Do you know how to hide the 'back' button in a UINavigationController? Also, how to show it back, but I guess that's very similar to hiding it...
Just like the mail application does on the iPhone when you hit 'Edit' while viewing emails.
I just found out the answer, in a controller use this:
[self.navigationItem setHidesBackButton:YES animated:YES];
And to restore it:
[self.navigationItem setHidesBackButton:NO animated:YES];
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[UPDATE]
Swift 3.0:
self.navigationItem.setHidesBackButton(true, animated:true)