Hi,
1-first i want to thank Agustin Adami & Damian Cherubini for their advice and persistance about solving the problems i'm facing.
2-I modified the condition to "
subsysdetailsViewModel.Subsystem.SubsystemNo == Subsys.SubsystemNo"
where SubsystemNo is like id but duplication still exist.i think no problem with the condition with its previous state because
as i mentioned above it working in one case when i try to duplicate tabitem next to itself, duplication eleminated,
but if different tab in between duplication take place meaning that that condition compare the new tab under creation
with the previous one only not with all open tabs maybe there is a problem with looping through all open tabs.may be becuase
MEF create the objects where it should be created through view outside mef ...