NavigationController设置背景颜色白色 再加上

    if (@available(iOS 13.0, *)) {
        UINavigationBarAppearance *appearance = [[UINavigationBarAppearance alloc] init];
        [appearance configureWithOpaqueBackground];  // 确保背景不透明
        appearance.backgroundColor = [UIColor whiteColor];  // 设置背景为白色
        appearance.shadowImage = [[UIImage alloc] init];  // 移除底部横线
        appearance.shadowColor = nil;  // 移除底部阴影

        // 设置 standardAppearance
        nav.navigationBar.standardAppearance = appearance;

        // 设置 scrollEdgeAppearance 同样使用白色背景
        nav.navigationBar.scrollEdgeAppearance = nav.navigationBar.standardAppearance;
    } else {
        // 对于 iOS 13 以下版本，使用传统的设置方式
        [self.navigationController.navigationBar setBackgroundImage:[[UIImage alloc] init] forBarMetrics:UIBarMetricsDefault];
        self.navigationController.navigationBar.barTintColor = [UIColor whiteColor];
        self.navigationController.navigationBar.shadowImage = [[UIImage alloc] init];  // 移除底部横线
        self.navigationController.navigationBar.translucent = NO;
    }