UINavgationController 的backBarBu

    self.navigationController.navigationBar.tintColor = [UIColor whiteColor];

//    self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"" style:uibar target:self action:@""];

    self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStyleDone target:self action:nil];