フラグメントとクラッシュを使用するときにAsyncTaskがnull値を返すときにRecyclerviewが正しく動作する

Question

次のコードはすべてアクティビティで正しく動作していますが、フラグメントを使用しようとすると、 AsyncTaskクラスを正しく実行しないでください。クラッシュし、APIから入力ストリーム値が取得されませんでした。私の問題に関連する別の記事を検索しましたが、ここをクリックして助言を受けたいのですが、ここで私のコードは次のようになります：

activity_main.xmlファイルコード行（フラグメントが追加されるコンテナまたは）それに置き換え：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:id="@+id/mainactivity_container" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    android:orientation="vertical" 
     tools:context="com.example.prof_mohamedatef.tabletfragments.MainActivity"> 

</LinearLayout> 

main_fragment.xmlファイルのコード行：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:orientation="vertical" 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 

<android.support.v7.widget.RecyclerView 
    android:id="@+id/card_recycler_view" 
    android:scrollbars="vertical" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"/> 

</LinearLayout> 

MainActivity JavaファイルMainFragmentレイアウトと活性に対する容器との間のbeginTransactionは次のように

package com.example.prof_mohamedatef.tabletfragments; 

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 

public class MainActivity extends AppCompatActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     MainFragment mainFragment=new MainFragment(); 
     getFragmentManager().beginTransaction() 
       .add(R.id.mainactivity_container,mainFragment) 
       .commit(); 
    } 
} 

活動に膨張しているMainFragment Javaファイル：

package com.example.prof_mohamedatef.tabletfragments; 

import android.os.AsyncTask; 
import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.support.v7.widget.GridLayoutManager; 
import android.support.v7.widget.RecyclerView; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 
import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.InputStreamReader; 
import java.net.HttpURLConnection; 
import java.net.URL; 
import java.util.ArrayList; 


/** 
* Created by Prof-Mohamed Atef on 9/8/2016. 
*/ 
public class MainFragment extends android.app.Fragment{ 

private static final String TAG = "RecyclerViewFragment"; 

public MainFragment() {} 

RecyclerView mRecyclerView; 
public ImagesAdapter mAdapter; 

ArrayList<MovieEntity> list = new ArrayList<MovieEntity>(); 

final String now = "http://api.themoviedb.org/3/movie/popular?api_key=868bebbf76a3831f11b3985c703cf959"; 

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

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, 
         @Nullable ViewGroup container, 
         @Nullable Bundle savedInstanceState) { 
    View rootView=inflater.inflate(R.layout.main_fragment,container,false); 
    rootView.setTag(TAG); 
    mRecyclerView = (RecyclerView)rootView.findViewById(R.id.card_recycler_view); 
// mRecyclerView.setHasFixedSize(true); 
    RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getActivity(), 2); 
    mRecyclerView.setLayoutManager(layoutManager); 
    mRecyclerView.setAdapter(mAdapter); 
    return rootView; 
} 

private void update_START() { 
    Fetch_Moview_data f_m_data = new Fetch_Moview_data(); 
    f_m_data.execute(now); 
} 

public String main_List = "results"; 
public String POSTER_PATH = "poster_path"; 
public String VIDEO_ID = "id"; 
public String TITLE = "title"; 
public String OVERVIEW = "overview"; 
public String RELEASE_DATE = "release_date"; 
public String POPULARITY = "popularity"; 
public String VOTE_AVERAGE_="vote_average"; 

public String POSTER_PATH_STRING; 
public String VIDEO_ID_STRING; 
public String TITLE_STRING; 
public String OVERVIEW_STRING; 
public String RELEASE_DATE_STRING; 
public String POPULARITY_STRING; 
public String VOTE_AVERAGE_STRING; 

public JSONObject MoviesJson; 
public JSONArray moviesDataArray; 
public JSONObject oneMovieData; 

public class Fetch_Moview_data extends AsyncTask<String, Void, ArrayList<MovieEntity>> { 

    private final String LOG_TAG = Fetch_Moview_data.class.getSimpleName(); 

    private ArrayList<MovieEntity> getMovieDataFromJson(String MoviesJsonStr) 
      throws JSONException { 

     MoviesJson = new JSONObject(MoviesJsonStr); 
     moviesDataArray = MoviesJson.getJSONArray(main_List); 

     list.clear(); 
     for (int i = 0; i < moviesDataArray.length(); i++) { 

      // Get the JSON object representing a movie per each loop 
      oneMovieData = moviesDataArray.getJSONObject(i); 

      POSTER_PATH_STRING = oneMovieData.getString(POSTER_PATH); 
      VIDEO_ID_STRING = oneMovieData.getString(VIDEO_ID); 
      TITLE_STRING = oneMovieData.getString(TITLE); 
      OVERVIEW_STRING = oneMovieData.getString(OVERVIEW); 
      RELEASE_DATE_STRING = oneMovieData.getString(RELEASE_DATE); 
      POPULARITY_STRING = oneMovieData.getString(POPULARITY); 
      VOTE_AVERAGE_STRING=oneMovieData.getString(VOTE_AVERAGE_); 

      mAdapter=null; 
      MovieEntity entity = new MovieEntity(POSTER_PATH_STRING, VIDEO_ID_STRING, TITLE_STRING, OVERVIEW_STRING, RELEASE_DATE_STRING, POPULARITY_STRING,VOTE_AVERAGE_STRING); 
      list.add(entity); 
     } 

     return list; 
    } 

    @Override 
    protected ArrayList<MovieEntity> doInBackground(String... params) { 

