Added documentation to DBWriter

4 files changed, 647 insertions, 504 deletions

diff --git a/src/de/danoeh/antennapod/service/PlaybackService.java b/src/de/danoeh/antennapod/service/PlaybackService.java
index a173dfdfb..63a4d0471 100644
--- a/src/de/danoeh/antennapod/service/PlaybackService.java
+++ b/src/de/danoeh/antennapod/service/PlaybackService.java
@@ -775,7 +775,6 @@ public class PlaybackService extends Service {
 
         if (media instanceof FeedMedia) {
             FeedItem item = ((FeedMedia) media).getItem();
-            ((FeedMedia) media).setPlaybackCompletionDate(new Date());
             DBWriter.markItemRead(PlaybackService.this, item, true, true);
             nextItem = DBTasks.getQueueSuccessorOfItem(this, item.getId(), queue);
             isInQueue = media instanceof FeedMedia
@@ -783,7 +782,7 @@ public class PlaybackService extends Service {
             if (isInQueue) {
                 DBWriter.removeQueueItem(PlaybackService.this, item.getId(), true);
             }
-            DBWriter.addItemToPlaybackHistory(PlaybackService.this, item);
+            DBWriter.addItemToPlaybackHistory(PlaybackService.this, (FeedMedia) media);
             DBWriter.setFeedMedia(PlaybackService.this, (FeedMedia) media);
             long autoDeleteMediaId = ((FeedComponent) media).getId();
             if (shouldStream) {
diff --git a/src/de/danoeh/antennapod/storage/DBReader.java b/src/de/danoeh/antennapod/storage/DBReader.java
index 71d11f13b..b1ebbc45d 100644
--- a/src/de/danoeh/antennapod/storage/DBReader.java
+++ b/src/de/danoeh/antennapod/storage/DBReader.java
@@ -27,6 +27,8 @@ import de.danoeh.antennapod.util.comparator.FeedItemPubdateComparator;
  * Provides methods for reading data from the AntennaPod database.
  * In general, all database calls in DBReader-methods are executed on the caller's thread.
  * This means that the caller should make sure that DBReader-methods are not executed on the GUI-thread.
+ * This class will use the {@link de.danoeh.antennapod.feed.EventDistributor} to notify listeners about changes in the database.
+
  */
 public final class DBReader {
     private static final String TAG = "DBReader";
diff --git a/src/de/danoeh/antennapod/storage/DBWriter.java b/src/de/danoeh/antennapod/storage/DBWriter.java
index 3db0b8a33..4ad9e9e1f 100644
--- a/src/de/danoeh/antennapod/storage/DBWriter.java
+++ b/src/de/danoeh/antennapod/storage/DBWriter.java
@@ -1,7 +1,7 @@
 package de.danoeh.antennapod.storage;
 
 import java.io.File;
-import java.util.Collections;
+import java.util.Date;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.concurrent.ExecutorService;
@@ -22,517 +22,645 @@ import de.danoeh.antennapod.service.PlaybackService;
 import de.danoeh.antennapod.service.download.DownloadStatus;
 import de.danoeh.antennapod.util.QueueAccess;
 
