LENGTH_LONG).show(); 

     // We need to use a different list item layout for devices older than Honeycomb 
     int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ? 
       android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1; 

     // Create an array adapter for the list view, using the Ipsum headlines array 
     setListAdapter(new ArrayAdapter<String>(getActivity(), layout, Ipsum.Headlines)); 

    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle 
        savedInstanceState) { 

     return super.onCreateView(inflater, container, savedInstanceState); 
    } 

    @Override 
    public void onStart() { 
     super.onStart(); 

     // When in two-pane layout, set the listview to highlight the selected list item 
     // (We do this during onStart because at the point the listview is available.) 
     if (getFragmentManager().findFragmentById(R.id.article_fragment) != null) { 
      getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE); 
     } 
    } 

    @Override 
    public void onAttach(Activity activity) { 
     super.onAttach(activity); 

     // This makes sure that the container activity has implemented 
     // the callback interface. If not, it throws an exception. 
     try { 
      mCallback = (OnHeadlineSelectedListener) activity; 
     } catch (ClassCastException e) { 
      throw new ClassCastException(activity.toString() 
        + " must implement OnHeadlineSelectedListener"); 
     } 
    } 

    @Override 
    public void onListItemClick(ListView l, View v, int position, long id) { 
     // Notify the parent activity of selected item 
     mCallback.onArticleSelected(position); 

     // Set the item as checked to be highlighted when in two-pane layout 
     getListView().setItemChecked(position, true); 
    } 
} 

Answer 2

Wygląda na to, że wstawiasz parę kluczy i wartości do swojego pakietu. Prawdopodobnie musisz odwołać się do wartości klucza, jak w getArguments().getString(category);

Zgodnie z dokumentami dla putString: Wstawia wartość String do mapowania tego pakietu, zastępując istniejącą wartość dla danego klucza. Każdy klucz lub wartość może mieć wartość NULL.

Parametry klucz String lub null wartość String lub null

Answer 3

@tonny

mam pobrać FragmentBasics.zip. zmieniam tylko nazwę argumentu. jest kod i pic wyniku.

główną działalność

public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.news_articles); 

    // Check whether the activity is using the layout version with 
    // the fragment_container FrameLayout. If so, we must add the first fragment 
    if (findViewById(R.id.fragment_container) != null) { 

     // However, if we're being restored from a previous state, 
     // then we don't need to do anything and should return or else 
     // we could end up with overlapping fragments. 
     if (savedInstanceState != null) { 
      return; 
     } 

     // Create an instance of ExampleFragment 
     HeadlinesFragment fragment = new HeadlinesFragment(); 

     // In case this activity was started with special instructions from an Intent, 
     // pass the Intent's extras to the fragment as arguments 
//   firstFragment.setArguments(getIntent().getExtras()); 
     //test 
     Bundle args= new Bundle(); 
     args.putString("category", "clothes"); 
     args.putString("item", "shirts"); 
     fragment.setArguments(args); 

     // Add the fragment to the 'fragment_container' FrameLayout 
     getSupportFragmentManager().beginTransaction() 
       .replace(R.id.fragment_container, fragment).commit(); 
    } 
} 

HeadlinesFragment

public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    // We need to use a different list item layout for devices older than Honeycomb 
    int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ? 
      android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1; 

    Bundle args = getArguments(); 
    if (args == null) { 
     Toast.makeText(getActivity(), "arguments is null " , Toast.LENGTH_LONG).show(); 
    } else { 
     Toast.makeText(getActivity(), "text " + args , Toast.LENGTH_LONG).show(); 
    }  

    // Create an array adapter for the list view, using the Ipsum headlines array 
    setListAdapter(new ArrayAdapter<String>(getActivity(), layout, Ipsum.Headlines)); 
} 

oto wynik

Answer 4

Miałem ten sam problem, ale go rozwiązałem :)

Mój problem polegał na tym, że miałem element <fragment android:name=""> w układzie XML Activity. Dlatego onCreate() Fragmentu został wywołany przed wywołaniami w kodzie Java, nie ustawiając w ten sposób argumentów.

Usunąłem element <fragment> z mojego układu XML i zadziałało!