创建日程时对时间的判断（通过计算时间差进行判断NSTimeInterval）

    NSDate *date = [NSDate date];

    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];

    [dateFormat setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    //获得系统当前日期

    NSString *dString = [dateFormat stringFromDate:date];

    NSDate *currentDate = [dateFormat dateFromString:dString];

    //开始时间

    NSString *startTime = self.startTime.text;

    NSDate *startDate = [dateFormat dateFromString:startTime];

    //结束时间

    NSString *endTime = self.endTime.text;

    NSDate *endData = [dateFormat dateFromString:endTime];

    //计算时间间隔

    NSTimeInterval secondsBetweenCurrentDateToStartDate = [currentDate timeIntervalSinceDate:startDate];

    NSTimeInterval secondsBetweenCurrentDateToEndDate = [currentDate timeIntervalSinceDate:endData];

    NSTimeInterval secondsBetweenStartToEndDate = [startDate timeIntervalSinceDate: endData];

    //判断时间

    if (secondsBetweenCurrentDateToStartDate > 0.000000) {

        [SettingData alert:@"开始时间不能晚于当前时间!" delegeate:nil];

        return;

    }

    if (secondsBetweenCurrentDateToEndDate > 0.000000) {

        [SettingData alert:@"结束时间不能晚于当前时间!" delegeate:nil];

        return;

    }

    if (secondsBetweenStartToEndDate >0.000000) {

        [SettingData alert:@"开始时间不能晚于结束时间!" delegeate:nil];

        return;

    }