方向更改时未调用 onCreateLoader

Question

我的问题和这个基本一样：Sometimes don't get onCreateLoader callback after calling initLoader

我有 2 个 ListFragments 包含在 ViewPager 中。一开始它们加载正常，但是当我改变方向时，initLoader方法不会调用onCreateLoader。 但是，如果我恢复到最初的方向，一切都会好起来的。

这是我的FragmentActivity 代码：

import java.util.Locale;

import com.d.camera.R;
import com.d.camera.R.id;
import com.d.camera.R.layout;
import com.d.camera.R.menu;
import com.d.camera.R.string;

import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.NavUtils;
import android.support.v4.view.ViewPager;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class HistoryFragments 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;

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

    // Set up the action bar.
    final ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    actionBar.setDisplayShowTitleEnabled(false);
    actionBar.setDisplayShowHomeEnabled(false);

    // 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 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));
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.history, menu);
    return true;
}

@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) {
}

/**
 * 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 DummySectionFragment (defined as a static inner class
        // below) with the page number as its lone argument.

        Fragment fragment = null;

        if (position == 0) {
            fragment = new HistoryListFragment();               
        } else{
            fragment = new HistoryElemListFragment();

        }
        return fragment;
    }

    @Override
    public int getCount() {
        // Show 2 total pages.
        return 2;
    }

    @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);
        }
        return null;
    }
}


}

这是ListFragments 之一的代码：

import java.io.File;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

import com.d.camera.HistoryContentProvider;
import com.d.camera.HistoryDatabase;
import com.d.camera.HistoryEntry;
import com.d.camera.R;

import android.app.LoaderManager;
import android.content.Context;
import android.content.CursorLoader;
import android.content.Intent;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.util.Log;
import android.view.ContextMenu;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.ViewGroup;
import android.widget.FilterQueryProvider;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.TextView;
import android.widget.AdapterView.AdapterContextMenuInfo;
import android.widget.SimpleCursorAdapter.ViewBinder;

public class HistoryListFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor>{

    private static final int LOADER_ID = 0x01;
    private static final int DELETE_ID = Menu.FIRST + 1;
    public static final String SECTION_NUMBER = "section_number";
    private SimpleCursorAdapter adapter;
    private Context context;

    public HistoryListFragment() {
    }


    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        context = getActivity();
        fillData();
        registerForContextMenu(getListView());
    }

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




    private void fillData() {
        getActivity().getLoaderManager().initLoader(LOADER_ID, null, this);
        String[] from = new String[] {
                HistoryDatabase.MOBILE_RESULT,
                HistoryDatabase.FP_TIMESTAMP,
                HistoryDatabase.PRODUCT_IMAGE,};

        int[] to = new int[] {
                R.id.resultImage,
                R.id.time,
                R.id.productImage,};

        adapter = new SimpleCursorAdapter(context, R.layout.history_element, null, from, to, 0);


        // We want monitor the list setup and change the milliseconds time to a readable format.*******
        adapter.setViewBinder(new ViewBinder(){
            public boolean setViewValue(View v, Cursor c, int columnIndex) {

                if(columnIndex == c.getColumnIndex(HistoryDatabase.FP_TIMESTAMP))
                {
                    Long timeInMilli = c.getLong(c.getColumnIndex(HistoryDatabase.FP_TIMESTAMP));
                    SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM dd HH:mm:ss z yyyy", Locale.ENGLISH);
                    String formatedTime = sdf.format(new Date(timeInMilli));
                    TextView tv = (TextView)v;
                    tv.setText(formatedTime);
                    return true;
                }
                return false;
            }
        });
        //*********************************************************************************************

        setListAdapter(adapter);

  }


    @Override
    public void onCreateContextMenu(ContextMenu menu, View v,
            ContextMenuInfo menuInfo) {
        super.onCreateContextMenu(menu, v, menuInfo);
        menu.add(0, DELETE_ID, 0, R.string.menu_delete);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        //...
        return super.onContextItemSelected(item);
    }



    // Reaction to the menu selection
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        //...
        return super.onOptionsItemSelected(item);
    }


    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        String[] projection = new String[]{HistoryDatabase.ID, HistoryDatabase.MOBILE_RESULT, HistoryDatabase.MOBILE_SCORE, HistoryDatabase.FP_TIMESTAMP, HistoryDatabase.PRODUCT_IMAGE, HistoryDatabase.QR_MESSAGE};
        return new CursorLoader(context, HistoryContentProvider.CONTENT_URI, projection, null, null, HistoryDatabase.ID + " DESC");
    }

