iOS SDK Release Notes for iOS 8.3 Beta 4 节选（UIKit）

（没有逐字逐词翻译，希望能够理解，如果有不对的，恳请指正）

UIKit

Note

注意

When linking against iOS 8.3, any code that relies on layout information (such as the frame) of a UIButton subview
when the button is not in the window hierarchy will need to send layoutIfNeeded to
the button before retrieving layout information (such as button.titleLabel.frame) to ensure that the
layout values are up to date.

在iOS8.3下编译链接的时候，如果UIButton(包括子类)不是窗口级别的控件，任何涉及获取和操作UIButton（包括子类）布局信息的代码，都应该先发送一个layoutIfNeeded事件（其实就是执行UIButton的layoutIfNeed方法）,以确保获取到的UIButton的布局信息是最新的。

For example, if you had something like this:

举例如下，如果iOS8.3以前，你这样写代码：

UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];

// code that sets up the button, but doesn’t yet add it to a window

CGRect titleFrame = button.titleLabel.frame;

// code that relies on the correct value for titleFrame

You now need:

那么，现在你需要这样写代码：

UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];

// code that sets up the button, but doesn’t yet add it to a window

[button layoutIfNeeded]; // This is also safe pre-iOS 8.3

CGRect titleFrame = button.titleLabel.frame;

// code that relies on the correct value for titleFrame