uinavagation 透明代码

 NSShadow *shadow = [[NSShadow alloc] init];

    [shadow setShadowOffset:CGSizeMake(1, 1)];

    [shadow setShadowColor:[UIColor blackColor]];

    [shadow setShadowBlurRadius:1];

    self.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName: [UIColor blackColor], NSShadowAttributeName: shadow};

    [self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];

    self.navigationController.navigationBar.shadowImage = [UIImage new];