Instance Sharing Example

This page provides a concrete example of how Singleton, Scoped, and Transient lifetimes behave in a hierarchical scope structure.

Scenario: LifetimeScope Hierarchy

Suppose you have the following LifetimeScope structure:

And a simple service with a unique ID:

public class MyService
{
    public Guid Id { get; } = Guid.NewGuid();
}

---

1. Singleton Registration

If MyService is registered as Singleton in the Root scope:

// RootLifetimeScope.cs
builder.Register<MyService>(Lifetime.Singleton);

Scope	MyService Instance (Id)	Note
Root	A	Created in Root
Scene1	A	Shared from Root
Popup1	A	Shared from Root
Popup2	A	Shared from Root
Scene2	A	Shared from Root

Behavior: All scopes share the same instance (A). Singleton creates one instance per registration, shared across the hierarchy.

---

2. Scoped Registration (in Root only)

If MyService is registered as Scoped in the Root scope:

// RootLifetimeScope.cs
builder.Register<MyService>(Lifetime.Scoped);

Scope	MyService Instance (Id)	Note
Root	A	Created in Root
Scene1	B	Created in Scene1
Popup1	C	Created in Popup1
Popup2	D	Created in Popup2
Scene2	E	Created in Scene2

Behavior:

• Lifetime.Scoped means "One instance per LifetimeScope".
• Even if registered in the Root, when a child scope (e.g., Scene1) resolves it, a new instance (B) is created and cached specifically for that child scope.
• Descendants (Popup1) also create their own instances (C) because they are separate scopes resolving a Scoped registration.

注記

If you want to share an instance across a specific subtree (e.g., Scene1 and its children), you should use Singleton registration within Scene1, or use RegisterInstance to pass a specific instance.

---

3. Scoped Registration (in Popup1 as well)

If MyService is registered as Scoped in Root, AND also in Popup1:

// RootLifetimeScope.cs
builder.Register<MyService>(Lifetime.Scoped);

// Popup1LifetimeScope.cs
builder.Register<MyService>(Lifetime.Scoped);

Scope	MyService Instance (Id)	Note
Root	A	Created in Root
Scene1	B	Created in Scene1
Popup1	F	Created in Popup1 (overridden)
Popup2	D	Created in Popup2 (uses Root registration)
Scene2	E	Created in Scene2

Behavior:

• Popup1 registers its own MyService, so it uses that registration. Since it is Scoped, it creates instance F.
• Popup2 does not have its own registration, so it uses the Root registration. Since it is Scoped, it creates instance D (separate from Scene1's instance).

---

4. Transient Registration (in Root)

If MyService is registered as Transient in the Root scope:

// RootLifetimeScope.cs
builder.Register<MyService>(Lifetime.Transient);

Scope	MyService Instance (Id)
Root	G (new every resolve)
Scene1	H (new every resolve)
Popup1	I (new every resolve)
Popup2	J (new every resolve)
Scene2	K (new every resolve)

Behavior: Every time the service is resolved, a new instance is created, regardless of the scope.

---

Summary Table

Lifetime	Instance Sharing Behavior
Singleton	One instance per registration. Shared across the hierarchy (Root and all descendants).
Scoped	One instance per LifetimeScope. Each scope (Parent, Child, etc.) gets its own unique instance when resolving.
Transient	New instance every time the service is resolved.