+/**
+ * Provides methods for writing data to AntennaPod's database.
+ * In general, DBWriter-methods will be executed on an internal ExecutorService.
+ * Some methods return a Future-object which the caller can use for waiting for the method's completion. The returned Future's
+ * will NOT contain any results.
+ * The caller can also use the {@link EventDistributor} in order to be notified about the method's completion asynchronously.
+ * This class will use the {@link EventDistributor} to notify listeners about changes in the database.
+ */
 public class DBWriter {
-	private static final String TAG = "DBWriter";
-
-	private static final ExecutorService dbExec;
-	static {
-		dbExec = Executors.newSingleThreadExecutor(new ThreadFactory() {
-
-			@Override
-			public Thread newThread(Runnable r) {
-				Thread t = new Thread(r);
-				t.setPriority(Thread.MIN_PRIORITY);
-				return t;
-			}
-		});
-	}
-
-	private DBWriter() {
-	}
-
-	public static void deleteFeedMediaOfItem(final Context context,
-			final long itemId) {
-		dbExec.submit(new Runnable() {
-			@Override
-			public void run() {
-				final FeedItem item = DBReader.getFeedItem(context, itemId);
-				if (item != null && item.hasMedia()) {
-					final FeedMedia media = item.getMedia();
-					boolean result = false;
-					if (media.isDownloaded()) {
-						// delete downloaded media file
-						File mediaFile = new File(media.getFile_url());
-						if (mediaFile.exists()) {
-							result = mediaFile.delete();
-						}
-						media.setDownloaded(false);
-						media.setFile_url(null);
-						setFeedMedia(context, media);
-
-						// If media is currently being played, change playback
-						// type to 'stream' and shutdown playback service
-						SharedPreferences prefs = PreferenceManager
-								.getDefaultSharedPreferences(context);
-						if (PlaybackPreferences.getCurrentlyPlayingMedia() == FeedMedia.PLAYABLE_TYPE_FEEDMEDIA) {
-							if (media.getId() == PlaybackPreferences
-									.getCurrentlyPlayingFeedMediaId()) {
-								SharedPreferences.Editor editor = prefs.edit();
-								editor.putBoolean(
-										PlaybackPreferences.PREF_CURRENT_EPISODE_IS_STREAM,
-										true);
-								editor.commit();
-							}
-							if (PlaybackPreferences
-									.getCurrentlyPlayingFeedMediaId() == media
-									.getId()) {
-								context.sendBroadcast(new Intent(
-										PlaybackService.ACTION_SHUTDOWN_PLAYBACK_SERVICE));
-							}
-						}
-					}
-					if (AppConfig.DEBUG)
-						Log.d(TAG, "Deleting File. Result: " + result);
-				}
-			}
-		});
-	}
-
-	public static Future<?> deleteFeed(final Context context, final long feedId) {
-		return dbExec.submit(new Runnable() {
-			@Override
-			public void run() {
-				DownloadRequester requester = DownloadRequester.getInstance();
-				SharedPreferences prefs = PreferenceManager
-						.getDefaultSharedPreferences(context
-								.getApplicationContext());
-				final Feed feed = DBReader.getFeed(context, feedId);
-				if (feed != null) {
-					if (PlaybackPreferences.getCurrentlyPlayingMedia() == FeedMedia.PLAYABLE_TYPE_FEEDMEDIA
-							&& PlaybackPreferences.getLastPlayedFeedId() == feed
-									.getId()) {
-						context.sendBroadcast(new Intent(
-								PlaybackService.ACTION_SHUTDOWN_PLAYBACK_SERVICE));
-						SharedPreferences.Editor editor = prefs.edit();
-						editor.putLong(
-								PlaybackPreferences.PREF_CURRENTLY_PLAYING_FEED_ID,
-								-1);
-						editor.commit();
-					}
-
-					PodDBAdapter adapter = new PodDBAdapter(context);
-					adapter.open();
-					// delete image file
-					if (feed.getImage() != null) {
-						if (feed.getImage().isDownloaded()
-								&& feed.getImage().getFile_url() != null) {
-							File imageFile = new File(feed.getImage()
-									.getFile_url());
-							imageFile.delete();
-						} else if (requester.isDownloadingFile(feed.getImage())) {
-							requester.cancelDownload(context, feed.getImage());
-						}
-					}
-					// delete stored media files and mark them as read
-					List<FeedItem> queue = DBReader.getQueue(context);
-					boolean queueWasModified = false;
-					if (feed.getItems() == null) {
-						DBReader.getFeedItemList(context, feed);
-					}
-
-					for (FeedItem item : feed.getItems()) {
-						queueWasModified |= queue.remove(item);
-						if (item.getMedia() != null
-								&& item.getMedia().isDownloaded()) {
-							File mediaFile = new File(item.getMedia()
-									.getFile_url());
-							mediaFile.delete();
-						} else if (item.getMedia() != null
-								&& requester.isDownloadingFile(item.getMedia())) {
-							requester.cancelDownload(context, item.getMedia());
-						}
-					}
-					if (queueWasModified) {
-						adapter.setQueue(queue);
-					}
-					adapter.removeFeed(feed);
-					adapter.close();
-					EventDistributor.getInstance().sendFeedUpdateBroadcast();
-				}
-			}
-		});
-	}
-
-	public static void clearPlaybackHistory(final Context context) {
-		dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				adapter.clearPlaybackHistory();
-				adapter.close();
-				EventDistributor.getInstance()
-						.sendPlaybackHistoryUpdateBroadcast();
-			}
-		});
-	}
-
-	public static void addItemToPlaybackHistory(final Context context,
-			final FeedItem item) {
-		if (item.hasMedia()
-				&& item.getMedia().getPlaybackCompletionDate() != null) {
-			if (AppConfig.DEBUG)
-				Log.d(TAG, "Adding new item to playback history");
-			EventDistributor.getInstance().sendPlaybackHistoryUpdateBroadcast();
-		}
-
-	}
-
-	private static void cleanupDownloadLog(final PodDBAdapter adapter) {
-		final int DOWNLOAD_LOG_SIZE = 50;
-		final long logSize = adapter.getDownloadLogSize();
-		if (logSize > DOWNLOAD_LOG_SIZE) {
-			if (AppConfig.DEBUG)
-				Log.d(TAG, "Cleaning up download log");
-			adapter.removeDownloadLogItems(logSize - DOWNLOAD_LOG_SIZE);
-		}
-	}
-
-	public static void addDownloadStatus(final Context context,
-			final DownloadStatus status) {
-		dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-
-				PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-
-				adapter.setDownloadStatus(status);
-				cleanupDownloadLog(adapter);
-				adapter.close();
-				EventDistributor.getInstance().sendDownloadLogUpdateBroadcast();
-			}
-		});
-
-	}
-
-	public static void addQueueItemAt(final Context context, final long itemId,
-			final int index, final boolean performAutoDownload) {
-		dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				final PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				final List<FeedItem> queue = DBReader
-						.getQueue(context, adapter);
-				FeedItem item = null;
-
-				if (queue != null) {
-					boolean queueModified = false;
-					boolean unreadItemsModfied = false;
-
-					if (!itemListContains(queue, itemId)) {
-						item = DBReader.getFeedItem(context, itemId);
