org.uab.deic.uabdroid.loaders.DatabaseCursorLoader.java Source code

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Here is the source code for org.uab.deic.uabdroid.loaders.DatabaseCursorLoader.java

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/*
   Copyright 2012 Ruben Serrano, Joan Fuentes
    
   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at
    
   http://www.apache.org/licenses/LICENSE-2.0
    
   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
 */
package org.uab.deic.uabdroid.loaders;

import org.uab.deic.uabdroid.adapters.DatabaseAdapter;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.database.Cursor;
import android.support.v4.content.AsyncTaskLoader;

/**
 * 
 * @author Ruben Serrano
 *
 */
//As there is no Loader that enables us to load data asyncrhonously
//from a database, we must create a new one
public abstract class DatabaseCursorLoader extends AsyncTaskLoader<Cursor> {
    private DatabaseAdapter mDatabaseAdapter;
    private DatabaseReceiver mDatabaseReceiver;
    private String mEventToFilter;
    protected Cursor mCursor;

    // When constructed, we open the database
    public DatabaseCursorLoader(Context _context, String _eventToFilter) {
        super(_context);
        mDatabaseAdapter = new DatabaseAdapter(getContext());
        mDatabaseAdapter.openReadOnly();
        mEventToFilter = _eventToFilter;
    }

    protected DatabaseAdapter getDatabaseAdapter() {
        return mDatabaseAdapter;
    }

    // When the LoaderManager inits a load, we must call the
    // forceLoad() method from AsyncTaskLoader. Doing that, we 
    // are launching a new thread, that will execute the 
    // loadInBackground method
    @Override
    protected void onStartLoading() {
        // The DatabaseReceiver is used to capture the update database event.
        // BroadcastReceivers are a part of CursorLoader, but we will see them at
        // unit 5
        if (mDatabaseReceiver == null) {
            mDatabaseReceiver = new DatabaseReceiver();
        }

        forceLoad();
        super.onStartLoading();
    }

    // This method will be executed in a new thread
    // Here we perform the data loading operations
    @Override
    public Cursor loadInBackground() {
        // We only close the cursor in this method, and expect that the
        // class who inherits that one implements the query
        if ((mCursor != null) && (!mCursor.isClosed())) {
            mCursor.close();
            mCursor = null;
        }

        return placeQuery();
    }

    // To be implemented by each subclass with a call to the 
    // query that generates the cursor
    protected abstract Cursor placeQuery();

    // If the loader if reseted, we must do some cleaning :)
    @Override
    protected void onReset() {
        super.onReset();

        // Stop the loading, if it's being performed
        onStopLoading();

        // Close the cursor if it's opened
        if ((mCursor != null) && (!mCursor.isClosed())) {
            mCursor.close();
            mCursor = null;
        }

        // Close the database
        if (mDatabaseAdapter != null) {
            mDatabaseAdapter.close();
            mDatabaseAdapter = null;
        }

        // Unregister the receiver
        if (mDatabaseReceiver != null) {
            getContext().unregisterReceiver(mDatabaseReceiver);
            mDatabaseReceiver = null;
        }
    }

    @Override
    public void onCanceled(Cursor _data) {
        super.onCanceled(_data);

        // Close the cursor if it's opened
        if ((mCursor != null) && (!mCursor.isClosed())) {
            mCursor.close();
            mCursor = null;
        }
    }

    private class DatabaseReceiver extends BroadcastReceiver {
        public DatabaseReceiver() {
            // We need to register the receiver to filter one or more intents
            IntentFilter filter = new IntentFilter(mEventToFilter);
            getContext().registerReceiver(this, filter);
        }

        @Override
        public void onReceive(Context _context, Intent _intent) {
            if (_intent.getAction().compareTo(mEventToFilter) == 0) {
                // We call onContentChanged(), a method from the Loader, to indicate
                // that a change in the database has taken place, so the Loader has
                // to restart the loading process
                onContentChanged();
            }
        }
    }
}