去除导航底部线条

[self.navigationController.navigationBar.subviews
         enumerateObjectsUsingBlock:^(UIView
                                      *view, NSUInteger idx,
                                      BOOL *stop) {
             if ([[UIDevice currentDevice].systemVersion intValue]>=10){
                 //iOS10,改变了导航栏的私有接口为_UIBarBackground
                 if ([view
                      isKindOfClass:NSClassFromString(@"_UIBarBackground")])
                 {
                      [view.subviews
                                      lastObject].hidden = YES;
                     }
                 
             }else{
                     //iOS10之前使用的是_UINavigationBarBackground
                     if ([view
                          isKindOfClass:NSClassFromString(@"_UINavigationBarBackground")])
                     {
                         [view.subviews lastObject].hidden = YES;
                         }
                     }
             
         }];