-						if (item != null) {
-							queue.add(index, item);
-							queueModified = true;
-							if (!item.isRead()) {
-								item.setRead(true);
-								unreadItemsModfied = true;
-							}
-						}
-					}
-					if (queueModified) {
-						adapter.setQueue(queue);
-						EventDistributor.getInstance()
-								.sendQueueUpdateBroadcast();
-					}
-					if (unreadItemsModfied && item != null) {
-						adapter.setSingleFeedItem(item);
-						EventDistributor.getInstance()
-								.sendUnreadItemsUpdateBroadcast();
-					}
-				}
-				adapter.close();
-				if (performAutoDownload) {
-
-					new Thread() {
-						@Override
-						public void run() {
-							DBTasks.autodownloadUndownloadedItems(context);
-
-						}
-					}.start();
-				}
-
-			}
-		});
-
-	}
-
-	public static void addQueueItem(final Context context,
-			final long... itemIds) {
-		if (itemIds.length > 0) {
-			dbExec.submit(new Runnable() {
-
-				@Override
-				public void run() {
-					final PodDBAdapter adapter = new PodDBAdapter(context);
-					adapter.open();
-					final List<FeedItem> queue = DBReader.getQueue(context,
-							adapter);
-
-					if (queue != null) {
-						boolean queueModified = false;
-						boolean unreadItemsModfied = false;
-						List<FeedItem> itemsToSave = new LinkedList<FeedItem>();
-						for (int i = 0; i < itemIds.length; i++) {
-							if (!itemListContains(queue, itemIds[i])) {
-								final FeedItem item = DBReader.getFeedItem(
-										context, itemIds[i]);
-
-								if (item != null) {
-									queue.add(item);
-									queueModified = true;
-									if (!item.isRead()) {
-										item.setRead(true);
-										itemsToSave.add(item);
-										unreadItemsModfied = true;
-									}
-								}
-							}
-						}
-						if (queueModified) {
-							adapter.setQueue(queue);
-							EventDistributor.getInstance()
-									.sendQueueUpdateBroadcast();
-						}
-						if (unreadItemsModfied) {
-							adapter.setFeedItemlist(itemsToSave);
-							EventDistributor.getInstance()
-									.sendUnreadItemsUpdateBroadcast();
-						}
-					}
-					adapter.close();
-					new Thread() {
-						@Override
-						public void run() {
-							DBTasks.autodownloadUndownloadedItems(context);
-
-						}
-					}.start();
-				}
-			});
-		}
-	}
-
-	public static void clearQueue(final Context context) {
-		dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				adapter.clearQueue();
-				adapter.close();
-
-				EventDistributor.getInstance().sendQueueUpdateBroadcast();
-			}
-		});
-	}
-
-	public static void removeQueueItem(final Context context,
-			final long itemId, final boolean performAutoDownload) {
-		dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				final PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				final List<FeedItem> queue = DBReader
-						.getQueue(context, adapter);
-				FeedItem item = null;
-
-				if (queue != null) {
-					boolean queueModified = false;
+    private static final String TAG = "DBWriter";
+
+    private static final ExecutorService dbExec;
+
+    static {
+        dbExec = Executors.newSingleThreadExecutor(new ThreadFactory() {
+
+            @Override
+            public Thread newThread(Runnable r) {
+                Thread t = new Thread(r);
+                t.setPriority(Thread.MIN_PRIORITY);
+                return t;
+            }
+        });
+    }
+
+    private DBWriter() {
+    }
+
+    /**
+     * Deletes a downloaded FeedMedia file from the storage device.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param mediaId ID of the FeedMedia object whose downloaded file should be deleted.
+     */
+    public static Future<?> deleteFeedMediaOfItem(final Context context,
+                                                  final long mediaId) {
+        return dbExec.submit(new Runnable() {
+            @Override
+            public void run() {
+
+                final FeedMedia media = DBReader.getFeedMedia(context, mediaId);
+                if (media != null) {
+                    boolean result = false;
+                    if (media.isDownloaded()) {
+                        // delete downloaded media file
+                        File mediaFile = new File(media.getFile_url());
+                        if (mediaFile.exists()) {
+                            result = mediaFile.delete();
+                        }
+                        media.setDownloaded(false);
+                        media.setFile_url(null);
+                        setFeedMedia(context, media);
+
+                        // If media is currently being played, change playback
+                        // type to 'stream' and shutdown playback service
+                        SharedPreferences prefs = PreferenceManager
+                                .getDefaultSharedPreferences(context);
+                        if (PlaybackPreferences.getCurrentlyPlayingMedia() == FeedMedia.PLAYABLE_TYPE_FEEDMEDIA) {
+                            if (media.getId() == PlaybackPreferences
+                                    .getCurrentlyPlayingFeedMediaId()) {
+                                SharedPreferences.Editor editor = prefs.edit();
+                                editor.putBoolean(
+                                        PlaybackPreferences.PREF_CURRENT_EPISODE_IS_STREAM,
+                                        true);
+                                editor.commit();
+                            }
+                            if (PlaybackPreferences
+                                    .getCurrentlyPlayingFeedMediaId() == media
+                                    .getId()) {
+                                context.sendBroadcast(new Intent(
+                                        PlaybackService.ACTION_SHUTDOWN_PLAYBACK_SERVICE));
+                            }
+                        }
+                    }
+                    if (AppConfig.DEBUG)
+                        Log.d(TAG, "Deleting File. Result: " + result);
+                }
+            }
+        });
+    }
+
+    /**
+     * Deletes a Feed and all downloaded files of its components like images and downloaded episodes.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param feedId  ID of the Feed that should be deleted.
+     */
+    public static Future<?> deleteFeed(final Context context, final long feedId) {
+        return dbExec.submit(new Runnable() {
+            @Override
+            public void run() {
+                DownloadRequester requester = DownloadRequester.getInstance();
+                SharedPreferences prefs = PreferenceManager
+                        .getDefaultSharedPreferences(context
+                                .getApplicationContext());
+                final Feed feed = DBReader.getFeed(context, feedId);
+                if (feed != null) {
