Question

我左侧的抽屉导航视图连接到具有不同视图的不同片段。结构如下。

MainActivity 抽屉导航视图

| Fragment A  -- ViewPagerA ----Tab1 - Fragment1
                                Tab2 - Fragment2
|                               Tab3 - Fragment3

| Fragment B -- ViewPagerB ----Tab1 - Fragment4
                               Tab2 - Fragment5
|                              Tab3 - Fragment6

Fragment1-6是列表视图片段。

问题是当我从片段A切换到片段B时，viewpager将从Fragment1缓存列表视图的内容，并尝试向Fragment4的适配器显示缓存的内容。因此，当我第一次从导航抽屉切换片段时，它总是显示错误的信息。

我的代码：

MainActivity：

    public class MainActivity extends Activity {
  @InjectView(R.id.navigation_view) public NavigationView mNavigationView;
    @InjectView(R.id.drawerLayout) public DrawerLayout mDrawerLayout;
//......Layout injections..............///
 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

  mDrawerToggle = new ActionBarDrawerToggle(this,mDrawerLayout, mToolbar,R.string.app_name,
                R.string.app_name){

             /** Called when a drawer has settled in a completely closed state. */
             public void onDrawerClosed(View view) {


super.onDrawerClosed(view);
         }

         /** Called when a drawer has settled in a completely open state. */
         public void onDrawerOpened(View drawerView) {
             super.onDrawerOpened(drawerView);
         }
     };

}


  public void setUpToggle()
    {


        mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {

            // This method will trigger on item Click of navigation menu
            @Override
            public boolean onNavigationItemSelected(MenuItem menuItem) {


                if (menuItem.isChecked()) menuItem.setChecked(false);
                else menuItem.setChecked(true);

                //Closing drawer on item click
                mDrawerLayout.closeDrawers();

            switch (menuItem.getItemId()) {



                    case R.id.a_drawer:
                        startFragment(FragmentA.newInstance());
                        return true;

                   case R.id.b_drawer:
                        startFragment(FragmentB.newInstance());
                        return true;



     default:
   Toast.makeText(getApplicationContext(),"More things need to be added",Toast.LENGTH_SHORT).show();
                            return true;

                }
            }
        });


        mDrawerLayout.setDrawerListener(mDrawerToggle);


            mDrawerToggle.syncState();
}
}

片段A / B（完全相同的结构和布局）

public class TabFragment extends Fragment {

public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = n; //n is any positive integer
private Context mContext;


@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    /**
     *Inflate tab_layout and setup Views.
     */

    View tabView =  inflater.inflate(R.layout.fragment_tab,null);
    tabLayout = (TabLayout) tabView.findViewById(R.id.tabs);
    viewPager = (ViewPager) tabView.findViewById(R.id.viewpager);

    viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));



    tabLayout.post(new Runnable() {
        @Override
        public void run() {
            tabLayout.setupWithViewPager(viewPager);

        }
    });
    return tabView;

}



class MyAdapter extends FragmentStatePagerAdapter{

    public MyAdapter(FragmentManager fm) {
        super(fm);


    }


    @Override
    public Fragment getItem(int position)
    {
        switch (position){
            case 0 : return  new Fragment1();//or Fragment4 5 6 here
            case 1 : return new  Fragment2();
            case 2 : return new  Fragment3();

            default:return new Fragment1();

        }
    }

    @Override
    public int getCount() {

        return int_items;

    }



    @Override
    public CharSequence getPageTitle(int position) {

        switch (position){
            case 0 :
                return "F1";
            case 1 :
                return  "F2";
            case 2 :
                return "F3";

        }
        return null;
    }
}

片段1 - 6：

public class TabFocusFragmentextends extends Fragment
implements LoaderManager.LoaderCallbacks<Cursor>


{


private TabFocusAdapter mAdapter;
private List<E> mList;

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

    loadData();// never been executed,:(
    setHasOptionsMenu(true);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_tab_focus, container, false);

    loadData();
    setupRecyclerView();
    return view;
}

@Override
public void onResume() {
    super.onResume();
}



    @Override
    public void onLoadMore() {
if(NeedLoad)
       loadData();
    }

    private void loadData() {
        //RequestData
    ……
}


private void setupRecyclerView() {
  …...

}

@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
    return new CursorLoader(mActivity, ContentProvider.createUri(E.class, null),
            null, null, null, null);
}

@Override //fragment starts here, why??
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {


    if (loadedList.size() > 0) {
     //crashes here …...

    if (!fullPacketLoaded) {
    }
}

@Override
public void onLoaderReset(Loader<Cursor> loader) {

}

如果新的片段列表适配器没有适合显示以前的内容，它将崩溃。

基于这个问题，如果您对下面的问题有更好的解决方案吗？ Why is Tablayout and Viewpager crashing with NullpointerException when I start a fragment with LoaderManager from TabFragment?

Answer 1

终于修好了。

在我的onCreate（）方法中，哪个片段实现了LoaderManager，我做了这个

  getLoaderManager().initLoader(0, null, this);
        if(!getLoaderManager().getLoader(0).isReset()) {
            getLoaderManager().restartLoader(0, null, this);
        }

当新加载程序未正确激活时，它可以正常工作。

抽屉NavigationView +片段与viewpager，如何避免在导航抽屉中的片段从一个切换到另一个时缓存数据？

1 个答案: