编译出现错误：
'release' is unavailable: not available in automatic reference counting mode..
解决办法：
You need to turn off Automatic
Reference Counting. You do this by clicking on your project in the
navigator (the top item in the finder-like thing on the left), then
click on your target, select "Build Settings" and turn off the option "Objective-C Automatic Reference Counting" (you
can use the search field on the upper right to search it).
单击工程名称，选择Build Settings下的Objective-c Automatic Reference Counting，将其调为No。如下图：
