Question

我遇到了ICS和Actionbar的问题。一开始，当我改变方向时，它有效，但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，你能帮助我吗？

Answer 1

更改

public class DummySectionFragment extends Fragment

到

public static class DummySectionFragment extends Fragment

（或将DummySectionFragment移动到单独的类文件中。）

方向不会改变（Actionbar和ICS）

1 个答案: