WPF cancelling twoway binding

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WPF

Hello,

I have a ListBox with the name and address of my customers displayed in a data template. When I select an item it opens an edit form with other information. I am using two-way binding and have set the UpdateSourceTrigger=PropertyChanged.
I have a save and cancel button on the edit form. The save event persist the changes to the database.(linq to SQL)

How can I get the cancel event to undo the changes I have made in the edit form if I do not want to persist the changes? As it is now if I select cancel and display my listbox form. The changes are displayed.
My second dilemma is. I have validation on the edit form. However the changes still update the source even if it violates the validation rule. I tried setting the UpdateSourceTrigger=Explicit. When this was done. The errors on the UI were not working, E.g., I could clear the name field and no notification will show. This was not the case when I set UpdateSourceTrigger=PropertyChanged.
I welcome you help
Thanks