Android Open Source - gnucash-android Database Cursor Loader

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License

The source code is released under:

Apache License

Java Source Code

/*
 * Copyright (c) 2012 - 2014 Ngewi Fet <ngewif@gmail.com>
 */*from w w  w. ja  v a2  s . c o m*/
 * 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.gnucash.android.db;

import android.content.Context;
import android.database.Cursor;
import android.support.v4.content.AsyncTaskLoader;

/**
 * Abstract base class for asynchronously loads records from a database and manages the cursor.
 * In order to use this class, you must subclass it and implement the
 * {@link #loadInBackground()} method to load the particular records from the database.
 * Ideally, the database has {@link DatabaseAdapter} which is used for managing access to the 
 * records from the database
 * @author Ngewi Fet <ngewif@gmail.com>
 * @see DatabaseAdapter
 */
public abstract class DatabaseCursorLoader extends AsyncTaskLoader<Cursor> {
  /**
   * Cursor which will hold the loaded data set.
   * The cursor will be returned from the {@link #loadInBackground()} method
   */
  private Cursor mCursor = null;
  
  /**
   * {@link DatabaseAdapter} which will be used to load the records from the database
   */
  protected DatabaseAdapter mDatabaseAdapter = null;
  
  /**
   * A content observer which monitors the cursor and provides notifications when
   * the dataset backing the cursor changes. You need to register the oberserver on
   * your cursor using {@link #registerContentObserver(Cursor)}
   */
  protected final ForceLoadContentObserver mObserver;
  
  /**
   * Constructor
   * Initializes the content observer
   * @param context Application context
   */
  public DatabaseCursorLoader(Context context) {
    super(context);
    mObserver = new ForceLoadContentObserver();
  }

  /**
   * Asynchronously loads the results from the database. 
   */
  public abstract Cursor loadInBackground();

  /**
   * Registers the content observer for the cursor. 
   * @param cursor {@link Cursor} whose content is to be observed for changes
   */
  protected void registerContentObserver(Cursor cursor){
    cursor.registerContentObserver(mObserver);
  }
  
  @Override
  public void deliverResult(Cursor data) {
    if (isReset()) {
      if (data != null) {
        onReleaseResources(data);
      }
      return;
    }

    Cursor oldCursor = mCursor;
    mCursor = data;

    if (isStarted()) {
      super.deliverResult(data);
    }

    if (oldCursor != null && oldCursor != data && !oldCursor.isClosed()) {
      onReleaseResources(oldCursor);
    }
  }

  @Override
  protected void onStartLoading() {
    if (mCursor != null){
      deliverResult(mCursor);
    }
        
        if (takeContentChanged() || mCursor == null) {
            // If the data has changed since the last time it was loaded
            // or is not currently available, start a load.
            forceLoad();
        }
  }
  
  @Override
  protected void onStopLoading() {
    cancelLoad();
  }
  
  @Override
  public void onCanceled(Cursor data) {
    super.onCanceled(data);
    onReleaseResources(data);
  }
  
  /**
     * Handles a request to completely reset the Loader.
     */
  @Override
  protected void onReset() {
    super.onReset();
    
    onStopLoading();

        // At this point we can release the resources associated with 'mCursor'
        // if needed.
        if (mCursor != null && !mCursor.isClosed()) {
            onReleaseResources(mCursor);           
        }  
        mCursor = null;
  }
  
  /**
     * Helper function to take care of releasing resources associated
     * with an actively loaded data set.
     * @param c {@link Cursor} to be released
     */
  protected void onReleaseResources(Cursor c) {
    if (c != null)
      c.close();    
    
    if (mDatabaseAdapter != null){
      mDatabaseAdapter.close();
    }
  }
}

Java Source Code List

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