android - 来自光标加载器的 ListFragment 无法在方向更改时显示任何内容

Question

我正在开发一个使用 ActionBarSherlock 和 ViewPagerIndicator 构建的 Android 应用程序使用 Android 兼容性库的 minSDK 为 8 (Android 2.2) 和 targetSDK 为 16 (Android 4.1)。我有应用程序的消息传递部分，消息存储在 SQLite 数据库中，我使用的是 CommonsWare 的 cwac-loaderex。在 SQLite 数据库中使用游标加载器。当 Activity 加载时，一切正常并显示消息，但当我旋转设备时，它只显示一个带有加载循环的 ListFragment。

打开 LoaderManager.enableDebugLogging(true) 现有加载器在我旋转时被重用，我还在 onDestroy 中尝试了 getSupportLoaderManager().destroyLoader(ID) 并且正在创建新的加载器，但我仍然有相同的结果，一个 ListFragment 与加载圈。在打开消息传递 Activity 之前，我已经在两个方向上进行了测试，它们都工作正常，这只是当我在消息传递 Activity 可见时旋转时的一个问题。我还尝试以纵向方式进入消息传递 Activity ，单击一条消息将我带到另一个 Activity 而不会破坏消息传递 Activity ，更改为横向，然后按回消息传递 Activity ，一切都显示正常。

我无法弄清楚为什么消息在旋转后没有显示。如果有任何想法或帮助，我将不胜感激。我在下面包含了我的消息传递 Activity 。

import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.ListFragment;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.Loader;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.SimpleCursorAdapter;

import com.actionbarsherlock.app.SherlockFragmentActivity;
import com.actionbarsherlock.view.Menu;
import com.actionbarsherlock.view.MenuItem;
import com.commonsware.cwac.loaderex.acl.SQLiteCursorLoader;
import com.viewpagerindicator.TitlePageIndicator;

import com.lukekorth.DB.DatabaseHelper;
import com.lukekorth.Helpers.MessageFragment;

public class MyMessagesActivity extends SherlockFragmentActivity implements
LoaderManager.LoaderCallbacks<Cursor> {

        private FragmentAdapter mFragmentAdapter;
    private ViewPager mPager;
    private DatabaseHelper mDB;
    private SimpleCursorAdapter mInboxCursorAdapter;
    private SimpleCursorAdapter mArchiveCursorAdapter;

    private MessageFragment[] content = new MessageFragment[2];

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.messages);

        getSupportActionBar().setHomeButtonEnabled(true);
        getSherlock().getActionBar().setDisplayHomeAsUpEnabled(true);

        mDB = new DatabaseHelper(this);

        content[0] = new MessageFragment();
        content[1] = new MessageFragment();

        /////////--------------------///////
        LoaderManager.enableDebugLogging(true);

        mInboxCursorAdapter = new SimpleCursorAdapter(this, R.layout.message_item, null, new String[] { DatabaseHelper.senderName,
                DatabaseHelper.lastUpdate, DatabaseHelper.subject, DatabaseHelper.lastSnippet }, new int[] { R.id.name, R.id.date,
                R.id.subject, R.id.snippet });

        mArchiveCursorAdapter = new SimpleCursorAdapter(this, R.layout.message_item, null, new String[] { DatabaseHelper.senderName,
                DatabaseHelper.lastUpdate, DatabaseHelper.subject, DatabaseHelper.lastSnippet }, new int[] { R.id.name, R.id.date,
                R.id.subject, R.id.snippet });

        content[0].setListAdapter(mInboxCursorAdapter);
        content[1].setListAdapter(mArchiveCursorAdapter);

        getSupportLoaderManager().initLoader(0, null, this);
        getSupportLoaderManager().initLoader(1, null, this);
        ///////////////------------------////////////

        mFragmentAdapter = new FragmentAdapter(getSupportFragmentManager());
        mFragmentAdapter.updateContent(content);

        mPager = (ViewPager) findViewById(R.id.pager);
        mPager.setAdapter(mFragmentAdapter);

        TitlePageIndicator indicator = (TitlePageIndicator) findViewById(R.id.indicator);
        indicator.setViewPager(mPager);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();

        getSupportLoaderManager().destroyLoader(0);
        getSupportLoaderManager().destroyLoader(1);

        mDB.close();
    }

    @Override
    public Loader<Cursor> onCreateLoader(int folder, Bundle arg1) {
        String query = "select " + DatabaseHelper.threads + "." + DatabaseHelper.threadKey + "," + DatabaseHelper.subject +
                "," + DatabaseHelper.archive + "," + DatabaseHelper.otherUser + "," + DatabaseHelper.lastUpdate + "," +
                DatabaseHelper.lastSnippet + "," + DatabaseHelper.senderPicture + "," + DatabaseHelper.senderName + " from " +
                DatabaseHelper.threads + " left join " + DatabaseHelper.senders + " on " + DatabaseHelper.threads + "." +
                DatabaseHelper.otherUser + " = " + DatabaseHelper.senders + "." + DatabaseHelper.senderKey + " where " +
                DatabaseHelper.archive;

        if(folder == 0)
            query += " = 0 order by ";
        else
            query += " = 1 order by ";

        query += DatabaseHelper.lastUpdate + " desc";

        return new SQLiteCursorLoader(this, mDB, query, null);
    }

    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
        if(loader.getId() == 0)
            mInboxCursorAdapter.swapCursor(cursor);
        else
            mArchiveCursorAdapter.swapCursor(cursor);
    }

    @Override
    public void onLoaderReset(Loader<Cursor> loader) {
        if(loader.getId() == 0)
            mInboxCursorAdapter.swapCursor(null);
        else
            mArchiveCursorAdapter.swapCursor(null);
    }
}

class FragmentAdapter extends FragmentPagerAdapter {
    protected static final String[] TITLE = new String[] { "Inbox", "Archive", };

    private ListFragment[] mContent;

    private int mCount = TITLE.length;

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

    public void updateContent(MessageFragment[] content){
        mContent = content;
    }

    @Override
    public Fragment getItem(int position) {
        return mContent[position % mContent.length];
    }

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

    @Override
    public CharSequence getPageTitle(int position) {
        return FragmentAdapter.TITLE[position % TITLE.length];
    }
}

Answer 1

事实证明，ViewPager 和 fragment 标签有些奇怪。我的解决方案是在 onSaveInstanceState() 中的事务中添加 fragment ，然后在 onCreate()(第二段代码)中使用生成的标签按标签获取 fragment 在 ViewPager 中。我能够从 this question 中找出使用的标签方案.希望这可以为某人节省几天的工作。

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    FragmentManager fm = getSupportFragmentManager();
    FragmentTransaction ft = fm.beginTransaction();

    ft.add(content[0], content[0].getTag());
    ft.add(content[1], content[1].getTag());

    ft.commit();
}




    FragmentManager fm = getSupportFragmentManager();

    content[0] = (MessageFragment) fm.findFragmentByTag("android:switcher:"+ R.id.pager + ":0");
    content[1] = (MessageFragment) fm.findFragmentByTag("android:switcher:"+ R.id.pager + ":1");

    if(content[0] == null || content[1] == null){
        content[0] = new MessageFragment();
        content[1] = new MessageFragment();

        content[0].setListAdapter(mInboxCursorAdapter);
        content[1].setListAdapter(mArchiveCursorAdapter);
    }