UINavigationBar和UITabBar外观代理奇怪的结果

Question

当我使用单个代码中的以下代码时，UITabBar外观不能完全正常工作（根本不会改变），并且UINavigationBar外观正在任意改变，而不是根据切换情况。

#pragma mark - UITabBarController Delegate

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController
{
    NSLog(@"switch");
    switch ([tabBarController.viewControllers indexOfObject:viewController])
    {
        case 0:
            [[UINavigationBar appearance] setBackgroundImage:[UIColor imageWithColor:[AppConfiguration color3]] forBarMetrics:UIBarMetricsDefault];
            [[UITabBar appearance] setBarTintColor:[AppConfiguration color3]];
            break;
        case 1:
            [[UINavigationBar appearance] setBackgroundImage:[UIColor imageWithColor:[AppConfiguration color4]] forBarMetrics:UIBarMetricsDefault];
            [[UITabBar appearance] setBarTintColor:[AppConfiguration color4]];
            break;
        case 2:
            [[UINavigationBar appearance] setBackgroundImage:[UIColor imageWithColor:[AppConfiguration color5]] forBarMetrics:UIBarMetricsDefault];
            [[UITabBar appearance] setBarTintColor:[AppConfiguration color5]];
            break;

        default:
            NSLog(@"UITabBar index: %lu", (unsigned long)[tabBarController.viewControllers indexOfObject:viewController]);
            break;
    }
}