ABP框架系列之五十一：(Timing-定时)
Introduction
While some applications target a single timezone, some others target to many different timezones. To satisfy such needs and centralize datetime operations, Abp provides common infrastructure for datetime operations.
一些应用目标一个时区，另一些目标的许多不同的时区。为了满足这种需要，集中时间操作，abp提供了日期时间操作的公共基础。
Clock
Clock is the main class used to work with DateTime values. It defines the following static properties/methods:
- Now: Gets current time according to current provider.（根据当前提供程序获取当前时间）
- Kind: Gets DateTimeKind of current provider.（根据当前提供程序获取当前时间类型）
- SupportsMultipleTimezone: Gets a value indicates that current provider can be used for applications need to multiple timezones.（获取一个值，表明当前提供程序可以使用的应用程序需要多个时区）
- Normalize: Normalizes/converts given DateTime upon current provider（转换给定的时间为当前提供程序的时间）.
So, instead of using DateTime.Now, we are using Clock.Now, which abstracts it:
DateTime now = Clock.Now;
Clock uses clock providers inside it. There are three types of built-in clock providers:（有三种类型的内置时钟提供程序）
- ClockProviders.Unspecified (UnspecifiedClockProvider):（未指定） This is the default clock provider and behaives just like DateTime.Now. It acts as you don't use Clock class at all.
- ClockProviders.Utc (UtcClockProvider): Works in UTC datetime. DateTime.UtcNow for Clock.Now. Normalize method converts a given datetime to utc datetime and set it's kind to DateTimeKind.UTC. It supports multiple timezones.
- ClockProviders.Local (LocalClockProvider): Works in Local computer's time. Normalize method converts a given datetime to local datetime and set it's kind to DateTimeKind.Local.
You can set Clock.Provider in order to use a different clock provider:
Clock.Provider = ClockProviders.Utc;
This is generally done at the beginning of an application (proper to do it Application_Start in a web application).
Client Side
Clock can be used on the client side by abp.clock object in javascript. When you set Clock.Provider on the server side, ABP automatically sets value of abp.clock.provider on the client side.
Time Zones
ABP defines a setting named Abp.Timing.TimeZone (TimingSettingNames.TimeZone constant) for storing selected timezone of host, tenant and user. ABP assumes that value of timezone setting is a valid Windows timezone name. It also defines a timezone mapping file to convert a Windows Timezone to IANA timezone since some of the common libraries are using IANA timezone id. UtcClockProvider must be used in order to support multiple timezones. Because if UtcClockProvider is used, all datetime values will be stored in UTC and all datetimes will be sent to clients in UTC format. Then on the client side we can convert UTC datetime to user's timezone by using user's current timezone setting.
ABP定义设置命名为Abp.Timing.TimeZone（timingsettingnames.timezone常数）储存宿主选择时区，租户和用户。ABP假定时区设置值是否是有效的Windows时区名称。它还定义了一个时区映射文件转换为Windows时区时区以来对IANA的一些常见的图书馆使用IANA时区ID。utcclockprovider必须为了支持多时区。因为如果utcclockprovider使用，所有日期时间值将被存储在UTC和所有日期将被送往UTC格式的客户。然后在客户端我们可以将UTCDateTime用户的时区使用用户的当前时区设置。
Client Side
ABP creates an javascript object named abp.timing.timeZoneInfo which contains timezone information for current user. This information contains Windows and IANA timezone ids and some extra information for windows timezone info. This information can be used to make client side datetime convertions and showing a datetime to user in his/her timezone.
Binders and Converters（粘合剂和转换器）
- ABP automatically normalizes DateTimes received from clients in MVC, Web API and ASP.NET Core applications, based on the current clock provider.
- ABP automatically normalized DateTimes received from database based on the current clock provider, when EntityFramework or NHibernate modules used.
If UTC clock provider is used, then all DateTimes stored in database assumed as UTC values, and all DateTimes received from clients assumed as UTC unless it's explicitly specified.
