一开始选了ARC，没关系"Build Settings" and turn off the option "Objective-C Automatic Reference Counting" NO
'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).