@interface MDSpreadView : UIScrollView {
@private
id <MDSpreadViewDataSource> _dataSource;
}
@property (nonatomic, assign) IBOutlet id <MDSpreadViewDataSource> dataSource;
上面一段在编译时出现existing instance variable ‘_dataSource‘ for property ‘dataSource‘ with assign attribute must be __unsafe_unretained
将上一段改为
@interface MDSpreadView : UIScrollView {
@private
id <MDSpreadViewDataSource>__unsafe_unretained _dataSource;
}
@property (unsafe_unretained) IBOutlet id <MDSpreadViewDataSource> dataSource;
问题就可以解决在ARC工程引入非ARC时，出现__unsafe_unretained
原文：http://www.cnblogs.com/yintingting/p/4564766.html