iOS15 如果配置了全局的导航器背景，后面针对某一个导航器修改背景没有效果

[empty]

假如全局设置的背景为红色

if (@available(iOS 15.0, *)) {
        UINavigationBarAppearance *app = [UINavigationBarAppearance new];
         [app configureWithDefaultBackground];
         app.backgroundColor = UIColor.redColor;
        [UINavigationBar appearance].scrollEdgeAppearance = app;
        [UINavigationBar appearance].standardAppearance = app;
    }

某一个vc的viewDidLoad方法中，需要修改成白色，没有效果。

    self.navigationController.navigationBar.translucent = NO;
    [self.navigationController.navigationBar setBackgroundImage:bgImg forBarMetrics:UIBarMetricsDefault];
    [self.navigationController.navigationBar setShadowImage:[UIImage new]];
    [self.navigationController.navigationBar setClipsToBounds:NO];

后来我找到导航器中的背景图片对象，设置bgImgView.image的值，在viewDidAppear中执行可以修改，但滑动返回的时候又被系统重置了，感觉系统在出现和消失的时候都会重置导航器的全局默认属性值。

     for (UIView * view in self.navigationController.navigationBar.subviews) {
            for (UIView * resultView in view.subviews) {
                if ([resultView isKindOfClass:[UIImageView class]]) {
                    UIImageView * bgImgView = (UIImageView*)resultView;
                    bgImgView.image = bgImg;
                    return;
                }
            }
        }

-----------------原来每一个vc也有对应的Appearance,这样设置就行了

if (@available(iOS 15.0, *)) {
        UINavigationBarAppearance *app = [UINavigationBarAppearance new];
            [app configureWithDefaultBackground];
        app.backgroundImage = bgImg;
        self.navigationItem.scrollEdgeAppearance = app;
        self.navigationItem.standardAppearance = app;
        return;
    }

[MyiOS]

这样有点麻烦啊