I've developed an xposed module for whatsapp.
http://forum.xda-developers.com/xposed/modules/mod-whatsapp-extensions-add-extra-t3452784
I wanted to add feature to hide our own last seen still see others or report a fake last seen for eg: 1 Jan 1970.
I made following assumptions:
To do that first I hooked date and System.currentTimeInMillis methods to make whatsapp think its 1 Jan 1970. That worked but still last seen was shown perfectly.
Assumption: The last seen time value is directly taken from the server
Then I looked in the source to find where last_seen preference is referenced. Turns out it is only referenced in SettingsPrivacy activity's class.
Assumption: To hide our last seen and still see others we need to change last seen preference to 'visible to all' and turn that back to off once we get the last seen.
but the problem is it uses onPreferenceChangeListener. We cannot hook a method from the interface directly.
I cannot find the subclass which implements onPreferenceChangeListener as the classes shown in code are synthetic. Please if anyone can help me with this, it will be great. I need to find which is preferencechangelistener for that preference. Rest I will manage.
I found a way to do it and its working.
http://forum.xda-developers.com/xposed/modules/mod-whatsapp-extensions-add-extra-t3452784
The way to do it is by hooking a method which takes a preference as argument. We create a preference ( com.whatsapp.preference.WAprivacy preference to be precise ) and then pass this preference with last seen set to desired value to the method. And we are done. It is working so far.