ARC下 does not support automated __weak references错误

ARC下 does not support automated __weak references错误

此错误，通常是你的ARC下不支持weak 把你项目里面，weak的地方 改为 unsafe_unretained

参考：http://stackoverflow.com/questions/6893038/how-do-i-replace-weak-references-when-using-arc-and-targeting-ios-4-0