在网上看到了一些ios中可能会常用的日期处理

//获取
当前月的下一月,上一月
- (void)setupRequestMonth
{
    NSDate *currentDate = [NSDate
date];
    NSDateFormatter *formatter = [[NSDateFormatter
alloc] init];
    [formatter setDateFormat:@"yyyy-MM"];
    
    NSCalendar *calendar = [[NSCalendar
alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *lastMonthComps = [[NSDateComponents
alloc] init];
    //    [lastMonthComps setYear:1]; // year = 1表示1年后的时间 year = -1为1年前的日期，month
day 类推
    [lastMonthComps setMonth:-1];
    NSDate *newdate = [calendar
dateByAddingComponents:lastMonthComps
toDate:currentDate options:0];
    NSString *dateStr = [formatter
stringFromDate:newdate];
    NSLog(@"date str = %@", dateStr);
}
//通过指定日期获取
当月 月初和月末的两天
- (NSArray *)getMonthFirstAndLastDayWith:(NSString *)dateStr{
    NSDateFormatter *format=[[NSDateFormatter
alloc] init];
    [format setDateFormat:@"YYYY-MM-dd hh:mm:ss"];
    NSDate *newDate=[format
dateFromString:dateStr];
    double interval =
0;
    NSDate *firstDate =
nil;
    NSDate *lastDate =
nil;
    NSCalendar *calendar = [NSCalendar
currentCalendar];
    
    BOOL OK = [calendar
rangeOfUnit:NSCalendarUnitMonth
startDate:& firstDate interval:&interval
forDate:newDate];
    
    if (OK) {
        lastDate = [firstDate
dateByAddingTimeInterval:interval -
1];
    }else {
        return
@[@"",@""];
    }
    
    NSDateFormatter *myDateFormatter = [[NSDateFormatter
alloc] init];
    [myDateFormatter setDateFormat:@"YYYY-MM-dd hh:mm:ss"];
    NSString *firstString = [myDateFormatter
stringFromDate: firstDate];
    NSString *lastString = [myDateFormatter
stringFromDate: lastDate];
    NSLog(@"first%@----PPPP",firstString);
    NSLog(@"last%@-----OOOOO",lastString);
    return
@[firstString, lastString];
}
//测试
相减一天的处理
- (BOOL)isSameNoDay:(NSDate*)date1 date2:(NSDate*)date2
{
    NSCalendar* calendar = [NSCalendar
currentCalendar];
    
    unsigned unitFlags =
NSYearCalendarUnit | NSMonthCalendarUnit | 
NSDayCalendarUnit;
    NSDateComponents* comp1 = [calendar
components:unitFlags fromDate:date1];
    NSDateComponents* comp2 = [calendar
components:unitFlags fromDate:date2];
    return [comp1
day]+1
  == [comp2 day] &&
    [comp1 month] == [comp2
month] &&
    [comp1 year] 
== [comp2 year];
}
//获取日期的字符串
-(NSStrin
b0ee
g*)getDataStr{
    NSDate *date = [NSDate
date];
    NSDateFormatter *formatter = [[NSDateFormatter
alloc] init];
    [formatter setDateStyle:NSDateFormatterMediumStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    [formatter setDateFormat:@"YYYY-MM-dd hh:mm:ss"];
    return [formatter
stringFromDate:date];
}
//获取指定日期的字符串
-(NSString*)getDataStrByDate:(NSDate*)date{
    NSDateFormatter *formatter = [[NSDateFormatter
alloc] init];
    [formatter setDateStyle:NSDateFormatterMediumStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    [formatter setDateFormat:@"YYYY-MM-dd hh:mm:ss"];
    return [formatter
stringFromDate:date];
}
//获取当前日期
-(NSDate*)getData{
    NSDate *date = [NSDate
date];
    NSDateFormatter *formatter = [[NSDateFormatter
alloc] init];
    [formatter setDateStyle:NSDateFormatterMediumStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    [formatter setDateFormat:@"YYYY-MM-dd hh:mm:ss"];
    return date;
}