    @Override
    public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) {
        adapter.swapCursor(cursor);     
    }

    @Override
    public void onLoaderReset(Loader<Cursor> cursorLoader) {
        adapter.swapCursor(null);           
    }   

    public void onListItemClick(ListView l, View v, int position, long id) {
        //do something
    }
}

我尝试了这些方法的不同组合destroyLoader,restartLoader，但没有任何成功...有人知道发生了什么吗？

编辑 使用LoaderManager.enableDebugLogging(true) 我得到以下日志： 第一次加载给出了这个

 initLoader in LoaderManager{424a7950 in HistoryFragments{42507c68}}: args=null
   Starting: LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}
   Created new loader LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}
 initLoader in LoaderManager{424a7950 in HistoryFragments{42507c68}}: args=null
   Starting: LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
   Created new loader LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
 onLoadComplete: LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}
   onLoadFinished in CursorLoader{42faae18 id=1}: CursorWrapperInner{42506d58}
 onLoadComplete: LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
   onLoadFinished in CursorLoader{42e5a2f8 id=2}: CursorWrapperInner{42fab1f0}

然后当我改变方向时，它会给出这个

Retaining in LoaderManager{424a7950 in HistoryFragments{42507c68}}
   Retaining: LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
   Retaining: LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}
 Destroying Inactive in LoaderManager{424a7950 in HistoryFragments{42507c68}}
 initLoader in LoaderManager{424a7950 in HistoryFragments{426d0af0}}: args=null
   Re-using existing loader LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}
 initLoader in LoaderManager{424a7950 in HistoryFragments{426d0af0}}: args=null
   Re-using existing loader LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
 Finished Retaining in LoaderManager{424a7950 in HistoryFragments{426d0af0}}
   Finished Retaining: LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
   Stopping: LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
   Finished Retaining: LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}
   Stopping: LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}

然后当我回到初始方向时，我收到一个错误，然后一切都重新加载：

Retaining in LoaderManager{424a7950 in HistoryFragments{426d0af0}}
 Called doRetain when not started: LoaderManager{424a7950 in HistoryFragments{426d0af0}}
 java.lang.RuntimeException: here
    at android.app.LoaderManagerImpl.doRetain(LoaderManager.java:795)
    at android.app.Activity.performStop(Activity.java:5497)
    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3591)
    at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3654)
    at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3854)
    at android.app.ActivityThread.access$800(ActivityThread.java:159)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1322)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:176)
    at android.app.ActivityThread.main(ActivityThread.java:5419)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:525)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
    at dalvik.system.NativeStart.main(Native Method)
 Destroying Active in LoaderManager{424a7950 in HistoryFragments{426d0af0}}
   Destroying: LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
   Reseting: LoaderInfo{42e5a280 #2 : CursorLoader{42e5a2f8}}
   Destroying: LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}
   Reseting: LoaderInfo{424a7da0 #1 : CursorLoader{42faae18}}
 Destroying Inactive in LoaderManager{424a7950 in HistoryFragments{426d0af0}}
 Destroying Active in LoaderManager{424a7950 in HistoryFragments{426d0af0}}
 Destroying Inactive in LoaderManager{424a7950 in HistoryFragments{426d0af0}}
 initLoader in LoaderManager{4271b070 in HistoryFragments{42702c68}}: args=null
   Starting: LoaderInfo{4271b690 #1 : CursorLoader{4271b708}}
   Created new loader LoaderInfo{4271b690 #1 : CursorLoader{4271b708}}
 initLoader in LoaderManager{4271b070 in HistoryFragments{42702c68}}: args=null
   Starting: LoaderInfo{42720ab8 #2 : CursorLoader{42720b30}}
   Created new loader LoaderInfo{42720ab8 #2 : CursorLoader{42720b30}}
 onLoadComplete: LoaderInfo{4271b690 #1 : CursorLoader{4271b708}}
   onLoadFinished in CursorLoader{4271b708 id=1}: CursorWrapperInner{4271f518}
 onLoadComplete: LoaderInfo{42720ab8 #2 : CursorLoader{42720b30}}
   onLoadFinished in CursorLoader{42720b30 id=2}: CursorWrapperInner{427222c0}

