ios日期比较

 +(int)compareDate:(NSDate *)date1 date:(NSDate *)date2
 {
     NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
     [dateFormatter setDateFormat:@"yyyy-MM-dd"];
      //比较准确度为“日”，如果提高比较准确度，可以在此修改时间格式
     NSString *stringDate1 = [dateFormatter stringFromDate:date1];
     NSString *stringDate2 = [dateFormatter stringFromDate:date2];
     NSDate *dateA = [dateFormatter dateFromString:stringDate1];
     NSDate *dateB = [dateFormatter dateFromString:stringDate2];
     NSComparisonResult result = [dateA compare:dateB];
     if (result == NSOrderedDescending) {
         return ;  //date1 比 date2 晚
     } else if (result == NSOrderedAscending){
         return -; //date1 比 date2 早
     }
     return ; //在当前准确度下，两个时间一致
 }