我想找出核心数据中的对象,我的代码:
类型:
signedDate
(日期)
alarmDate
(日期)
starTime
(NS日期)
endTime
(NS日期)
NSString *str = @"(signedDate >= %@) AND (signedDate < %@) AND (alarmDate == nil)";
NSPredicate *predicate = [NSPredicate predicateWithFormat:str, starTime, endTime];
[request setPredicate:predicate];
NSArray *results=[context executeFetchRequest:request error:nil];
谓词错了?如何判断一个coredata对象是nil?谓词应该是什么?