方向不变（Actionbar和ICS）

Question

我有一个ICS和操作栏的问题。在开始时，当我改变了方向，它的工作，但现在当我改变方向，我有这样的错误：

Caused by: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment 
com.descartes.application.MainActivity$DummySectionFragment: 
make sure class name exists, is public, and has an empty constructor that is public 

Caused by: java.lang.InstantiationException: 
can't instantiate class com.descartes.application.MainActivity$DummySectionFragment; 
no empty constructor 

下面是主要代码：

public class MainActivity extends FragmentActivity implements ActionBar.TabListener { 

/** 
* The {@link android.support.v4.view.PagerAdapter} that will provide fragments for each of the 
* sections. We use a {@link android.support.v4.app.FragmentPagerAdapter} derivative, which will 
* keep every loaded fragment in memory. If this becomes too memory intensive, it may be best 
* to switch to a {@link android.support.v4.app.FragmentStatePagerAdapter}. 
*/ 
SectionsPagerAdapter mSectionsPagerAdapter; 

/** 
* The {@link ViewPager} that will host the section contents. 
*/ 
ViewPager mViewPager; 
private static int SCAN = 1; 

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

    Loc lc = new LocImpl(this); 
    Localisation loc = lc.localiser(); 
    System.out.println(loc.toString()); 
    // Create the adapter that will return a fragment for each of the three primary sections 
    // of the app. 
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 

    // Set up the action bar. 
    final ActionBar actionBar = getActionBar(); 
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 

    // Set up the ViewPager with the sections adapter. 
    mViewPager = (ViewPager) findViewById(R.id.pager); 
    mViewPager.setAdapter(mSectionsPagerAdapter); 

    // When swiping between different sections, select the corresponding tab. 
    // We can also use ActionBar.Tab#select() to do this if we have a reference to the 
    // Tab. 
    mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() { 
     @Override 
     public void onPageSelected(int position) { 
      actionBar.setSelectedNavigationItem(position); 
     } 
    }); 

    // For each of the sections in the app, add a tab to the action bar. 
    for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) { 
     // Create a tab with text corresponding to the page title defined by the adapter. 
     // Also specify this Activity object, which implements the TabListener interface, as the 
     // listener for when this tab is selected. 
     actionBar.addTab(
       actionBar.newTab() 
         .setText(mSectionsPagerAdapter.getPageTitle(i)) 
         .setTabListener(this)); 
    } 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    getMenuInflater().inflate(R.menu.activity_main, menu); 
    return true; 
} 

// Ecouteurs qui correspondent à chaque bouton présent dans la page 
public boolean onOptionsItemSelected(MenuItem item) { 
    switch (item.getItemId()) { 
     case R.id.menu_camera: 

      // app icon in action bar clicked; go home 
      Intent intent = new Intent(this, ScanBarActivity.class); 
      intent.putExtra("METHODE", "SCAN"); 
      startActivityForResult(intent, SCAN); 
      return true; 
     default: 
      return super.onOptionsItemSelected(item); 
    } 
} 


public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { 
} 

public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { 
    // When the given tab is selected, switch to the corresponding page in the ViewPager. 
    mViewPager.setCurrentItem(tab.getPosition()); 
} 

public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) { 
} 

/** 
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to one of the primary 
* sections of the app. 
*/ 
public class SectionsPagerAdapter extends FragmentPagerAdapter { 

    public SectionsPagerAdapter(FragmentManager fm) { 
     super(fm); 
    } 

    @Override 
    public Fragment getItem(int i) { 
     Fragment fragment = new DummySectionFragment(); 
     Bundle args = new Bundle(); 
     args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, i + 1); 
     fragment.setArguments(args); 
     return fragment; 
    } 

    @Override 
    public int getCount() { 
     return 4; 
    } 

    @Override 
    public CharSequence getPageTitle(int position) { 
     switch (position) { 
      case 0: return getString(R.string.title_section1).toUpperCase(); 
      case 1: return getString(R.string.title_section2).toUpperCase(); 
      case 2: return getString(R.string.title_section3).toUpperCase(); 
      case 3: return getString(R.string.title_section4).toUpperCase(); 
     } 
     return null; 
    } 
} 

/** 
* A dummy fragment representing a section of the app, but that simply displays dummy text. 
*/ 
public class DummySectionFragment extends Fragment { 
    public DummySectionFragment() { 
    } 

    public static final String ARG_SECTION_NUMBER = "section_number"; 

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

     Bundle args = getArguments(); 
     switch (args.getInt(ARG_SECTION_NUMBER)){ 
     case 1: 
      return inflater.inflate(R.layout.page_accueil, container, false); 
     case 2: 

      break; 
     case 3: 

      break; 
     case 4: 

      break; 
     } 
     TextView textView = new TextView(getActivity()); 
     textView.setGravity(Gravity.CENTER); 
     textView.setText(Integer.toString(args.getInt(ARG_SECTION_NUMBER))); 
     return textView; 

    } 
} 

} 

我不明白错误在哪里，所以我问你，你能帮我吗？

Answer 1

变化

public class DummySectionFragment extends Fragment 

到

public static class DummySectionFragment extends Fragment 

（或移动DummySectionFragment到一个单独的类文件）。