工程启用ARC后,delegate不能设置成assign属性了,只能是unsafe_unretained么

//.h
id __unsafe_unretained _delegate;
@property(nonatomic,unsafe_unretained) id <EGORefreshTableHeaderDelegate> delegate;

//.m
@synthesize delegate=_delegate;

if (!_delegate) {
    return;
}

unsafe_unretained的指针应该如何避免对象指向丢失,一旦丢失,即使是上面的if判断调用都会crash,如何处理呢

求教!!!