在 iOS 6 中启用自动布局，同时保持向后兼容 iOS 5

问题描述

在利用 iOS 6 新的自动布局功能的同时，还能在早期版本的 iOS 上提供与旧设备的兼容性的最佳方式是什么?

可以在每个 .storyboard 或 .xib 文件上启用或禁用自动布局.只需选择特定文件并使用 Xcode 中的文件检查器修改使用自动布局"属性:

使用启用自动布局的接口文件并将部署目标设置为 6.0 之前的 iOS 版本会导致编译错误，例如:

MainStoryboard.storyboard:3 中的错误:iOS 6.0 之前版本的自动布局

在项目中使用自动布局并仍然保持与 iOS4-5 的兼容性的一种选择是创建两个 指出的那样，如果您从代码加载情节提要文件并且不使用主要Storyboard"设置在Xcode中设置初始storyboard，可以使用单个target.

对我来说，维护多个目标和接口文件所增加的复杂性成本似乎超过了使用自动布局的好处.除了少数特殊情况，如果需要 iOS4-5 兼容性，您可能最好使用普通的旧自动调整大小(或代码中的 layoutSubViews).

What is the best way to take advantage of the new auto layout features of iOS 6 while still providing compability with older devices on earlier versions of iOS?

Autolayout can be enabled or disabled on each .storyboard or .xib file. Just select the particular file and modify the "Use Autolayout" property using the File inspector in Xcode:

Using autolayout enabled interface files with the deployment target set to an iOS version prior to 6.0 results in compilation errors, e.g.:

Error in MainStoryboard.storyboard:3: Auto Layout on iOS Versions prior to 6.0

One of your options to use autolayout in a project and still preserve compatibility with iOS4-5 is to create two targets: one for deployment target iOS 6.0 and one for an earlier iOS version, e.g.:

You can create two versions for each of your storyboard and XIB files as well and use the autolayout enabled with the 6.0 target and the other with the legacy target, e.g.:

You then add MainStoryBoardAutoSize to the iOS6 target's Build phases and the other file to the iOS4 target. You can learn more about using multiple targets here.

EDIT: As marchinram's answer points out, if you load you storyboard files from code and do not use the "Main Storyboard" setting in Xcode to set the initial storyboard, you can use a single target.

For me, the cost of the added complexity of maintaining multiple targets and interface files seems to outweigh the benefits of using autolayout. Except for a few special cases, you are probably much better to use plain old auto sizing (or layoutSubViews from code) exclusively if iOS4-5 compatibility is required.

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