NetCore 依赖注入之服务之间的依赖关系

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简单介绍,直接官方文档

https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/dependency-injection?view=aspnetcore-2.2

public interface IOperation
{
Guid OperationId { get; }
}public interface IOperationTransient : IOperation
{
}public interface IOperationScoped : IOperation
{
}public interface IOperationSingleton : IOperation
{
}public interface IOperationSingletonInstance : IOperation
{
}

public class Operation : IOperationTransient,
IOperationScoped,
IOperationSingleton,
IOperationSingletonInstance
{
public Operation() : this(Guid.NewGuid())
{
} public Operation(Guid id)
{
OperationId = id;
} public Guid OperationId { get; private set; }
}

public class OperationService
{
public OperationService(
IOperationTransient transientOperation,
IOperationScoped scopedOperation,
IOperationSingleton singletonOperation,
IOperationSingletonInstance instanceOperation)
{
TransientOperation = transientOperation;
ScopedOperation = scopedOperation;
SingletonOperation = singletonOperation;
SingletonInstanceOperation = instanceOperation;
} public IOperationTransient TransientOperation { get; }
public IOperationScoped ScopedOperation { get; }
public IOperationSingleton SingletonOperation { get; }
public IOperationSingletonInstance SingletonInstanceOperation { get; }
}

在 Startup.ConfigureServices 中，根据其指定的生存期，将每个类型添加到容器中：
C#public void ConfigureServices(IServiceCollection services)
{
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2); services.AddScoped<IMyDependency, MyDependency>();
services.AddTransient<IOperationTransient, Operation>();
services.AddScoped<IOperationScoped, Operation>();
services.AddSingleton<IOperationSingleton, Operation>();
services.AddSingleton<IOperationSingletonInstance>(new Operation(Guid.Empty)); // OperationService depends on each of the other Operation types.
services.AddTransient<OperationService, OperationService>();
}

public class IndexModel : PageModel
{
private readonly IMyDependency _myDependency; public IndexModel(
IMyDependency myDependency,
OperationService operationService,
IOperationTransient transientOperation,
IOperationScoped scopedOperation,
IOperationSingleton singletonOperation,
IOperationSingletonInstance singletonInstanceOperation)
{
_myDependency = myDependency;
OperationService = operationService;
TransientOperation = transientOperation;
ScopedOperation = scopedOperation;
SingletonOperation = singletonOperation;
SingletonInstanceOperation = singletonInstanceOperation;
} public OperationService OperationService { get; }
public IOperationTransient TransientOperation { get; }
public IOperationScoped ScopedOperation { get; }
public IOperationSingleton SingletonOperation { get; }
public IOperationSingletonInstance SingletonInstanceOperation { get; } public async Task OnGetAsync()
{
await _myDependency.WriteMessage(
"IndexModel.OnGetAsync created this message.");
}
}

以下两个输出显示了两个请求的结果：

第一个请求：

控制器操作：

暂时性：d233e165-f417-469b-a866-1cf1935d2518
作用域：5d997e2d-55f5-4a64-8388-51c4e3a1ad19
单一实例：01271bc1-9e31-48e7-8f7c-7261b040ded9
实例：00000000-0000-0000-0000-000000000000

OperationService 操作：

暂时性：c6b049eb-1318-4e31-90f1-eb2dd849ff64
作用域：5d997e2d-55f5-4a64-8388-51c4e3a1ad19
单一实例：01271bc1-9e31-48e7-8f7c-7261b040ded9
实例：00000000-0000-0000-0000-000000000000

第二个请求：

控制器操作：

暂时性：b63bd538-0a37-4ff1-90ba-081c5138dda0
作用域：31e820c5-4834-4d22-83fc-a60118acb9f4
单一实例：01271bc1-9e31-48e7-8f7c-7261b040ded9
实例：00000000-0000-0000-0000-000000000000

OperationService 操作：

暂时性：c4cbacb8-36a2-436d-81c8-8c1b78808aaf
作用域：31e820c5-4834-4d22-83fc-a60118acb9f4
单一实例：01271bc1-9e31-48e7-8f7c-7261b040ded9
实例：00000000-0000-0000-0000-000000000000

观察哪个 OperationId 值会在一个请求之内和不同请求之间变化：

暂时性对象始终不同。第一个和第二个客户端请求的暂时性 OperationId 值对于 OperationService 操作和在客户端请求内都是不同的。为每个服务请求和客户端请求提供了一个新实例。
作用域对象在一个客户端请求中是相同的，但在多个客户端请求中是不同的。
单一实例对象对每个对象和每个请求都是相同的（不管 Startup.ConfigureServices 中是否提供 Operation 实例）。

接下来是本文重点要说明的

public void ConfigureServices(IServiceCollection services)
{ services.AddSingleton<SingletonService>(); services.AddTransient<TransientService>(); services.AddScoped<ScopedService>();
}

public class SingletonService
{
public string Id = Guid.NewGuid().ToString(); } public class ScopedService
{
public string Id = Guid.NewGuid().ToString(); } public class TransientService
{
public string Id = Guid.NewGuid().ToString(); private ScopedService _transient;
private SingletonService _singleton; public TransientService(ScopedService transient, SingletonService singleton)
{
_transient = transient;
_singleton = singleton;
} }这种情况是可以的,transient 可以依赖 singleton 和 scoped对于 Transient 服务,它可以被任何服务依赖,但是在依赖的服务中创建的服务的生命周期会跟随依赖的服务
对于 Scoped 服务,它只能被 Transient 和 Scoped 服务依赖,生命周期不会变化,如果要在 Singleton 服务中使用,可以使用 IServiceProvider 的 CreateScope 方法 ,然后 GetService, 但是生成的 scoped 服务生命周期为 Singleton

对于 Singleton 服务,它可以被任何服务依赖,生命周期不会变化

public class SingletonService
{
public string Id = Guid.NewGuid().ToString();
private ScopedService _scoped; public SingletonService(IServiceProvider serviceProvider)
{
using (var scope = serviceProvider.CreateScope())
{
_scoped = scope.ServiceProvider.GetService<ScopedService>();
}
}
} public class ScopedService
{
public string Id = Guid.NewGuid().ToString(); } public class TransientService
{
public string Id = Guid.NewGuid().ToString(); }

这个在单例中使用 Scoped 服务