扩展NSDate类实现快捷使用 —— 昉

获取当前日期和时间：

+(NSDate *)getCurrentDate{
    NSDate *now = [NSDate date];
    return now;
}

将日期转换为字符串：

+(NSString *)getDateStringFromDate:(NSDate *)date{
    NSInteger location = 0;
    NSString *timeStr = @"";
    NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
    [formatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"] autorelease]];
    [formatter setDateFormat:@"HH:mm:a"];
    NSString *ampm = [[[formatter stringFromDate:date] componentsSeparatedByString:@":"] objectAtIndex:2];
    timeStr = [formatter stringFromDate:date];
    NSRange range = [timeStr rangeOfString:[NSString stringWithFormat:@":%@",ampm]];
    location = range.location;
    NSString *string = [timeStr substringToIndex:location];
    timeStr = [NSString stringWithFormat:@"%@ %@",ampm,string];
    NSString *dateStr = @"";
    NSDateFormatter *Dformatter = [[[NSDateFormatter alloc] init] autorelease];
    [Dformatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"] autorelease]];
    [Dformatter setDateFormat:@"yyyy-MM-dd"];    
    dateStr = [Dformatter stringFromDate:date];

    return [NSString stringWithFormat:@"%@  %@",dateStr,timeStr];
}

将字符串转换为日期：

+ (NSDate * )NSStringToNSDate: (NSString * )string
{    
    NSDateFormatter * formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"];
    NSDate *date = [formatter dateFromString :string];
    return date;
}

计算两个日期之间相差多少天：

+(NSInteger)getDateToDateDays:(NSDate *)date withSaveDate:(NSDate *)saveDate{
    NSCalendar* chineseClendar = [ [ NSCalendar alloc ] initWithCalendarIdentifier:NSGregorianCalendar ];  
    NSUInteger unitFlags =  NSHourCalendarUnit | NSMinuteCalendarUnit |   
    NSSecondCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit;  
    NSDateComponents *cps = [ chineseClendar components:unitFlags fromDate:date  toDate:saveDate  options:0];  
    NSInteger diffDay   = [ cps day ];  
    return diffDay;
}