+                    if (PlaybackPreferences.getCurrentlyPlayingMedia() == FeedMedia.PLAYABLE_TYPE_FEEDMEDIA
+                            && PlaybackPreferences.getLastPlayedFeedId() == feed
+                            .getId()) {
+                        context.sendBroadcast(new Intent(
+                                PlaybackService.ACTION_SHUTDOWN_PLAYBACK_SERVICE));
+                        SharedPreferences.Editor editor = prefs.edit();
+                        editor.putLong(
+                                PlaybackPreferences.PREF_CURRENTLY_PLAYING_FEED_ID,
+                                -1);
+                        editor.commit();
+                    }
+
+                    PodDBAdapter adapter = new PodDBAdapter(context);
+                    adapter.open();
+                    // delete image file
+                    if (feed.getImage() != null) {
+                        if (feed.getImage().isDownloaded()
+                                && feed.getImage().getFile_url() != null) {
+                            File imageFile = new File(feed.getImage()
+                                    .getFile_url());
+                            imageFile.delete();
+                        } else if (requester.isDownloadingFile(feed.getImage())) {
+                            requester.cancelDownload(context, feed.getImage());
+                        }
+                    }
+                    // delete stored media files and mark them as read
+                    List<FeedItem> queue = DBReader.getQueue(context);
+                    boolean queueWasModified = false;
+                    if (feed.getItems() == null) {
+                        DBReader.getFeedItemList(context, feed);
+                    }
+
+                    for (FeedItem item : feed.getItems()) {
+                        queueWasModified |= queue.remove(item);
+                        if (item.getMedia() != null
+                                && item.getMedia().isDownloaded()) {
+                            File mediaFile = new File(item.getMedia()
+                                    .getFile_url());
+                            mediaFile.delete();
+                        } else if (item.getMedia() != null
+                                && requester.isDownloadingFile(item.getMedia())) {
+                            requester.cancelDownload(context, item.getMedia());
+                        }
+                    }
+                    if (queueWasModified) {
+                        adapter.setQueue(queue);
+                    }
+                    adapter.removeFeed(feed);
+                    adapter.close();
+                    EventDistributor.getInstance().sendFeedUpdateBroadcast();
+                }
+            }
+        });
+    }
+
+    /**
+     * Deletes the entire playback history.
+     *
+     * @param context A context that is used for opening a database connection.
+     */
+    public static Future<?> clearPlaybackHistory(final Context context) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                adapter.clearPlaybackHistory();
+                adapter.close();
+                EventDistributor.getInstance()
+                        .sendPlaybackHistoryUpdateBroadcast();
+            }
+        });
+    }
+
+    /**
+     * Adds a FeedMedia object to the playback history. A FeedMedia object is in the playback history if
+     * its playback completion date is set to a non-null value. This method will set the playback completion date to the
+     * current date regardless of the current value.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param media   FeedMedia that should be added to the playback history.
+     */
+    public static Future<?> addItemToPlaybackHistory(final Context context,
+                                                     final FeedMedia media) {
+        return dbExec.submit(new Runnable() {
+            @Override
+            public void run() {
+                if (AppConfig.DEBUG)
+                    Log.d(TAG, "Adding new item to playback history");
+                media.setPlaybackCompletionDate(new Date());
+                PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                adapter.setMedia(media);
+                adapter.close();
+                EventDistributor.getInstance().sendPlaybackHistoryUpdateBroadcast();
+
+            }
+        });
+    }
+
+    private static void cleanupDownloadLog(final PodDBAdapter adapter) {
+        final long logSize = adapter.getDownloadLogSize();
+        if (logSize > DBReader.DOWNLOAD_LOG_SIZE) {
+            if (AppConfig.DEBUG)
+                Log.d(TAG, "Cleaning up download log");
+            adapter.removeDownloadLogItems(logSize - DBReader.DOWNLOAD_LOG_SIZE);
+        }
+    }
+
+    /**
+     * Adds a Download status object to the download log.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param status  The DownloadStatus object.
+     */
+    public static Future<?> addDownloadStatus(final Context context,
+                                              final DownloadStatus status) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+
+                PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+
+                adapter.setDownloadStatus(status);
+                cleanupDownloadLog(adapter);
+                adapter.close();
+                EventDistributor.getInstance().sendDownloadLogUpdateBroadcast();
+            }
+        });
+
+    }
+
+    /**
+     * Inserts a FeedItem in the queue at the specified index. The 'read'-attribute of the FeedItem will be set to
+     * true. If the FeedItem is already in the queue, the queue will not be modified.
+     *
+     * @param context             A context that is used for opening a database connection.
+     * @param itemId              ID of the FeedItem that should be added to the queue.
+     * @param index               Destination index. Must be in range 0..queue.size()
+     * @param performAutoDownload True if an auto-download process should be started after the operation
+     * @throws IndexOutOfBoundsException if index < 0 || index >= queue.size()
+     */
+    public static Future<?> addQueueItemAt(final Context context, final long itemId,
+                                           final int index, final boolean performAutoDownload) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                final PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                final List<FeedItem> queue = DBReader
+                        .getQueue(context, adapter);
+                FeedItem item = null;
+
+                if (queue != null) {
+                    boolean queueModified = false;
+                    boolean unreadItemsModified = false;
+
+                    if (!itemListContains(queue, itemId)) {
