113. Understanding the Hierarchical Injector

Jul 15, 2026 04:41 · 2:41 · English · Whisper Turbo · 1 කථානායක

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

In the last lecture we set up our account service and hooked it up in our app

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

and still our app seems to be broken.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

If I click these buttons the status is not changed.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

So somehow our code is not working.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

Actually it's working correctly.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

We're just using services wrong here.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

In this specific case we're not using the service in the way we should

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

use it in our app.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

What's going wrong?

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

the Angular dependency injector actually is

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

a hierarchical injector.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

That means that if we provide a service in

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

some place of our app,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

let's say on one component,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

the Angular framework knows how to create

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

an instance of that service for this component and,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

important, all its child components.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

And actually,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

this component

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

and all its child components and the child components of the child components

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

will receive the same instance of this service.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

There are other places where we can provide a service too.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

The highest possible level is the app module.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

We haven't done this yet,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

but we will see this soon.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

If we provide a service there,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

The app module does have a provider's array.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

The same instance,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

and that's important,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

the same instance of the class of the service is

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

available in our whole app,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

in all components,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

in all directives,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

in all other services where we maybe inject a service.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

Yes, we can inject services into services.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

I'll come back to this.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

The next level,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

for example,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

would be the app component.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

There,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

the app component and all its child components do have

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

the same instance of the service.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

And this is true for any component.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

So even if we have a child of the app component,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

if we provide it on that child,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

all the children of this child will have the same instance and the child

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

itself, but not the app component.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

The instances don't propagate up.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

They only go down that tree of components.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

The lowest level,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

therefore, is a single component with no child components.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

If we provide a service there,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

this component will have its own instance of the service,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

and,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

well, it doesn't have any child components,

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

so this instance will only be available for this component.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

And this will actually even overwrite if we were to provide

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

the same service on a higher level.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

And that's exactly what we're doing.

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S… Speaker 1 (113. Understanding the Hierarchical Injector)

So let's take a closer look in the next lecture.

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