Androidのフラグメントの変更の向きとNullPointerExceptionが

Question

私は、フラグメントでアプリを作成してみてください、しかし、私はいくつかのエラーを持っている：

FATAL EXCEPTION: main Process: pl.pionas.zabawa, PID: 3074 java.lang.NullPointerException at pl.pionas.zabawa.Fragments.HomeFragment.initializeListViewPromo(HomeFragment.java:77) at pl.pionas.zabawa.Fragments.HomeFragment.OnTaskCompletedArticlesPromo(HomeFragment.java:71) at pl.pionas.zabawa.AsyncTasks.ArticlesPromoAsyncTask$1.onResponse(ArticlesPromoAsyncTask.java:70) at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68) at android.os.Handler.handleCallback(Handler.java:733) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5017) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) at dalvik.system.NativeStart.main(Native Method)

私はクラスのフラグメント（例えば、LoginFragment.classに行く）と向きを変えたときに、このエラーがあります。

マイMainMenuActivity.class：

public class MainActivity extends AppCompatActivity { 
    private DrawerLayout mDrawer; 
    private Toolbar toolbar; 
    private NavigationView nvDrawer; 
    private ActionBarDrawerToggle drawerToggle; 
    private Fragment fragment = null; 
    private Boolean restore = false; 
    private String mTitle; 
    FragmentManager fragmentManager; 
    private Boolean action = false; 
    String tag = null; 
    private int prev; 
    private ArrayList<MenuFragment> mapMenu = new ArrayList<MenuFragment>(); 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     fragmentManager = getSupportFragmentManager(); 
     if (savedInstanceState != null) { 
      fragment = fragmentManager.getFragment(savedInstanceState, "currentFragment"); 
      restore = savedInstanceState.getBoolean("restore"); 
      mTitle = savedInstanceState.getString("mTitle"); 
      mapMenu = savedInstanceState.getParcelableArrayList("mapMenu"); 
      tag = fragment.getTag(); 
     } else { 
      fragment = new HomeFragment(); 
      mapMenu.add(new MenuFragment(getString(R.string.app_name), 0)); 
      restore = false; 
      mTitle = getString(R.string.app_name); 
      tag = mTitle; 
     } 

     if (fragment != null) { 
      fragmentManager.beginTransaction().replace(R.id.flContent, fragment, tag).addToBackStack(tag).commit(); 

      if (restore) { 
       fragmentManager.findFragmentByTag(tag); 
      } else { 
       fragmentManager.beginTransaction().replace(R.id.flContent, fragment, tag).addToBackStack(tag).commit(); 
      } 
     } 
     // Set a Toolbar to replace the ActionBar. 
     toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 
     getSupportActionBar().setTitle(mTitle); 

     // Find our drawer view 
     mDrawer = (DrawerLayout) findViewById(R.id.drawer_layout); 

     drawerToggle = new ActionBarDrawerToggle(this, mDrawer, toolbar, R.string.drawer_open, R.string.drawer_close); 

     // Tie DrawerLayout events to the ActionBarToggle 
     mDrawer.addDrawerListener(drawerToggle); 

     nvDrawer = (NavigationView) findViewById(R.id.nvView); 

     View headerLayout = nvDrawer.inflateHeaderView(R.layout.nav_header); 
     // We can now look up items within the header if needed 
     ImageView ivHeaderPhoto = (ImageView) headerLayout.findViewById(R.id.imageView); 
     Drawable myDrawable = ResourcesCompat.getDrawable(getResources(), R.drawable.logo, null); 
     ivHeaderPhoto.setImageDrawable(myDrawable); 

     // Setup drawer view 
     setupDrawerContent(nvDrawer); 

    } 


    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // The action bar home/up action should open or close the drawer. 
     switch (item.getItemId()) { 
      case android.R.id.home: 
       mDrawer.openDrawer(GravityCompat.START); 
       return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 

    // `onPostCreate` called when activity start-up is complete after `onStart()` 
    // NOTE! Make sure to override the method with only a single `Bundle` argument 
    @Override 
    protected void onPostCreate(Bundle savedInstanceState) { 
     super.onPostCreate(savedInstanceState); 
     // Sync the toggle state after onRestoreInstanceState has occurred. 
     drawerToggle.syncState(); 
    } 

