每天重复的本地通知-iOS

我每天都在后台使用定位服务更新我的应用程序。在后台，它解析XML并将本地通知设置为18小时，但仅当解析的数据不同时，才显示“无警告”。但我每天都收到同样的通知，即使我不应该这样做。这就是我推送通知的方式

If(![self.city isEqualToString:@"No warning"]){

// We only need 1 notification 
[[UIApplication sharedApplication] cancelAllLocalNotifications];

 NSCalendar *gregCalendar = [[NSCalendar alloc]initWithCalendarIdentifier:NSGregorianCalendar];

                NSDateComponents *dateComponents = [gregCalendar components: NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit fromDate:[NSDate date]];

                [dateComponents setYear:[dateComponents year]];
                [dateComponents setMonth:[dateComponents month]];
                [dateComponents setDay:[dateComponents day]];
                [dateComponents setHour:18];
                [dateComponents setMinute:0];



                UIDatePicker *dd = [[UIDatePicker alloc]init];
                [dd setDate:[gregCalendar dateFromComponents:dateComponents]];

                UILocalNotification *notification = [[UILocalNotification alloc]init];
                notification.alertBody = [NSString stringWithFormat:@"%@ %@",self.date,self.city];
                notification.soundName = UILocalNotificationDefaultSoundName;
                notification.repeatInterval = 0;
                [notification setFireDate:dd.date];
                [notification setTimeZone:[NSTimeZone  defaultTimeZone]];
                [[UIApplication sharedApplication] scheduleLocalNotification:notification];

}

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你准备好了吗？城市？我已经解决了这个问题解决方案是什么？