一.服務的生存期
在容器中每個註冊的服務,根據程序應用需求都可以選擇合適的服務生存期,ASP.NET Core 服務有三種生存期配置:
(1) Transient:暫時生存期,在每次請求時被創建。 這種生存期適合輕量級的,無狀態的服務。
(2) Scoped: 作用域生存期,在每次請求被創建一次。
(3) Singleton: 單例生存期,在它們第一次被請求時創建。每個後續請求將使用相同的實例。如果應用程序需要單例行為,建議讓服務容器管理服務的生命週期,而不是在自己的類中實現單例模式。
1.1 演示案例
為了演示生存期和註冊選項之間的差異, 以下服務接口,任務是演示標識符 OperationId 的操作值變化。 根據為以下接口配置操作服務的生存期的方式,容器在類請求時提供相同或不同的服務實例:
<code>public
interface
IOperation
{ Guid OperationId {get
; } }public
interface
IOperationTransient
:IOperation
{ }public
interface
IOperationScoped
:IOperation
{ }public
interface
IOperationSingleton
:IOperation
{ }public
interface
IOperationSingletonInstance
:IOperation
{ }/<code>
上面四種服務接口在 Operation 類中實現。 調用 Operation類時將自動生成一個 GUID(如果實例化Operation類時沒有指定GUID),下面是Operation類的實現:
<code>public
class
Operation
:IOperationTransient
,IOperationScoped
,IOperationSingleton
,IOperationSingletonInstance
{public
Operation
() :this
(Guid.NewGuid(
)) { }public
Operation
(Guid id
) { OperationId = id; }public
Guid OperationId {get
;private
set
; } }/<code>
再註冊一個 OperationService 服務,該服務取決於每個其他 Operation 類型。 當通過依賴關係注入請求 OperationService 時,它將接收每個服務的新實例或基於從屬服務(Operation )的生存期的現有實例。OperationService 服務作用就是第二次調用 Operation類,查看Operation類實例的作用域變化。
<code>public
class OperationService
{
public
IOperationTransient TransientOperation { get; }
public
IOperationScoped ScopedOperation { get; }
public
IOperationSingleton SingletonOperation { get; }
public
IOperationSingletonInstance SingletonInstanceOperation { get; }
public
OperationService(
IOperationTransient
transientOperation,
IOperationScoped
scopedOperation,
IOperationSingleton
singletonOperation,
IOperationSingletonInstance
instanceOperation)
{
TransientOperation
=transientOperation;
ScopedOperation
=scopedOperation;
SingletonOperation
=singletonOperation;
SingletonInstanceOperation
=instanceOperation;
}
}
/<code>
(1) 如果在請求時創建了臨時服務(Transient),則 IOperationTransient 服務的 OperationId 與 OperationService 的 OperationId 不同。 OperationService 將接收 IOperationTransient 類的新實例。 新實例將生成一個不同的 OperationId。
(2) 如果按請求創建有作用域的服務(Scoped),則 IOperationScoped 服務的 OperationId 與請求中 OperationService 的該 ID 相同。 在請求中,兩個服務共享不同的 OperationId 值。
(3) 如果單一實例服務(Singleton),則只創建一次 並在所有請求和所有服務中使用,則 OperationId 在所有服務請求中保持不變。
下面是在 Startup.ConfigureServices 服務容器中註冊,指定服務的生存期:
<code>services
.AddTransient
<IOperationTransient
,Operation
>();services
.AddScoped
<IOperationScoped
,Operation
>();services
.AddSingleton
<IOperationSingleton
,Operation
>();services
.AddSingleton
<IOperationSingletonInstance
>(new
Operation
(Guid
.Empty
));services
.AddTransient
<OperationService
,OperationService
>();/<code>
為了演示各個請求中的對象生存期。 下面示例應用 Index頁面,請求 IOperation 類型和 OperationService。 然後查看Operation類屬性OperationId 值的變化:
<code>public
class
IndexModel
:PageModel
{public
OperationService OperationService {get
; }public
IOperationTransient TransientOperation {get
; }public
IOperationScoped ScopedOperation {get
; }public
IOperationSingleton SingletonOperation {get