+                        item = DBReader.getFeedItem(context, itemId);
+                        if (item != null) {
+                            queue.add(index, item);
+                            queueModified = true;
+                            if (!item.isRead()) {
+                                item.setRead(true);
+                                unreadItemsModified = true;
+                            }
+                        }
+                    }
+                    if (queueModified) {
+                        adapter.setQueue(queue);
+                        EventDistributor.getInstance()
+                                .sendQueueUpdateBroadcast();
+                    }
+                    if (unreadItemsModified && item != null) {
+                        adapter.setSingleFeedItem(item);
+                        EventDistributor.getInstance()
+                                .sendUnreadItemsUpdateBroadcast();
+                    }
+                }
+                adapter.close();
+                if (performAutoDownload) {
+
+                    new Thread() {
+                        @Override
+                        public void run() {
+                            DBTasks.autodownloadUndownloadedItems(context);
+
+                        }
+                    }.start();
+                }
+
+            }
+        });
+
+    }
+
+    /**
+     * Appends FeedItem objects to the end of the queue. The 'read'-attribute of all items will be set to true.
+     * If a FeedItem is already in the queue, the FeedItem will not change its position in the queue.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param itemIds IDs of the FeedItem objects that should be added to the queue.
+     */
+    public static Future<?> addQueueItem(final Context context,
+                                         final long... itemIds) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                if (itemIds.length > 0) {
+                    final PodDBAdapter adapter = new PodDBAdapter(context);
+                    adapter.open();
+                    final List<FeedItem> queue = DBReader.getQueue(context,
+                            adapter);
+
+                    if (queue != null) {
+                        boolean queueModified = false;
+                        boolean unreadItemsModified = false;
+                        List<FeedItem> itemsToSave = new LinkedList<FeedItem>();
+                        for (int i = 0; i < itemIds.length; i++) {
+                            if (!itemListContains(queue, itemIds[i])) {
+                                final FeedItem item = DBReader.getFeedItem(
+                                        context, itemIds[i]);
+
+                                if (item != null) {
+                                    queue.add(item);
+                                    queueModified = true;
+                                    if (!item.isRead()) {
+                                        item.setRead(true);
+                                        itemsToSave.add(item);
+                                        unreadItemsModified = true;
+                                    }
+                                }
+                            }
+                        }
+                        if (queueModified) {
+                            adapter.setQueue(queue);
+                            EventDistributor.getInstance()
+                                    .sendQueueUpdateBroadcast();
+                        }
+                        if (unreadItemsModified) {
+                            adapter.setFeedItemlist(itemsToSave);
+                            EventDistributor.getInstance()
+                                    .sendUnreadItemsUpdateBroadcast();
+                        }
+                    }
+                    adapter.close();
+                    new Thread() {
+                        @Override
+                        public void run() {
+                            DBTasks.autodownloadUndownloadedItems(context);
+
+                        }
+                    }.start();
+                }
+            }
+        });
+
+    }
+
+    /**
+     * Removes all FeedItem objects from the queue.
+     *
+     * @param context A context that is used for opening a database connection.
+     */
+    public static Future<?> clearQueue(final Context context) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                adapter.clearQueue();
+                adapter.close();
+
+                EventDistributor.getInstance().sendQueueUpdateBroadcast();
+            }
+        });
+    }
+
+    /**
+     * Removes a FeedItem object from the queue.
+     *
+     * @param context             A context that is used for opening a database connection.
+     * @param itemId              ID of the FeedItem that should be removed.
+     * @param performAutoDownload true if an auto-download process should be started after the operation.
+     */
+    public static Future<?> removeQueueItem(final Context context,
+                                            final long itemId, final boolean performAutoDownload) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                final PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                final List<FeedItem> queue = DBReader
+                        .getQueue(context, adapter);
+                FeedItem item = null;
+
+                if (queue != null) {
+                    boolean queueModified = false;
                     QueueAccess queueAccess = QueueAccess.ItemListAccess(queue);
                     if (queueAccess.contains(itemId)) {
-						item = DBReader.getFeedItem(context, itemId);
-						if (item != null) {
-							queueModified = queueAccess.remove(itemId);
-						}
-					}
-					if (queueModified) {
-						adapter.setQueue(queue);
-						EventDistributor.getInstance()
-								.sendQueueUpdateBroadcast();
-					} else {
+                        item = DBReader.getFeedItem(context, itemId);
+                        if (item != null) {
+                            queueModified = queueAccess.remove(itemId);
+                        }
+                    }
+                    if (queueModified) {
+                        adapter.setQueue(queue);
+                        EventDistributor.getInstance()
+                                .sendQueueUpdateBroadcast();
+                    } else {
                         Log.w(TAG, "Queue was not modified by call to removeQueueItem");
                     }
-				} else {
+                } else {
                     Log.e(TAG, "removeQueueItem: Could not load queue");
                 }
-				adapter.close();
-				if (performAutoDownload) {
+                adapter.close();
+                if (performAutoDownload) {
 
