如何在推送UINavigationController之后向UINavigationBar添加编辑按钮

I want to add the edit button of a table view to the navigation bar of a navigation controller after pushing this new table view on the navigation controller. When I do that, the edit button doesn't appear (I suspect the 'Back' button obscures it), and when I go back up the hierarchy, there it is, but now I have two of them (Edit Edit). My source code:I want to add the edit button of a table view t