Android - onLoadFinished not called

问题:

I am facing an issue with Loader.

I have an Activity, which displays list of records retrieved from local DB. When the activity starts, records are automatically loaded via LoaderManager.initLoader() method.

There is also possibility to manually refresh the list via refresh button in ActionBarSherlock. However, after finishing another activity which adds a record to DB, onLoadFinished is not called.

I am using SimpleCursorLoader and here is code snippet from the activity:

@Override
public void onStart() {
   ...
   getSupportLoaderManager().initLoader(0, null, this);
}

@Override
public void onPause() {
   ...
   getSupportLoaderManager().destroyLoader(0);
}

public void refreshRecords() {
   getSupportLoaderManager().restartLoader(0, null, this);
}

@Override
public Loader<Cursor> onCreateLoader(int id, final Bundle args) {
Loader<Cursor> l = new SimpleCursorLoader(this) {
    @Override
    public Cursor loadInBackground() {
        return recordDAO.getCursor();
    }
};
l.forceLoad();
return l;
}

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor c) {
   // updateUI
}

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

The issue is that after finishing the other activity, onLoaderCreate is called, but onLoaderFinished is not called.

after some debugging, I've found that SimpleCursorAdapter.deliverResults() is also called, bud ends up on .. if (isReset()) { ..

Am I missing something? How to force the reload of data?

Thank you in advance

回答1:

I have finally found the solution to this problem thanks to the discussion on

https://groups.google.com/forum/#!topic/android-developers/DbKL6PVyhLI

public static <T> void initLoader(final int loaderId, final Bundle args, final LoaderCallbacks<T> callbacks,
        final LoaderManager loaderManager) {
    final Loader<T> loader = loaderManager.getLoader(loaderId);
    if (loader != null && loader.isReset()) {
        loaderManager.restartLoader(loaderId, args, callbacks);
    } else {
        loaderManager.initLoader(loaderId, args, callbacks);
    }
}

In addition as of support library 28 make sure that you don't call initLoader from within Fragment.onCreate(). As the updated documentation states

You typically initialize a Loader within the activity's onCreate() method, or within the fragment's onActivityCreated() method.

see https://developer.android.com/guide/components/loaders

回答2:

RaB solution dont work for me

My worked Solution, was always destroy Loader before restart

Loader<Cursor> loader = mLoaderManager.getLoader(mKeyLoader);
if (loader != null)
{
    mLoaderManager.destroyLoader(mKeyLoader);
}
mLoaderManager.restartLoader(mKeyLoader, args, this);

回答3:

In addition to RaB's answer, if you are using a custom Loader, make sure that if you call super if you overwrite deliverResult():

@Override
public void deliverResult(D data) {
    super.deliverResult(data); // <--onLoadFinished() will not be called if you don't call this
    ...
}

回答4:

fwiw, I had a similar problem from attempting to immediately restart the loader a second time, before the first onLoadFinished was called, resulting in neither being called.

this worked for me:

if( loader == null )
    loader = loaderMngr.initLoader(
        0, null, myLoaderCallbacks
        ); 
else if( loader.isAbandoned() )
    return;
else
    loaderMngr.restartLoader(
        0, null, myLoaderCallbacks
        );    

回答5:

Check the support library.Use this import android.support.v4.app. Don't use android.app.loadermanager.

import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;

Initialize part

    LoaderManager mLoaderManager=getSupportLoaderManager(); 

      LoaderManager.LoaderCallbacks<Cursor> mCursorLoaderCallbacks=new LoaderManager.LoaderCallbacks<Cursor>() {
                @Override
                public Loader<Cursor> onCreateLoader(int id, Bundle cursor) {
                      return new CursorLoader(getActivity(), MediaStore.Video.Media.EXTERNAL_CONTENT_URI, COLUMNS_OF_INTEREST, null, null,
                            MediaStore.Video.Media.DATE_ADDED + " DESC");
                }
                @Override
                public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
                }


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

  mLoaderManager.initLoader(URL_LOADER_EXTERNAL, null, mCursorLoaderCallbacks);