为 NSDate 添加扩展类 判断时间

#import "NSDate+Extension.h"

@implementation NSDate (Extension)

/**
 *  判断某个时间是否为今年
 */
- (BOOL)isThisYear
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    // 获得某个时间的年月日时分秒
    NSDateComponents *dateCmps = [calendar components:NSCalendarUnitYear fromDate:self];
    NSDateComponents *nowCmps = [calendar components:NSCalendarUnitYear fromDate:[NSDate date]];
    return dateCmps.year == nowCmps.year;
}

/**
 *  判断某个时间是否为昨天
 */
- (BOOL)isYesterday
{
    NSDate *now = [NSDate date];
    
    // date ==  2014-04-30 10:05:28 --> 2014-04-30 00:00:00
    // now == 2014-05-01 09:22:10 --> 2014-05-01 00:00:00
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    fmt.dateFormat = @"yyyy-MM-dd";
    
    // 2014-04-30
    NSString *dateStr = [fmt stringFromDate:self];
    // 2014-10-18
    NSString *nowStr = [fmt stringFromDate:now];
    
    // 2014-10-30 00:00:00
    NSDate *date = [fmt dateFromString:dateStr];
    // 2014-10-18 00:00:00
    now = [fmt dateFromString:nowStr];
    
    NSCalendar *calendar = [NSCalendar currentCalendar];
    
    NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;
    NSDateComponents *cmps = [calendar components:unit fromDate:date toDate:now options:0];
    
    return cmps.year == 0 && cmps.month == 0 && cmps.day == 1;
}

/**
 *  判断某个时间是否为今天
 */
- (BOOL)isToday
{
    NSDate *now = [NSDate date];
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    fmt.dateFormat = @"yyyy-MM-dd";
    
    NSString *dateStr = [fmt stringFromDate:self];
    NSString *nowStr = [fmt stringFromDate:now];
    
    return [dateStr isEqualToString:nowStr];
}