SupportListLoader.java

/*
 * Copyright 2013 Telly Inc.
 *
 * 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 com.telly.groundy.loader;

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

import java.util.List;

/**
 * AsyncTaskLoader which handles lists of generic objects
 *
 * @author Cristian Castiblanco <cristian@elhacker.net>
 */
public abstract class SupportListLoader<T> extends AsyncTaskLoader<List<T>> {
  private List<T> mList;

  public SupportListLoader(Context context) {
    super(context);
  }

  /* Runs on a worker thread */
  @Override
  public List<T> loadInBackground() {
    return getData();
  }

  /* Runs on the UI thread */
  @Override
  public void deliverResult(List<T> list) {
    if (isReset()) {
      // An async query came in while the loader is stopped
      if (list != null) {
        list.clear();
      }
      return;
    }
    List<T> oldList = mList;
    mList = list;

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

    if (oldList != null && oldList != list && oldList.size() > 0) {
      oldList.clear();
    }
  }

  /**
   * Starts an asynchronous load of the contacts list data. When the result is ready the callbacks
   * will be called on the UI thread. If a previous load has been completed and is still valid
   * the result may be passed to the callbacks immediately.
   * <p/>
   * Must be called from the UI thread
   */
  @Override
  protected void onStartLoading() {
    if (mList != null) {
      deliverResult(mList);
    }
    if (takeContentChanged() || mList == null) {
      forceLoad();
    }
  }

  /**
   * Must be called from the UI thread
   */
  @Override
  protected void onStopLoading() {
    // Attempt to cancel the current load task if possible.
    cancelLoad();
  }

  @Override
  public void onCanceled(List<T> list) {
    if (list != null && list.size() > 0) {
      list.clear();
    }
  }

  @Override
  protected void onReset() {
    super.onReset();

    // Ensure the loader is stopped
    onStopLoading();

    if (mList != null && mList.size() > 0) {
      mList.clear();
    }
    mList = null;
  }

  protected List<T> getList() {
    return mList;
  }

  /**
   * @return a List with the data to load
   */
  protected abstract List<T> getData();
}