    @Override 
    public void onConfigurationChanged(Configuration newConfig) { 
     super.onConfigurationChanged(newConfig); 
     // Pass any configuration change to the drawer toggles 
     drawerToggle.onConfigurationChanged(newConfig); 
    } 

    private void setupDrawerContent(NavigationView navigationView) { 
     navigationView.setNavigationItemSelectedListener(
       new NavigationView.OnNavigationItemSelectedListener() { 
        @Override 
        public boolean onNavigationItemSelected(MenuItem menuItem) { 
         selectDrawerItem(menuItem); 
         return true; 
        } 
       }); 
    } 

    public void selectDrawerItem(MenuItem menuItem) { 
     int menuId = menuItem.getItemId(); 
     if (prev == menuId) { 
      mDrawer.closeDrawers(); 
      return; 
     } 
     prev = menuId; 

     createNewFragment(menuId, true); 

    } 

    private void createNewFragment(int menuId, boolean add) { // Create a new fragment and specify the fragment to show based on nav item clicked 
     Class fragmentClass; 
     action = true; 
     int position = 0; 
     switch (menuId) { 
      case R.id.nav_login: 
       fragmentClass = LoginFragment.class; 
       mTitle = getString(R.string.menu_login); 
       position = 1; 
       break; 

      case R.id.nav_articles: 
       fragmentClass = CategoryFragment.class; 
       mTitle = getString(R.string.menu_articles); 
       position = 2; 
       break; 

      default: 
       fragmentClass = HomeFragment.class; 
       mTitle = APP_NAME; 
       break; 
     } 

     if (add) { 
      mapMenu.add(new MenuFragment(mTitle, menuId)); 
     } 

     try { 
      fragment = (Fragment) fragmentClass.newInstance(); 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
     tag = mTitle; 
     if (action) { 
      // Insert the fragment by replacing any existing fragment 
      fragmentManager.beginTransaction().replace(R.id.flContent, fragment, tag).addToBackStack(tag).commit(); 

      // Highlight the selected item has been done by NavigationView 
      nvDrawer.getMenu().getItem(position).setChecked(true); 
     } 
     // Set action bar title 
     getSupportActionBar().setTitle(mTitle); 
     // Close the navigation drawer 
     mDrawer.closeDrawers(); 
    } 

    @Override 
    protected void onSaveInstanceState(Bundle outState) { 
     super.onSaveInstanceState(outState); 
     outState.putBoolean("restore", true); 
     outState.putParcelableArrayList("mapMenu", mapMenu); 
     outState.putString("mTitle", getSupportActionBar().getTitle().toString()); 
     getSupportFragmentManager().putFragment(outState, "currentFragment", fragment); 
    } 

    @Override 
    public void onBackPressed() { 
     DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
     if (drawer.isDrawerOpen(GravityCompat.START)) { 
      drawer.closeDrawer(GravityCompat.START); 
     } else { 
      int i = mapMenu.size(); 
      if (i > 1) { 
       mapMenu.remove(i - 1); 
       MenuFragment menuFragment = mapMenu.get((i - 2)); 
       tag = menuFragment.getTitle(); 
       createNewFragment(menuFragment.getMenuPosition(), false); 
      } else { 
       MainActivity.this.finish(); 
      } 
     } 
    } } 

マイHomeFragment.class：私が間違って何

public class HomeFragment extends Fragment implements OnTaskCompletedArticlesLastAdded { 
    private ListView listViewLastAdded; 
    private ArrayList<Article> articleLastAddedList; 

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

     ArticlesLastAddedAsyncTask articlesLastAddedAsyncTask = new ArticlesLastAddedAsyncTask(getContext(), this); 
     articlesLastAddedAsyncTask.execute(); 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_home, container, false); 
     listViewLastAdded = (ListView) rootView.findViewById(R.id.listViewLastAdded); 
     return rootView; 
    } 

    @Override 
    public void OnTaskCompletedArticlesLastAdded(ArrayList<Article> articleList) { 
     articleLastAddedList = articleList; 
     initializeListLastAdded(); 
    } 

    private void initializeListLastAdded() { 
     ArticlesListAdapter adapter = new ArticlesListAdapter(getContext(), articleLastAddedList); 
     listViewLastAdded.setAdapter(adapter); 
    } 

} 

？ ありがとうございます。

Answer 1

あなたは、画面を回転させたときにAndroidが活動を再開したくない場合は、あなたのAndroidManifest.xml

で活動タグ内

android:configChanges="orientation|screenSize" 

を追加することができます（これはあなたのフラグメントを破棄し、nullポインタ例外が発生します）