ContentResolverTemplate.java :  » Widget » android-recent-widget » org » recentwidget » dao » Android Open Source

package org.recentwidget.dao;

import java.util.List;

import org.recentwidget.EventListBuilder;
import org.recentwidget.model.RecentContact;

import android.content.ContentResolver;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.database.Cursor;
import android.net.Uri;
import android.preference.PreferenceManager;
import android.util.Log;

public abstract class ContentResolverTemplate implements EventObserver {

  private static final String TAG = "RW:ContentResolverTplt";

  protected String[] projection;

  protected String sortOrder;

  protected Context context;

  private ContentResolver contentResolver;

  protected abstract long extractEvent(EventListBuilder builder, Cursor cursor);

  protected abstract int getTargetType();

  protected String preferenceEnabledName = null;

  // as a getter because we want to override it
  protected abstract Uri getContentUri();

  @Override
  public List<RecentContact> update(List<RecentContact> recentContacts,
      Intent intent, Context context) {

    if (intent != null) {
      Log.d(TAG, "Received broadcasted " + intent.getAction());
    }

    // Note: Not concurrent-friendly!

    // Note: Make sure no unnecessary ArrayLists created in all those
    // params/returns.

    // Check with Preference first

    SharedPreferences prefs = PreferenceManager
        .getDefaultSharedPreferences(context);

    if (preferenceEnabledName == null
        || prefs.getBoolean(preferenceEnabledName, false)) {

      this.context = context;
      this.contentResolver = context.getContentResolver();

      return fetchEvents(recentContacts);

    } else {
      // Do nothing
      return recentContacts;
    }

  }

  /**
   * Only one-time use as the template's content resolver is set to null
   * afterwards. (this is to avoid any long-lived reference / leaks)
   * 
   * Uses the specific Dao extractEvent to traverse (pattern?) the cursor.
   * 
   */
  protected List<RecentContact> fetchEvents(List<RecentContact> recentContacts) {

    // The builder is useful in order for the business logic to be stored
    // elsewhere.

    EventListBuilder builder = new EventListBuilder(context, recentContacts);

    Cursor cursor = null;

    try {

      // Do not use managedQuery() because we will unload it ourselves

      cursor = contentResolver.query(getContentUri(), projection,
          getQuery(), getQueryArgs(), sortOrder);

      if (cursor.moveToFirst()) {

        while (!cursor.isAfterLast()) {

          // "extract" actually adds to the list

          long eventDate = extractEvent(builder, cursor);

          // At this point, the event was already added. Just check if
          // next event should be fetched; or do we have enough events
          // already.

          if (builder.isFull(eventDate, getTargetType())) {
            break;
          }

          cursor.moveToNext();
        }
      }

    } catch (Exception e) {
      // Let exception escape, so we have a functioning widget
      Log.e(TAG, "Exception while querying " + getContentUri(), e);
    } finally {
      if (cursor != null) {
        cursor.close();
      }
    }

    // Avoid memory leaks
    // http://www.curious-creature.org/2008/12/18/avoid-memory-leaks-on-android/

    contentResolver = null;
    context = null;

    return builder.build();
  }

  protected String[] getQueryArgs() {
    return null;
  }

  protected String getQuery() {
    return null;
  }

}