【原】iOS學習之NSDate在項目中的一些類目擴充

在項目中，我們可能會面對各種各樣的對于時間的需求，在這裡提供幾種可能會用到的需求代碼

1、與今天的時間做比較，傳回日期內插補點

代碼：

- (NSInteger)compareWithToday {
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];

    NSDate *today = [NSDate date];    
    NSString *todayStr = [dateFormatter stringFromDate:today];
    today = [dateFormatter dateFromString:todayStr];
    
    NSInteger interval = (NSInteger) [self timeIntervalSinceDate:today];
    
    NSInteger intervalDate = 0;
    if (interval <= 0) {
        intervalDate = interval / (24 * 60 * 60) - 1;
    } else {
        intervalDate = interval / (24 * 60 * 60);
    }
    return intervalDate;
}      

2、距離目前的時間間隔描述

- (NSString *)timeIntervalDescription
{
    NSTimeInterval timeInterval = -[self timeIntervalSinceNow];
    if (timeInterval < 60) {
        return @"1分鐘内";
    } else if (timeInterval < 3600) {
        return [NSString stringWithFormat:@"%.f分鐘前", timeInterval / 60];
    } else if (timeInterval < 86400) {
        return [NSString stringWithFormat:@"%.f小時前", timeInterval / 3600];
    } else if (timeInterval < 2592000) {//30天内
        return [NSString stringWithFormat:@"%.f天前", timeInterval / 86400];
    } else if (timeInterval < 31536000) {//30天至1年内
        NSDateFormatter *dateFormatter = [NSDateFormatter dateFormatterWithFormat:@"M月d日"];
        return [dateFormatter stringFromDate:self];
    } else {
        return [NSString stringWithFormat:@"%.f年前", timeInterval / 31536000];
    }
}      

 該方法主要用于計算時間距離目前時間的時間間隔描述，主要使用時間戳進行比較。思路是先計算出時間戳與目前時間的時間戳的內插補點，然後進行比較。

3、分解時間

#define DATE_COMPONENTS (NSCalendarUnitYear| NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekOfYear |  NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond | NSCalendarUnitWeekday | NSCalendarUnitWeekdayOrdinal)
#define CURRENT_CALENDAR [NSCalendar currentCalendar]

- (NSInteger) nearestHour
{
    NSTimeInterval aTimeInterval = [[NSDate date] timeIntervalSinceReferenceDate] + D_MINUTE * 30;
    NSDate *newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
    NSDateComponents *components = [CURRENT_CALENDAR components:NSCalendarUnitHour fromDate:newDate];
    return components.hour;
}

- (NSInteger) hour
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.hour;
}

- (NSInteger) minute
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.minute;
}

- (NSInteger) seconds
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.second;
}

- (NSInteger) day
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.day;
}

- (NSInteger) month
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.month;
}

- (NSInteger) week
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.weekOfMonth;
}

- (NSInteger) weekday
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.weekday;
}

- (NSInteger) nthWeekday // e.g. 2nd Tuesday of the month is 2
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.weekdayOrdinal;
}

- (NSInteger) year
{
    NSDateComponents *components = [CURRENT_CALENDAR components:DATE_COMPONENTS fromDate:self];
    return components.year;
}      

 這些方法主要是用于将時間中某一個機關下的内容以數字的形式傳回。

 比如 2016-08-26 08:55:48 +0000 是零時區下的目前時間，

　　使用 - (NSInteger) year  方法的輸出結果就是 2016；

　　使用 - (NSInteger) hour  方法的輸出結果就是 目前時區的時間，我們在 8時區 ，結果就是 16；

　　使用 - (NSInteger) seconds  方法的輸出結果就是 48 ...