然后日志会重复自身以进一步改变方向。为什么CursorLoaders 被停止而不是重新启动？如何重新启动它们？

编辑 2

感谢 nikis，我解决了我的问题，但他提出了一个有趣的问题： 为什么android.app.LoaderManager 不起作用？

这是使用支持版本后的日志。 第一次加载的结果与上面相同，但在方向改变后，重新使用光标不会停止它们。

 Retaining in LoaderManager{43945c70 in HistoryFragments{427cb468}}
   Retaining: LoaderInfo{439d8a58 #2 : CursorLoader{439d8ad0}}
   Retaining: LoaderInfo{432dea88 #1 : CursorLoader{4393ad48}}
 Destroying Inactive in LoaderManager{43945c70 in HistoryFragments{427cb468}}
 initLoader in LoaderManager{43945c70 in HistoryFragments{438f0a38}}: args=null
   Re-using existing loader LoaderInfo{432dea88 #1 : CursorLoader{4393ad48}}
 initLoader in LoaderManager{43945c70 in HistoryFragments{438f0a38}}: args=null
   Re-using existing loader LoaderInfo{439d8a58 #2 : CursorLoader{439d8ad0}}
 Starting in LoaderManager{43945c70 in HistoryFragments{438f0a38}}
 Finished Retaining in LoaderManager{43945c70 in HistoryFragments{438f0a38}}
   Finished Retaining: LoaderInfo{439d8a58 #2 : CursorLoader{439d8ad0}}
   onLoadFinished in CursorLoader{439d8ad0 id=2}: CursorWrapperInner{43952be0}
   Finished Retaining: LoaderInfo{432dea88 #1 : CursorLoader{4393ad48}}
   onLoadFinished in CursorLoader{4393ad48 id=1}: CursorWrapperInner{43952fa8}

当我回到最初的方向时，结果是这样的：

Retaining in LoaderManager{43945c70 in HistoryFragments{438f0a38}}
   Retaining: LoaderInfo{439d8a58 #2 : CursorLoader{439d8ad0}}
   Retaining: LoaderInfo{432dea88 #1 : CursorLoader{4393ad48}}
 Destroying Inactive in LoaderManager{43945c70 in HistoryFragments{438f0a38}}
 initLoader in LoaderManager{43945c70 in HistoryFragments{432cab50}}: args=null
   Re-using existing loader LoaderInfo{432dea88 #1 : CursorLoader{4393ad48}}
 initLoader in LoaderManager{43945c70 in HistoryFragments{432cab50}}: args=null
   Re-using existing loader LoaderInfo{439d8a58 #2 : CursorLoader{439d8ad0}}
 Starting in LoaderManager{43945c70 in HistoryFragments{432cab50}}
 Finished Retaining in LoaderManager{43945c70 in HistoryFragments{432cab50}}
   Finished Retaining: LoaderInfo{439d8a58 #2 : CursorLoader{439d8ad0}}
   onLoadFinished in CursorLoader{439d8ad0 id=2}: CursorWrapperInner{43952be0}
   Finished Retaining: LoaderInfo{432dea88 #1 : CursorLoader{4393ad48}}
   onLoadFinished in CursorLoader{4393ad48 id=1}: CursorWrapperInner{43952fa8}

Answer 1

您可以使用LoaderManager.enableDebugLogging(true) 来调试您的加载程序行为，或者您可以尝试使用getSupportLoadermanager() 而不是getLoaderManager()

Answer 2

当您将支持库中的一些活动与 android.app.LoaderManager 结合使用时，似乎会出现此问题。

我在使用 android.support.v7.app.ActionBarActivity 和 android.app.LoaderManager 时遇到了完全相同的问题：

• 初始加载工作
• 然后当方向改变时，加载器更新完成
• 然后当回到原来的方向时，它又可以工作了。

通过改用 android.support.v4.app.LoaderManager，一切又开始完美运行！

Answer 3

我遇到了与 OP 相同的问题，因为在配置更改后没有调用 onCreateLoader。然而，这并不是真正的问题（因为使用getSupportLoaderManager().enableDebugLogging(true); 表明我的加载器已成功重复使用，因此无需重新创建新的加载器）。

所以我查看了我的onLoadFinished(Loader<Cursor> loader, Cursor cursor) 方法，发现与onCreateLoader 不同，它总是在配置更改后调用。并且每次都会填充cursor。 :-)

问题是光标的位置在结果集的end，所以我尝试迭代它没有导致任何操作（因此，我的 UI 没有被填充）。

有效的解决方案是将光标位置移到第一个之前：

// Move cursor before first so we can still iterate after config change
cursor.moveToPosition(-1);

我把它放在我的 onLoadFinished 方法的开头。

Answer 4

关于您引用的问题，有一个解决方法记录在案。在 onResume 中调用 restartLoader 而不是在其他地方创建加载器。如果需要，restartLoader 会创建。