我对 ICS 和操作栏有疑问。一开始，当我改变方向时，它起作用了，但是现在当我改变方向时，我有这个错误：
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
这是主要代码：
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？