-					new Thread() {
-						@Override
-						public void run() {
-							DBTasks.autodownloadUndownloadedItems(context);
+                    new Thread() {
+                        @Override
+                        public void run() {
+                            DBTasks.autodownloadUndownloadedItems(context);
 
-						}
-					}.start();
-				}
-			}
-		});
+                        }
+                    }.start();
+                }
+            }
+        });
 
-	}
+    }
 
-	public static void moveQueueItem(final Context context, final int from,
-			final int to, final boolean broadcastUpdate) {
-		dbExec.submit(new Runnable() {
+    /**
+     * Changes the position of a FeedItem in the queue.
+     *
+     * @param context         A context that is used for opening a database connection.
+     * @param from            Source index. Must be in range 0..queue.size()-1.
+     * @param to              Destination index. Must be in range 0..queue.size()-1.
+     * @param broadcastUpdate true if this operation should trigger a QueueUpdateBroadcast. This option should be set to
+     *                        false if the caller wants to avoid unexpected updates of the GUI.
+     * @throws IndexOutOfBoundsException if (to < 0 || to >= queue.size()) || (from < 0 || from >= queue.size())
+     */
+    public static Future<?> moveQueueItem(final Context context, final int from,
+                                          final int to, final boolean broadcastUpdate) {
+        return dbExec.submit(new Runnable() {
 
-			@Override
-			public void run() {
-				final PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				final List<FeedItem> queue = DBReader
-						.getQueue(context, adapter);
+            @Override
+            public void run() {
+                final PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                final List<FeedItem> queue = DBReader
+                        .getQueue(context, adapter);
 
-				if (queue != null) {
-					if (from >= 0 && from < queue.size() && to >= 0
-							&& to < queue.size()) {
+                if (queue != null) {
+                    if (from >= 0 && from < queue.size() && to >= 0
+                            && to < queue.size()) {
 
-						final FeedItem item = queue.remove(from);
-						queue.add(to, item);
+                        final FeedItem item = queue.remove(from);
+                        queue.add(to, item);
 
                         adapter.setQueue(queue);
-						if (broadcastUpdate) {
-							EventDistributor.getInstance()
-									.sendQueueUpdateBroadcast();
-						}
+                        if (broadcastUpdate) {
+                            EventDistributor.getInstance()
+                                    .sendQueueUpdateBroadcast();
+                        }
 
-					}
-				} else {
+                    }
+                } else {
                     Log.e(TAG, "moveQueueItem: Could not load queue");
                 }
-				adapter.close();
-			}
-		});
-	}
+                adapter.close();
+            }
+        });
+    }
 
