UINavigationController

1、不自定义UINavigation更换背景色，可以直接设置naviagationBar的背景色，通过barTintColor 属性设置。

2、UINavigationController作为容器时，会导致子controller被遮挡，可以设置子Controller的 edgesForExtendedLayout 和 automaticallyAdjustScrollViewInsets(自视图是UIScrollView时)解决：

-(instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // 解决被UINavigationController遮挡
        if([[[UIDevice currentDevice]systemVersion]floatValue]>=7.0)
        {
            self.edgesForExtendedLayout = UIRectEdgeNone;
            self.automaticallyAdjustsScrollViewInsets = NO;
        }
    }
    return self;
}