SNLoginViewController *loginVC = [[SNLoginViewController alloc] init];
SNLoginNavController *loginNavVC = [[SNLoginNavController alloc] initWithRootViewController:loginVC];
[self presentViewController:loginNavVC animated:YES completion:nil];

- (instancetype)initWithRootViewController:(UIViewController *)rootViewController {
    self = [super initWithRootViewController:rootViewController];
    if (self) {

        UIImage *bgImage = [UIImage imageNamed:@"bg"];
        UIImageView *bgImageView = [[UIImageView alloc] initWithImage:bgImage];
        bgImageView.frame = [UIScreen mainScreen].bounds;
        [self.view insertSubview:bgImageView atIndex:0];

        [self.navigationBar setBackgroundImage:[UIImage imageNamed:@"transparent"]//transparent is a transparent png
                             forBarMetrics:UIBarMetricsCompact];
        self.navigationBar.shadowImage = [UIImage imageNamed:@"transparent"];
        self.navigationBar.barStyle = UIBarStyleBlackTranslucent;

        [self.navigationBar setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor whiteColor], NSFontAttributeName: [UIFont systemFontOfSize:18]}];
        self.navigationBar.clipsToBounds = YES;
    }
    return self;
}