     String Movies_images_JsonSTR = null; 

     HttpURLConnection urlConnection = null; 
     BufferedReader reader = null; 

     if (params.length == 0) { 
      return null; 
     } 

     try { 

      URL url = new URL(params[0]); 
      urlConnection = (HttpURLConnection) url.openConnection(); 

      urlConnection.setRequestMethod("GET"); 
      urlConnection.connect(); 

      InputStream inputStream = urlConnection.getInputStream(); 
      StringBuffer buffer = new StringBuffer(); 
      if (inputStream == null) { 
       Movies_images_JsonSTR = null; 
      } 

      reader = new BufferedReader(new InputStreamReader(inputStream)); 
      String line; 
      while ((line = reader.readLine()) != null) { 
       buffer.append(line + "\n"); 
      } 
      if (buffer.length() == 0) { 
       return null; 
      } 

      Movies_images_JsonSTR = buffer.toString(); 

      Log.v(LOG_TAG, "Movies JSON String: " + Movies_images_JsonSTR); 
     } catch (IOException e) { 
      Log.e(LOG_TAG, "Error here Exactly ", e); 

      return null; 
     } finally { 
      if (urlConnection != null) { 
       urlConnection.disconnect(); 
      } 
      if (reader != null) { 
       try { 
        reader.close(); 
       } catch (final IOException e) { 
        Log.e(LOG_TAG, "Error closing stream", e); 
       } 
      }else { 
       Log.v(LOG_TAG, "Reader = null (No Input Stream) "); 
      } 
     } 
     try { 
      return getMovieDataFromJson(Movies_images_JsonSTR); 
     } catch (JSONException e) { 
      Log.e(LOG_TAG, "didn't got Movies Data from getJsonData method", e); 
      e.printStackTrace(); 
     } 
     return null; 
    } 

    @Override 
    protected void onPostExecute(ArrayList<MovieEntity> result) { 
     mAdapter=null; 
     list=result; 
     mAdapter = new ImagesAdapter(getContext(), result); 
     mRecyclerView.setAdapter(mAdapter); 
    } 
} 
} 

編集 は問題がAsyncTask自体ではないが、しかし、それはからの動画データをフェッチしていませんオンラインAPIが、ここで使用されているFragmentに関連する問題ですが、デバッガはExceptionの型を識別しませんが、サーバに接続していないことを識別できます。したがって、返されたInputStream、StringBuffer、 JsonStringはnull値です。

アクティビティクラスファイルのonCreateメソッドでrecyclerviewを初期化しても、APIから要求されたJson String Arrayを取得せずにアプリケーションがクラッシュすると、同じコードが正しく動作しています。非同期タスクでクラッシュします。 recyclerviewをうまく表示するために問題がどこにあるのか、そして何が必要なのかについての情報がありがたいです。前もって感謝します。

秒編集

E/dalvikvm: **Could not find class 'android.util.ArrayMap'**, referenced from method com.android.tools.fd.runtime.MonkeyPatcher.monkeyPatchExistingResources 
09-09 21:04:48.351 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve check-cast 2079 (Landroid/util/ArrayMap;) in Lcom/android/tools/fd/runtime/MonkeyPatcher; 
09-09 21:04:48.351 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x1f at 0x0258 
09-09 21:04:48.361 26794-26794/com.example.prof_mohamedatef.tabletfragments E/dalvikvm: Could not find class 'android.util.ArrayMap', referenced from method com.android.tools.fd.runtime.MonkeyPatcher.pruneResourceCacheandroid.app.Fragment.setAllowEnterTransitionOverlap, referenced from method com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super 
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve virtual method 377: Landroid/app/Fragment;.setAllowEnterTransitionOverlap (Z)V 
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x6f at 0x03d8 
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments I/dalvikvm: **Could not find method android.app.Fragment.onInflate**, referenced from method com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super 
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve virtual method 358: Landroid/app/Fragment;.onInflate (Landroid/content/Context;Landroid/util/AttributeSet;Landroid/os/Bundle;)V 
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x6f at 0x0468 
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments I/dalvikvm: Could not find method android.app.Fragment.getEnterTransition, referenced from method com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super 
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve virtual method 311: Landroid/app/Fragment;.getEnterTransition()Landroid/transition/Transition; 
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x6f at 0x0499 
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments E/dalvikvm: **Could not find class 'android.transition.Transition', referenced from method** com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super 
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve check-cast 2075 (Landroid/transition/Transition;) in Lcom/example/prof_mohamedatef/tabletfragments/MainFragment; 
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x1f at 0x04b5 
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments I/dalvikvm: Could not find method **android.app.Fragment.getAllowEnterTransitionOverlap**, referenced from method com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super 
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve virtual method 306: Landroid/app/Fragment;.getAllowEnterTransitionOverlap()Z 
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x6f at 0x04c9 

