How to override self.navigationItem.backBarButtonItem Action?

STILL, No direct access for changing target and action on self.navigationItem.backBarButtonItem.

I ended up using the first one i tried... and get my (custom) image..

UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"myImage.png"]
                                                               style:UIBarButtonItemStyleBordered
                                                              target:self
                                                              action:@selector(backButtonOverrideAction:)];
[self.navigationItem setLeftBarButtonItem:backButton];

while...

//this two lines of code are still useless, i just feel sorry for them.. 
[self.navigationItem.backBarButtonItem setTarget:<#(id)#>];
[self.navigationItem.backBarButtonItem setAction:<#(SEL)#>];

You cannot assign action to back BarButton. The solution for that is to create the custom back button.

In swift 3.1

override func viewDidLoad() {    
// set navigationItem.leftBarButtonItem return to Root
let backToRootVCButton = UIBarButtonItem.init(title: "Back", style: UIBarButtonItemStyle.plain, target: self, action: #selector(backToRootVCAction))
self.navigationItem.setLeftBarButton(backToRootVCButton, animated: true)

}

func backToRootVCAction() {
    _ = self.navigationController?.popToRootViewController(animated: true)
}