; }public
IOperationSingletonInstance SingletonInstanceOperation {get
; }public
IndexModel
(OperationService operationService, IOperationTransient transientOperation, IOperationScoped scopedOperation, IOperationSingleton singletonOperation, IOperationSingletonInstance singletonInstanceOperation
) { OperationService = operationService; TransientOperation = transientOperation; ScopedOperation = scopedOperation; SingletonOperation = singletonOperation; SingletonInstanceOperation = singletonInstanceOperation; }public
string
BindGUIDMsg {get
;set
; }public
void
OnGet
() { BindGUIDMsg +="IOperation操作:
; BindGUIDMsg +=
""暫時性:"
+ TransientOperation.OperationId.ToString() +""
; BindGUIDMsg +="有作用域:"
+ ScopedOperation.OperationId.ToString() +""
; BindGUIDMsg +="單一實例:"
+ SingletonOperation.OperationId.ToString() +""
; BindGUIDMsg +="實例:"
+ SingletonInstanceOperation.OperationId.ToString() +""
; BindGUIDMsg +="OperationService操作:"
; BindGUIDMsg +="暫時性:"
+ OperationService.TransientOperation.OperationId.ToString() +""
; BindGUIDMsg +="有作用域:"
+ OperationService.ScopedOperation.OperationId.ToString() +""
; BindGUIDMsg +="單一實例:"
+ OperationService.SingletonOperation.OperationId.ToString() +""
; BindGUIDMsg +="實例:"
+ OperationService.SingletonInstanceOperation.OperationId.ToString() +""
; } }/<code>
<code>@{ @Html.Raw(@Model.BindGUIDMsg); }
/<code>
第一次Index頁面請求:
IOperation 操作: 暫時性:
8ef874a3-743d-4288-98d4-3df126cd940d 有作用域:
256ff050-f469-4ea3-8dde-16cdd3087c83 單一實例:
d2caf297-a9b1-4dcf-ADDA-c68e46fe0741 實例:00000000-0000-0000-0000 -000000000000 OperationService操作: 暫時性:
5411fd0d-f2e1-4885-beee-2d7ccf48dceb 有作用域:
256ff050-f469-4ea3-8dde-16cdd3087c83 單一實例:
d2caf297-a9b1-4dcf-adda-c68e46fe0741 實例:00000000-0000-0000- 0000-000000000000
第二次Index頁面請求:
IOperation操作: 暫時性
:e685fd0e-d2e0-4900-9eff-e6bc41cd2f80 有作用域
:ca233b49-8326-4a7e-8ee4-6993d70786ed 單一實例
:d2caf297-a9b1-4dcf-adda-c68e46fe0741 實例
:00000000-0000-0000-0000-000000000000 OperationService操作: 暫時性
:db89be00-c3b7-4f99-bead-5be693ccc2c0 有作用域
:ca233b49-8326-4a7e-8ee4-6993d70786ed 單一實例
:d2caf297-a9b1-4dcf-adda-c68e46fe0741 實例
:00000000-0000-0000-0000-000000000000
下面再總結一下:
(1)暫時性註冊的服務,每次調用服務都會是一個新的服務對象實例。相當於在IndexModel類的局部(方法或屬性中)實例化一個依賴對象Operation類,偽代碼是:
<code>public
class
IndexModel
{public
void
OnGet
()
{ OperationService operationService=new
OperationService(); IOperationTransient TransientOperation =new
Operation(); } }/<code>
(2)作用域註冊的服務,一次請求內(加載一次index頁)對象實例是相同的,但每次請求會產生一個新實例。相當於在IndexModel類的全局中實例化一次依賴對象Operation類,偽代碼是:
<code> OperationService operationService =null
;public
IndexModel
() { operationService =new
OperationService(); operationService.ScopedOperation =new
Operation(); }public
void
OnGet
() { operationService.ScopedOperation.OperationId; IOperationScoped operationScoped=operationService.ScopedOperation; operationScoped.OperationId }/<code>
(3)單例註冊的服務,實例對象對每個對象和每個請求都是相同的。相當於在整個應用Application中只實例化一次,常見的單例模式。