-    public static void markItemRead(Context context, FeedItem item, boolean read, boolean resetMediaPosition) {
+    /**
+     * Sets the 'read'-attribute of a FeedItem to the specified value.
+     *
+     * @param context            A context that is used for opening a database connection.
+     * @param item               The FeedItem object
+     * @param read               New value of the 'read'-attribute
+     * @param resetMediaPosition true if this method should also reset the position of the FeedItem's FeedMedia object.
+     *                           If the FeedItem has no FeedMedia object, this parameter will be ignored.
+     */
+    public static Future<?> markItemRead(Context context, FeedItem item, boolean read, boolean resetMediaPosition) {
         long mediaId = (item.hasMedia()) ? item.getMedia().getId() : 0;
-        markItemRead(context, item.getId(), read, mediaId, resetMediaPosition);
+        return markItemRead(context, item.getId(), read, mediaId, resetMediaPosition);
+    }
+
+    /**
+     * Sets the 'read'-attribute of a FeedItem to the specified value.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param itemId  ID of the FeedItem
+     * @param read    New value of the 'read'-attribute
+     */
+    public static Future<?> markItemRead(final Context context, final long itemId,
+                                         final boolean read) {
+        return markItemRead(context, itemId, read, 0, false);
     }
 
-	public static void markItemRead(final Context context, final long itemId,
-			final boolean read) {
-		markItemRead(context, itemId, read, 0, false);
-	}
-
-	public static void markItemRead(final Context context, final long itemId,
-			final boolean read, final long mediaId,
-			final boolean resetMediaPosition) {
-		dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				final PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				adapter.setFeedItemRead(read, itemId, mediaId,
-						resetMediaPosition);
-				adapter.close();
-
-				EventDistributor.getInstance().sendUnreadItemsUpdateBroadcast();
-			}
-		});
-	}
-
-	public static void markFeedRead(final Context context, final long feedId) {
-		dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				final PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				Cursor itemCursor = adapter.getAllItemsOfFeedCursor(feedId);
-				long[] itemIds = new long[itemCursor.getCount()];
-				itemCursor.moveToFirst();
-				for (int i = 0; i < itemIds.length; i++) {
-					itemIds[i] = itemCursor.getLong(PodDBAdapter.KEY_ID_INDEX);
-				}
-				itemCursor.close();
-				adapter.setFeedItemRead(true, itemIds);
-				adapter.close();
-
-				EventDistributor.getInstance().sendUnreadItemsUpdateBroadcast();
-			}
-		});
-
-	}
-
-	public static void markAllItemsRead(final Context context) {
-		dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				final PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				Cursor itemCursor = adapter.getUnreadItemsCursor();
-				long[] itemIds = new long[itemCursor.getCount()];
-				itemCursor.moveToFirst();
-				for (int i = 0; i < itemIds.length; i++) {
-					itemIds[i] = itemCursor.getLong(PodDBAdapter.KEY_ID_INDEX);
-				}
-				itemCursor.close();
-				adapter.setFeedItemRead(true, itemIds);
-				adapter.close();
-
-				EventDistributor.getInstance().sendUnreadItemsUpdateBroadcast();
-			}
-		});
-
-	}
-
-	static Future<?> addNewFeed(final Context context, final Feed feed) {
-		return dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				final PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				adapter.setCompleteFeed(feed);
-				adapter.close();
-
-				EventDistributor.getInstance().sendFeedUpdateBroadcast();
-			}
-		});
-	}
-	
-	static Future<?> setCompleteFeed(final Context context, final Feed feed) {
-		return dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				adapter.setCompleteFeed(feed);
-				adapter.close();
-				
-				EventDistributor.getInstance().sendFeedUpdateBroadcast();
-			}});
-
-	}
-
-	public static Future<?> setFeedMedia(final Context context,
-			final FeedMedia media) {
-		return dbExec.submit(new Runnable() {
-
-			@Override
-			public void run() {
-				PodDBAdapter adapter = new PodDBAdapter(context);
-				adapter.open();
-				adapter.setMedia(media);
-				adapter.close();
-			}});
-	}
+    private static Future<?> markItemRead(final Context context, final long itemId,
+                                          final boolean read, final long mediaId,
+                                          final boolean resetMediaPosition) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                final PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                adapter.setFeedItemRead(read, itemId, mediaId,
+                        resetMediaPosition);
+                adapter.close();
+
+                EventDistributor.getInstance().sendUnreadItemsUpdateBroadcast();
+            }
+        });
+    }
 
