diff -r 000000000000 -r fb9019fb1bf7 src/org/gege/caldavsyncadapter/Event.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/gege/caldavsyncadapter/Event.java	Tue Feb 10 18:12:00 2015 +0100
@@ -0,0 +1,184 @@
+/**
+ * Copyright (c) 2012-2013, Gerald Garcia, Timo Berger
+ * 
+ * This file is part of Andoid Caldav Sync Adapter Free.
+ *
+ * Andoid Caldav Sync Adapter Free is free software: you can redistribute 
+ * it and/or modify it under the terms of the GNU General Public License 
+ * as published by the Free Software Foundation, either version 3 of the 
+ * License, or at your option any later version.
+ *
+ * Andoid Caldav Sync Adapter Free is distributed in the hope that 
+ * it will be useful, but WITHOUT ANY WARRANTY; without even the implied 
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Andoid Caldav Sync Adapter Free.  
+ * If not, see <http://www.gnu.org/licenses/>.
+ * 
+ */
+package org.gege.caldavsyncadapter;
+
+import android.content.ContentValues;
+import android.provider.CalendarContract.Events;
+import android.util.Log;
+
+/**
+ * abstract class for Calendar and Android events 
+ */
+abstract public class Event {
+	private static final String TAG = "Event";
+	
+	/**
+	 * stores the ETAG of an event
+	 */
+	public static String ETAG = Events.SYNC_DATA1;
+
+	/**
+	 * internal Tag used to identify deleted events 
+	 */
+	public static String INTERNALTAG = Events.SYNC_DATA2;
+
+	/**
+	 * store the whole VEVENT in here
+	 * missing TAGs they might be missing for google update
+	 * 
+	 * CREATED:20130906T102857Z
+	 * DTSTAMP:20130906T102857Z
+	 * LAST-MODIFIED:20130906T102857Z
+	 * SEQUENCE:0
+	 */
+	public static String RAWDATA = Events.SYNC_DATA3;
+
+	/**
+	 * stores the UID of an Event
+	 * example: UID:e6be67c6-eff0-44f8-a1a0-6c2cb1029944-caldavsyncadapter
+	 */
+	public static String UID = Events.SYNC_DATA4;
+	
+	/**
+	 * the event transformed into ContentValues
+	 */
+	public ContentValues ContentValues = new ContentValues();
+	
+	abstract public String getETag();
+	abstract public void setETag(String ETag);
+
+	/**
+	 * returns a list of all items that are comparable with this sync adapter
+	 * @return a list of all items that are comparable with this sync adapter
+	 */
+	public static java.util.ArrayList<String> getComparableItems() {
+		java.util.ArrayList<String> Result = new java.util.ArrayList<String>();
+		Result.add(Events.DTSTART);
+		Result.add(Events.DTEND);
+		Result.add(Events.EVENT_TIMEZONE);
+		Result.add(Events.EVENT_END_TIMEZONE);
+		Result.add(Events.ALL_DAY);
+		Result.add(Events.DURATION);
+		Result.add(Events.TITLE);
+		Result.add(Events.CALENDAR_ID);
+		Result.add(Events._SYNC_ID);
+		//Result.add(Events.SYNC_DATA1);
+		Result.add(ETAG);
+		Result.add(Events.DESCRIPTION);
+		Result.add(Events.EVENT_LOCATION);
+		Result.add(Events.ACCESS_LEVEL);
+		Result.add(Events.STATUS);
+		Result.add(Events.RDATE);
+		Result.add(Events.RRULE);
+		Result.add(Events.EXRULE);
+		Result.add(Events.EXDATE);
+		Result.add(UID);
+		
+		return Result;
+	}
+	
+	/**
+	 * sets the AndroidCalendarId for this event
+	 * @param ID the AndroidCalendarId for this event
+	 */
+	public void setAndroidCalendarId(long ID) {
+		if (this.ContentValues.containsKey(Events.CALENDAR_ID))
+			this.ContentValues.remove(Events.CALENDAR_ID);
+		
+		this.ContentValues.put(Events.CALENDAR_ID, ID);
+	}
+
+	/**
+	 * returns the AndroidCalendarId for this event.
+	 * @return the AndroidCalendarId for this event
+	 */
+	public long getAndroidCalendarId() {
+		long Result = -1;
+		if (this.ContentValues.containsKey(Events.CALENDAR_ID))
+			Result = this.ContentValues.getAsLong(Events.CALENDAR_ID);
+		return Result;
+	}
+
+	/**
+	 * returns the UID for this event. you can also check, whether the UID was stored from server. the V1.7 release and before didn't save them.
+	 * example: UID:e6be67c6-eff0-44f8-a1a0-6c2cb1029944-caldavsyncadapter
+	 * @return the UID for this event
+	 */
+	public String getUID() {
+		String Result = "";
+		if (this.ContentValues.containsKey(UID))
+			Result = this.ContentValues.getAsString(UID);
+		
+		return Result;
+	}
+	
+	/**
+	 * compares the given ContentValues with the current ones for differences
+	 * @param calendarEventValues the contentValues of the calendar event
+	 * @return if the events are different
+	 */
+	public boolean checkEventValuesChanged(ContentValues calendarEventValues) {
+		boolean Result = false;
+		Object ValueAndroid = null;
+		Object ValueCalendar = null;
+		java.util.ArrayList<String> CompareItems = Event.getComparableItems();
+		
+		for (String Key: CompareItems) {
+
+			if (this.ContentValues.containsKey(Key)) 
+				ValueAndroid = this.ContentValues.get(Key);
+			else
+				ValueAndroid = null;
+
+			if (calendarEventValues.containsKey(Key))
+				ValueCalendar = calendarEventValues.get(Key);
+			else
+				ValueCalendar = null;
+
+			/*
+			 * TODO: Sync is designed to "Server always wins", should be a general option for this adapter
+			 */
+			if (ValueAndroid != null) {
+				if (ValueCalendar != null) {
+					if (!ValueAndroid.toString().equals(ValueCalendar.toString())) {
+						Log.d(TAG, "difference in " + Key.toString() + ":" + ValueAndroid.toString() + " <> " + ValueCalendar.toString());
+						this.ContentValues.put(Key,ValueCalendar.toString());
+						Result = true;
+					}
+				} else {
+					Log.d(TAG, "difference in " + Key.toString() + ":" + ValueAndroid.toString() + " <> null");
+					this.ContentValues.putNull(Key);
+					Result = true;
+				}
+			} else {
+				if (ValueCalendar != null) {
+					Log.d(TAG, "difference in " + Key.toString() + ":null <> " + ValueCalendar.toString());
+					this.ContentValues.put(Key, ValueCalendar.toString());
+					Result = true;
+				} else {
+					// both null -> this is ok
+				}
+			}
+		}
+		
+		return Result;
+	}
+}