关于 presentViewController 时机

　　

　　类似微信、QQ这些应用如果用户没有登录，会弹出登录界面，如果 presentViewController 是写在  viewDidAppear 之前，会有警告

　　Presenting view controllers on detached view controllers is discouraged 

　　Unbalanced calls to begin/end appearance transitions for

 

     大致意思是Presenting控制器还没有完全出现就模态出一个视图，产生层级问题。

 

     将presentViewController写在视图已经出现就行 viewDidAppear 里

 

　　UIStoryboard 分类

• @implementation UIStoryboard (Extention)
  
  + (__kindofUIViewController *)wl_instantiateViewControllerWithStoryboardName:(NSString *)storyboardName
                                                                     identifier:(NSString *)identifier {
      NSAssert(storyboardName.length > 0, @"参数 storyboardName 为 nil 或空字符串.");
     
      UIStoryboard *storyboard = [selfstoryboardWithName:storyboardName bundle:nil];
     
      NSAssert(storyboard, @"文件不存在 => %@", [NSString stringWithFormat:@"%@.storyboard", storyboardName]);
     
      if (identifier) {
          return [storyboard instantiateViewControllerWithIdentifier:identifier];
      }
     
      UIViewController *initialVC = [storyboard instantiateInitialViewController];
     
      NSAssert(initialVC, @"%@ 未指定 initial 控制器.",
               [NSString stringWithFormat:@"%@.storyboard", storyboardName]);
     
      return initialVC;
  }
  
  @end
• 对于  (__kindofUIViewController *) 是返回值可以是 UIViewController 及其子类，毕竟有时候我们需要模态出来的视图需要包装NavigationController