お知らせそれらの太字フォーマットの行は、それが何を意味するのか、DOS、これは私がlogCatでこのクラッシュから得ることができる唯一の参照です。その他の例外タイプはありません。

サード編集

09-11 14:25:14.968 3547-3714/com.example.prof_mohamedatef.tabletfragments E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1 
                         Process: com.example.prof_mohamedatef.tabletfragments, PID: 3547 
                         java.lang.RuntimeException: An error occurred while executing doInBackground() 
                          at android.os.AsyncTask$3.done(AsyncTask.java:309) 
                          at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354) 
                          at java.util.concurrent.FutureTask.setException(FutureTask.java:223) 
                          at java.util.concurrent.FutureTask.run(FutureTask.java:242) 
                          at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234) 
                          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
                          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
                          at java.lang.Thread.run(Thread.java:818) 
                         Caused by: java.lang.SecurityException: Permission denied (missing INTERNET permission?) 
                          at java.net.InetAddress.lookupHostByName(InetAddress.java:464) 
                          at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252) 
                          at java.net.InetAddress.getAllByName(InetAddress.java:215) 
                          at com.android.okhttp.internal.Network$1.resolveInetAddresses(Network.java:29) 
                          at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188) 
                          at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157) 
                          at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100) 
                          at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357) 
                          at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340) 
                          at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330) 
                          at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248) 
                          at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433) 
                          at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114) 
                          at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:175) 
                          at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:125) 
                          at android.os.AsyncTask$2.call(AsyncTask.java:295) 
                          at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
                          at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)  
                          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)  
                          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)  
                          at java.lang.Thread.run(Thread.java:818)  
                         Caused by: android.system.GaiException: android_getaddrinfo failed: EAI_NODATA (No address associated with hostname) 
                          at libcore.io.Posix.android_getaddrinfo(Native Method) 
                          at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:55) 
                          at java.net.InetAddress.lookupHostByName(InetAddress.java:451) 
                          at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252)  
                          at java.net.InetAddress.getAllByName(InetAddress.java:215)  
                          at com.android.okhttp.internal.Network$1.resolveInetAddresses(Network.java:29)  
                          at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188)  
                          at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157)  
                          at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100)  
                          at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357)  
                          at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340)  
                          at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330)  
                          at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)  
                          at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433)  
                          at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114)  
                          at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:175)  
                          at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:125)  
                          at android.os.AsyncTask$2.call(AsyncTask.java:295)  
                          at java.util.concurrent.FutureTask.run(FutureTask.java:237)  
                          at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)  
                          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)  
                          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)  
                          at java.lang.Thread.run(Thread.java:818)  
                         Caused by: android.system.ErrnoException: android_getaddrinfo failed: EACCES (Permission denied) 
                          at libcore.io.Posix.android_getaddrinfo(Native Method)  
                          at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:55)  
                          at java.net.InetAddress.lookupHostByName(InetAddress.java:451)  
                          at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252)  
                          at java.net.InetAddress.getAllByName(InetAddress.java:215)  
                          at com.android.okhttp.internal.Network$1.resolveInetAddresses(Network.java:29)  
                          at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188)  
                          at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157)  
                          at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100)  
                          at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357)  
                          at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340)  
                          at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330)  
                          at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)  
                          at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433)  
                          at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114)  
                          at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:175)  
                          at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:125)  
                          at android.os.AsyncTask$2.call(AsyncTask.java:295)  
                          at java.util.concurrent.FutureTask.run(FutureTask.java:237)  
                          at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)  
                          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)  
                          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)  
                          at java.lang.Thread.run(Thread.java:818)  

エラーのこの行のソリューションExactely：

Caused by: java.lang.SecurityException: Permission denied (missing INTERNET permission?) 

Answer 1

私は私のマニフェストのインターネットアクセス権がありませんでしたが働いていた場合、私に教えてください、ちょうど追加：

<uses-permission android:name="android.permission.INTERNET" /> 

すべてが、その後正しく

Answer 2

エラーは非常に簡単です： は、クラスのandroid.utilが見つかりませんでした。 ArrayMapは、コンパイラが必要とするアンドロイドクラスを見つけることができなかったことを意味します。これは推論やコードではエラーではありませんが、セットアップ上の問題です。ことをダブルチェック：アプリのbuild.gradleに

1. あなたのSDKのパスが
2. あなたのライブラリやSDKレベルが（SDKマネージャの内側）に更新されている正しい
3. 、あなたのdefaultConfigは、少なくともAPIレベル20を標的にしてコンパイルされます
4. appcompatライブラリを使用している場合は、欠落しているすべてのクラスのインポートをimport android.util.ArrayMap;からimport android.support.v4.util.ArrayMap;に変更します。

それは