4.UINavigationBar的tintColor变了，backItem的颜色不变 的问题解决方案:

@interface UINavigationController (RefreshBackItem)
- (void)refreshBackItem;
@end

@implementation UINavigationController (RefreshBackItem)
- (void)refreshBackItem
{
    UINavigationBar *bar = self.navigationBar;
    UINavigationItem *backItem = bar.backItem;
    NSString *title = [backItem title];
    backItem.title = @"";
    backItem.title = title;
}
@end