iphone - 从指定日期起2天前发出NSNotification

我想在目标日期起2天前触发通知。目前，我正在使用以下代码来触发通知，但是有确切的方法在目标日期起2天前触发通知。

    NSString *frstdate = [[calenderarray objectAtIndex:k] objectForKey:@"date"];
    NSLog(@"frstdate..%@",frstdate);
    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"yyyy-MM-dd"];
    NSDate *date = [dateFormat dateFromString:frstdate];
    NSLog(@"date..%@",date);
    NSDate *dateToFire = [[[NSDate alloc] initWithTimeInterval:-24*60*60 sinceDate:date]autorelease];
     NSLog(@"dateToFire..%@",dateToFire);
    UILocalNotification *localNotif = [[UILocalNotification alloc] init];
    if (localNotif == nil)
         return;
    localNotif.fireDate = itemDate;
    localNotif.alertAction = @"View";
    localNotif.soundName = UILocalNotificationDefaultSoundName;
     localNotif.applicationIconBadgeNumber = 1;
     localNotif.userInfo = [NSDictionary dictionaryWithObjectsAndKeys:[NSString stringWithFormat:@"Get Food"], @"foodItem", nil] ;
   [[UIApplication sharedApplication] scheduleLocalNotification:localNotif];
    [localNotif release];

    Thanks in advance.

最佳答案

您应该使用NSCalendar和NSDateComponents进行数学运算-类似于：

NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* twoDaysAgo = [[NSDateComponents alloc] init];
twoDaysAgo.day = -2;
NSDate* dateToFire = [calendar dateByAddingComponents:twoDaysAgo toDate:date options:0];