系统版本从 10.9 更新到 10.10 后，cocoapods 安装就出问题了：
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require‘: cannot load such file -- xcodeproj/prebuilt/universal.x86_64-darwin14-2.0.0/xcodeproj_ext (LoadError)
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require‘ from /Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/lib/xcodeproj/ext.rb:6:in `rescue in <top (required)>‘ from /Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/lib/xcodeproj/ext.rb:3:in
`<top (required)>‘ from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require‘ from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in
`require‘ from /Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/lib/xcodeproj.rb:30:in `<top (required)>‘ from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require‘ from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in
`require‘ from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.33.1/lib/cocoapods.rb:2:in `<top (required)>‘ from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in `require‘ from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:55:in
`require‘ from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.33.1/bin/pod:32:in `<top (required)>‘ from /usr/bin/pod:23:in `load‘ from /usr/bin/pod:23:in `<main>‘
进行到这一步
$ pod install 就会报以上的错误发现只需要修改Podfile 文件platform :ios, ‘8.0‘ pod "AFNetworking", "~> 2.4"
将 pod "AFNetworking", "~> 2.0" 修改为 pod "AFNetworking", "~> 2"然后在终端输入 pod update 就可以正常导入AFNetworking 了。