+    /**
+     * Sets the 'read'-attribute of all FeedItems of a specific Feed to true.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param feedId  ID of the Feed.
+     */
+    public static Future<?> markFeedRead(final Context context, final long feedId) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                final PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                Cursor itemCursor = adapter.getAllItemsOfFeedCursor(feedId);
+                long[] itemIds = new long[itemCursor.getCount()];
+                itemCursor.moveToFirst();
+                for (int i = 0; i < itemIds.length; i++) {
+                    itemIds[i] = itemCursor.getLong(PodDBAdapter.KEY_ID_INDEX);
+                }
+                itemCursor.close();
+                adapter.setFeedItemRead(true, itemIds);
+                adapter.close();
+
+                EventDistributor.getInstance().sendUnreadItemsUpdateBroadcast();
+            }
+        });
+
+    }
+
+    /**
+     * Sets the 'read'-attribute of all FeedItems to true.
+     *
+     * @param context A context that is used for opening a database connection.
+     */
+    public static Future<?> markAllItemsRead(final Context context) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                final PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                Cursor itemCursor = adapter.getUnreadItemsCursor();
+                long[] itemIds = new long[itemCursor.getCount()];
+                itemCursor.moveToFirst();
+                for (int i = 0; i < itemIds.length; i++) {
+                    itemIds[i] = itemCursor.getLong(PodDBAdapter.KEY_ID_INDEX);
+                }
+                itemCursor.close();
+                adapter.setFeedItemRead(true, itemIds);
+                adapter.close();
+
+                EventDistributor.getInstance().sendUnreadItemsUpdateBroadcast();
+            }
+        });
+
+    }
+
+    static Future<?> addNewFeed(final Context context, final Feed feed) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                final PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                adapter.setCompleteFeed(feed);
+                adapter.close();
+
+                EventDistributor.getInstance().sendFeedUpdateBroadcast();
+            }
+        });
+    }
+
+    static Future<?> setCompleteFeed(final Context context, final Feed feed) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                adapter.setCompleteFeed(feed);
+                adapter.close();
+
+                EventDistributor.getInstance().sendFeedUpdateBroadcast();
+            }
+        });
+
+    }
+
+    /**
+     * Saves a FeedMedia object in the database. This method will save all attributes of the FeedMedia object. The
+     * contents of FeedComponent-attributes (e.g. the FeedMedia's 'item'-attribute) will not be saved.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param media   The FeedMedia object.
+     */
+    public static Future<?> setFeedMedia(final Context context,
+                                         final FeedMedia media) {
+        return dbExec.submit(new Runnable() {
+
+            @Override
+            public void run() {
+                PodDBAdapter adapter = new PodDBAdapter(context);
+                adapter.open();
+                adapter.setMedia(media);
+                adapter.close();
+            }
+        });
+    }
+
+    /**
+     * Saves only value of the 'position'-attribute of a FeedMedia object.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param media   The FeedMedia object.
+     */
     public static Future<?> setFeedMediaPosition(final Context context, final FeedMedia media) {
-        return dbExec.submit(new Runnable(){
+        return dbExec.submit(new Runnable() {
             @Override
             public void run() {
                 PodDBAdapter adapter = new PodDBAdapter(context);
@@ -543,8 +671,15 @@ public class DBWriter {
         });
     }
 
+    /**
+     * Saves a FeedItem object in the database. This method will save all attributes of the FeedItem object including
+     * the content of FeedComponent-attributes.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param item    The FeedItem object.
+     */
     public static Future<?> setFeedItem(final Context context,
-                                  final FeedItem item) {
+                                        final FeedItem item) {
         return dbExec.submit(new Runnable() {
 
             @Override
@@ -553,11 +688,19 @@ public class DBWriter {
                 adapter.open();
                 adapter.setSingleFeedItem(item);
                 adapter.close();
-            }});
+            }
+        });
     }
 
+    /**
+     * Saves a FeedImage object in the database. This method will save all attributes of the FeedImage object. The
+     * contents of FeedComponent-attributes (e.g. the FeedImages's 'feed'-attribute) will not be saved.
+     *
+     * @param context A context that is used for opening a database connection.
+     * @param image   The FeedImage object.
+     */
     public static Future<?> setFeedImage(final Context context,
-                                        final FeedImage image) {
+                                         final FeedImage image) {
         return dbExec.submit(new Runnable() {
 
             @Override
@@ -566,15 +709,16 @@ public class DBWriter {
                 adapter.open();
                 adapter.setImage(image);
                 adapter.close();
-            }});
+            }
+        });
     }
 
-	private static boolean itemListContains(List<FeedItem> items, long itemId) {
-		for (FeedItem item : items) {
-			if (item.getId() == itemId) {
-				return true;
-			}
-		}
-		return false;
-	}
+    private static boolean itemListContains(List<FeedItem> items, long itemId) {
+        for (FeedItem item : items) {
+            if (item.getId() == itemId) {
+                return true;
+            }
+        }
+        return false;
+    }
 }
diff --git a/src/de/danoeh/antennapod/storage/PodDBAdapter.java b/src/de/danoeh/antennapod/storage/PodDBAdapter.java
index a0c6cb11f..ac9309674 100644
--- a/src/de/danoeh/antennapod/storage/PodDBAdapter.java
+++ b/src/de/danoeh/antennapod/storage/PodDBAdapter.java
@@ -438,7 +438,7 @@ public class PodDBAdapter {
         }
         values.put(KEY_PUBDATE, item.getPubDate().getTime());
         values.put(KEY_PAYMENT_LINK, item.getPaymentLink());
-        if (item.getFeed().getId() == 0) {
+        if (item.getFeed() != null) {
             setFeed(item.getFeed());
         }
         values.put(KEY_FEED, item.getFeed().getId());
@@ -452,9 +452,7 @@ public class PodDBAdapter {
                     new String[]{String.valueOf(item.getId())});
         }
         if (item.getMedia() != null) {
-            if (item.getMedia().getId() == 0) {
                 setMedia(item.getMedia());
-            }
         }
         if (item.getChapters() != null) {
             setChapters(item);