在片段中带有ListView的ViewPager-修改时listview不会更新

Question

当我从listview中添加或删除一个项目时，listview不会更新，除非我在viewpager中滚动到屏幕外，然后返回，在片段中再次触发OnCreate方法。这是基于eclipse中的viewpager模板的，我只是在片段中添加了一个listview，而不仅仅是一个textview。将notifyDataSetChanged放置到片段中没有帮助，也没有向片段中添加OnResume。以下是主要活动。adapter和listview中包含正确的项目，但只有在您滚动至少两页（在我的设备上是屏幕外的，在其他设备上可能或多或少）然后返回之前，才会显示它们。我错过了什么？

public class MainActivity extends ActionBarActivity implements ActionBar.TabListener {
SectionsPagerAdapter mSectionsPagerAdapter;
static ArrayAdapter adapter;
private static DataElementTable dataElementTable;
private static ItemTable ItemTable;
private static int currentTab = 0;
ViewPager mViewPager;

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

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

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(
            getSupportFragmentManager());

    // 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 callback (listener) for when
        // this tab is selected.
        actionBar.addTab(actionBar.newTab()
                .setText(mSectionsPagerAdapter.getPageTitle(i))
                .setTabListener(this));
    }

        dataElementTable = new DataElementTable(this);
        dataElementTable.open(); 

        itemTable = new ItemTable(this);
        itemTable.open();
     }

@Override
protected void onResume() {
  dataElementTable.open();
  itemTable.open();
  super.onResume();
}

@Override
protected void onPause() {
  dataElementTable.close();
  itemTable.close();
  super.onPause();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}


@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        addNewItem();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override
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());
}

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

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

   private void addNewItem()
    {
        AlertDialog.Builder alert = new AlertDialog.Builder(this);

        alert.setTitle("New Item");
        alert.setMessage("Enter New Item Name:");

        final EditText input = new EditText(this);
        alert.setView(input);

        alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int whichButton) {
          String value = input.getText().toString();

          Log.d("pos", "newitem " + currentTab);
          Item newItem = itemTable.createItem(currentTab - 1, value);

          }
        });

        alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
          public void onClick(DialogInterface dialog, int whichButton) {
            // Canceled.
          }
        });

        alert.show();
    }

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

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

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a PlaceholderFragment (defined as a static inner class
        // below).
        return PlaceholderFragment.newInstance(position + 1);
    }

    @Override
    public int getCount() {
        // Show 7 total pages.
        return 7;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Locale l = Locale.getDefault();
        switch (position) {
        case 0:
            return getString(R.string.title_section1).toUpperCase(l);
        case 1:
            return getString(R.string.title_section2).toUpperCase(l);
        case 2:
            return getString(R.string.title_section3).toUpperCase(l);
        case 3:
            return getString(R.string.title_section4).toUpperCase(l);
        case 4:
            return getString(R.string.title_section5).toUpperCase(l);
        case 5:
            return getString(R.string.title_section6).toUpperCase(l);
        case 6:
            return getString(R.string.title_sectionX).toUpperCase(l);
        }
        return null;
    }
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";
     ListView listView;

    /**
     * Returns a new instance of this fragment for the given section number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber)
    {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container,
                false);
        TextView textView = (TextView) rootView
                .findViewById(R.id.section_label);
        textView.setText(Integer.toString(getArguments().getInt(
                ARG_SECTION_NUMBER)));
          currentTab = (getArguments().getInt(ARG_SECTION_NUMBER)) - 1;

          listView = (ListView) rootView.findViewById(R.id.listview);
           ArrayList<String> listItems1 = new ArrayList<String>();
           ArrayList<String> listItems2 = new ArrayList<String>();
           ArrayList<String> listItems3 = new ArrayList<String>();
           ArrayList<String> listItems4 = new ArrayList<String>();
           ArrayList<String> listItems5 = new ArrayList<String>();
           ArrayList<String> listItems6 = new ArrayList<String>();    
           ArrayList<String> listItemsLog = new ArrayList<String>();



           listItems1 = itemTable.getAllItemsForCategory(0);
        listItems2 = itemTable.getAllItemsForCategory(1);
            listItems3 = itemTable.getAllItemsForCategory(2);
        listItems4 = itemTable.getAllItemsForCategory(3);
        listItems5 = itemTable.getAllItemsForCategory(4);
        listItems6 = itemTable.getAllItemsForCategory(5);


          Log.d("pos", "createview " + currentTab);
            switch (currentTab)
            {
            case 0:
            {
                adapter = new ArrayAdapter<String>(this.getActivity(), R.layout.list_item, listItems1);
            }
            break;
            case 1:
            {
                adapter = new ArrayAdapter<String>(this.getActivity(), R.layout.list_item, listItems2);
            }
            break;
            case 2:
            {
                adapter = new ArrayAdapter<String>(this.getActivity(), R.layout.list_item, listItems3);
            }
            break;
            case 3:
            {
                adapter = new ArrayAdapter<String>(this.getActivity(), R.layout.list_item, listItems4);
            }
            break;
            case 4:
            {
                adapter = new ArrayAdapter<String>(this.getActivity(), R.layout.list_item, listItems5);
            }
            break;
            case 5:
            {
                adapter = new ArrayAdapter<String>(this.getActivity(), R.layout.list_item, listItems6);
            }
            break;
            case 6:
            {
                listItemsLog = dataElementTable.getAllElements();
                adapter = new ArrayAdapter<String>(this.getActivity(), R.layout.list_item, listItemsLog);
            }
            break;
            default:
            {
                assert(false);
            }
            break;
            }

            listView.setAdapter(adapter);
            adapter.notifyDataSetChanged();     

        return rootView;
    }

}

}

Answer 1

您正在调用onCreateView方法中的notifyDataSetChanged<当您滚动查看列表视图时，会调用code>onCreateView，然后在屏幕上更新数据。更改适配器中的数据后，需要立即调用notifyDataSetChanged，而不是在onCreateView中。