- (void)viewDidLoad {

    [super viewDidLoad];

    // Do any additional setup after loading the view, typically from a nib.

    //Add button to NavigationController

    UIBarButtonItem *backButton =

    [[UIBarButtonItem alloc] initWithTitle:NSLocalizedString(@"back", @"")

                                     style:UIBarButtonItemStylePlain

                                    target:self

                                    action:@selector(goBack)];

    self.navigationItem.leftBarButtonItem = backButton;

}

//Perform action on back Button

- (void) goBack {    // Go back task over-here

}

设置action？