I just saw in the Facebook SDK for iOS that they call [super layoutSubviews]; at the end and not at the beginning of the layoutSubviews method.

我刚刚在iOS版的Facebook SDK中看到，他们在layoutSubviews方法的结尾而不是开头调用[Super layoutSubviews]；。

As far as I know, we should always do it as the first line.
Can implementing it a different way cause any unexpected UI behavior?

据我所知，我们应该始终把它作为第一条线来做。以不同的方式实现它会导致任何意想不到的UI行为吗？

- (void)layoutSubviews
{
  CGSize size = self.bounds.size;
  CGSize longTitleSize = [self sizeThatFits:size title:[self _longLogInTitle]];
  NSString *title = (longTitleSize.width <= size.width ?
                     [self _longLogInTitle] :
                     [self _shortLogInTitle]);
  if (![title isEqualToString:[self titleForState:UIControlStateNormal]]) {
    [self setTitle:title forState:UIControlStateNormal];
  }

  [super layoutSubviews];
}

According to the UIView Class Reference,

根据UIView类引用，

The default implementation of this method does nothing on iOS 5.1 and earlier. Otherwise, the default implementation uses any constraints you have set to determine the size and position of any subviews.

Thus, that the Facebook SDK example app calls [super layoutSubviews] at the end of their implementation could be an artifact of the app being initially built for an iOS version prior to iOS 5.1.

因此，Facebook SDK示例应用程序在其实现结束时调用[Super layoutSubview]可能是该应用程序最初为iOS 5.1之前的iOS版本构建的产物。

For more recent versions of iOS, you should call [super layoutSubviews] at the beginning of your implementation. Otherwise, the superclass will rearrange your subviews after you do the custom layout, effectively ignoring your implementation of layoutSubviews().

对于较新版本的iOS，您应该在开始实施时调用[Super layoutSubview]。否则，超类将在您完成定制布局后重新排列您的子视图，从而有效地忽略您的layoutSubviews()的实现。

look into the code, before [super layoutSubviews], it is not about the frame. so put it at the end may work well too.
I guess the coder must want to check the title and modify the title based on some rules, he thinks everytime the layoutSubviews being called is a right opportunity to do that, so he put the code here.

仔细看看代码，在[Super layoutSubview]之前，它不是关于框架的。因此，把它放在最后可能也会起到很好的作用。我猜程序员一定想要检查标题并根据一些规则修改标题，他认为每次调用layoutSubview都是这样做的正确机会，所以他将代码放在这里。

You always have to call [super layoutSubviews] last, if the intrinsic content size of a view will be changed. If you change the title of the button, the intrinsic content size of the UIButton will be changed, therefore the last call.

如果要更改视图的固有内容大小，则始终必须最后调用[Super layoutSubviews]。如果您更改按钮的标题，UIButton的固有内容大小也会更改，因此是最后一次调用。

The first call to [super layoutSubviews] is always required because iOS updates the layout based on the constraints.
However, the technical most correct way of implementing your sample should be:

第一次调用[super layoutSubviews]总是必需的，因为iOS会根据约束更新布局。但是，实现示例的最正确的技术方法应该是：

- (void)layoutSubviews
{
 [super layoutSubviews];
  CGSize size = self.bounds.size;
  CGSize longTitleSize = [self sizeThatFits:size title:[self _longLogInTitle]];
  NSString *title = (longTitleSize.width <= size.width ?
                     [self _longLogInTitle] :
                     [self _shortLogInTitle]);
  if (![title isEqualToString:[self titleForState:UIControlStateNormal]]) {
    [self setTitle:title forState:UIControlStateNormal];
  }

  [super layoutSubviews];
}

I recommend "Programming iOS" Matt Neuberg. It's my source of truth when I have problems like this described here.

我推荐《编程iOS》的马特·纽伯格。当我遇到这里描述的这样的问题时，这是我的真理之源。

Here is the quote that describes the rule:

以下是描述该规则的引语：

(...) you might override layoutSubviews when you’re using autolayout, in order to tweak the outcome. A typical structure is: first you call super, causing all the subviews to adopt their new frames; then you examine those frames; if you don’t like the outcome, you can change things; and finally you call super again, to get a new layout outcome.

(page 80)

(page（第80条）