java - ViewPager 与 AsyncTaskLoader

Question

好吧，我很难理解我的应用程序出了什么问题。所以我有带有这样的选项卡的 ViewPager:

适配器.java

public class CustomPagerAdapter extends FragmentPagerAdapter {

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

@Override
public Fragment getItem(int position) {
    switch (position) {
        case 0:
            return new Fragment1();
        case 1:
            return new Fragment2();

        // And so on...

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

这是 xml:

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.env.test.app.MainActivity" />

主要 Activity :

public class MainActivity extends FragmentActivity implements ActionBar.TabListener {

static final String[] tabTitles = {"test1","test2","test3","tes3"};
CustomPagerAdapter adapter;
ViewPager viewPager;
ActionBar actionBar;

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

    adapter = new CustomPagerAdapter(getSupportFragmentManager());
    actionBar = getActionBar();
    viewPager = (ViewPager) findViewById(R.id.pager);

    viewPager.setAdapter(adapter);
    actionBar.setHomeButtonEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    for (String tabTitle : tabTitles) {
        actionBar.addTab(actionBar.newTab().setText(tabTitle).setTabListener(this));

    }

    viewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {

        @Override
        public void onPageSelected(int position) {
            actionBar.setSelectedNavigationItem(position);
        }

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            super.onPageScrolled(position, positionOffset, positionOffsetPixels);
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            super.onPageScrollStateChanged(state);
        }
    });
} // And 3 more implemented methods of tabs...

在每一个 fragment 中，我都使用 Jsoup scrape 和 CardListView 填充来调用 AsyncTaskLoader。现在一切正常，但假设我在第 1 页。我滑入第3页。然后我滑回 page1，内容 (ListView) 就消失了。现在我再次滑动到第3页或第4页，也没有内容。所以，长话短说，我正在丢失数据(尝试过 AsyncTask，但我更喜欢加载程序，问题是相同的，所以我不认为问题出在加载程序中)。然而，这是其中一个 fragment :

public class Fragment1 extends Fragment implements LoaderManager.LoaderCallbacks<ArrayList<Card>> {

SharedPreferences accountData;
String accountID, accountPassword;

public Fragment1() {

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment1, container, false);
    return view;
}

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

    accountData = getActivity().getSharedPreferences(otheractivity.filename, 0);
    accountID = accountData.getString("accountID", null);
    accountPassword = accountData.getString("accountPassword", null);

    getActivity().getSupportLoaderManager().initLoader(0, null, this);
}

@Override
public Loader<ArrayList<Card>> onCreateLoader(int id, Bundle args) {
    return new NetworkTask(getActivity(), accountID, accountPassword, getString(R.string.login_url), getString(R.string.target_url));
}

@Override
public void onLoadFinished(Loader<ArrayList<Card>> loader, ArrayList<Card> result) {
    if (result != null) {
        CardArrayAdapter adapter = new CardArrayAdapter(getActivity(), result);
        CardListView cardListView = (CardListView) getActivity().findViewById(R.id.listView_schedule);
        if (cardListView != null) {
            cardListView.setAdapter(adapter);
        }
    } else {
        TextView warning = (TextView) getActivity().findViewById(R.id.textView_sheduleWarning);
        warning.setText("blah blah blah");
    }
}

@Override
public void onLoaderReset(Loader<ArrayList<Card>> loader) {
}

}

有什么想法是错的吗？也许与 PagerAdapter 或 CardArrayAdapter 有关？谢谢;)

Answer 1

有两种方法可以解决这个问题。

1. 将所有 fragment 加载在一起。用于此用途pager.setOffscreenPageLimit(numberOfFragments);将适配器设置为 vipager 后立即进行。

2. 删除从onCreate()到onCreateView()的代码当您在 viewpager 中滑动时，fragment 会重新加载并调用其 OncreateView() 。