Tips for injecting a service into a class (not a component)

Question

Tips for injecting a service into a class (not a component)

Can you inject a service into a class that is not a component?

Consider the following scenario:

Myservice

import {Injectable} from '@angular/core';
@Injectable()
export class myService {
  dosomething() {
    // implementation
  }
}

MyClass

import { myService } from './myService'
export class MyClass {
  constructor(private myservice:myService) {

  }
  test() {
     this.myservice.dosomething();
  }
}

I attempted to do so, but it didn't work. It appears that services should only be used in components or other services.

Is there a way to utilize a service in a regular class? Or is it considered bad practice to do so?

Thank you for your insights.

angular typescript

Answer 1

Answer №1

When dealing with injections, it is important to note that they only work with classes that are instantiated by Angular's dependency injection (DI).

To properly utilize injections, make sure to:

Include @Injectable() in the definition of MyClass and
Specify MyClass in the providers array like providers: [MyClass] within a component or NgModule.

By following these steps, when you inject MyClass, an instance of MyService will be passed to it during instantiation via DI.

Another approach is to set up a custom injector as follows:

Using the updated static injector:

constructor(private injector:Injector) { 
  let childInjector = Injector.create({ providers: [MyClass], parent: this.injector});

  let myClass : MyClass = childInjector.get(MyClass);
}

Utilizing the deprecated ReflectiveInjector:

constructor(private injector:Injector) { 
  let resolvedProviders = ReflectiveInjector.resolve([MyClass]);
  let childInjector = ReflectiveInjector.fromResolvedProviders(resolvedProviders, this.injector);

  let myClass : MyClass = childInjector.get(MyClass);
}

This method ensures that myClass will be an instance of MyClass created by Angular's DI, with myService injected into it upon instantiation.
For more information, refer to Getting dependency from Injector manually inside a directive

Alternatively, you can manually create the instance yourself:

constructor(ms:myService)
let myClass = new MyClass(ms);

Answer 2

When dealing with injections, it is important to note that they only work with classes that are instantiated by Angular's dependency injection (DI).

To properly utilize injections, make sure to:

Include @Injectable() in the definition of MyClass and
Specify MyClass in the providers array like providers: [MyClass] within a component or NgModule.

By following these steps, when you inject MyClass, an instance of MyService will be passed to it during instantiation via DI.

Another approach is to set up a custom injector as follows:

Using the updated static injector:

constructor(private injector:Injector) { 
  let childInjector = Injector.create({ providers: [MyClass], parent: this.injector});

  let myClass : MyClass = childInjector.get(MyClass);
}

Utilizing the deprecated ReflectiveInjector:

constructor(private injector:Injector) { 
  let resolvedProviders = ReflectiveInjector.resolve([MyClass]);
  let childInjector = ReflectiveInjector.fromResolvedProviders(resolvedProviders, this.injector);

  let myClass : MyClass = childInjector.get(MyClass);
}

This method ensures that myClass will be an instance of MyClass created by Angular's DI, with myService injected into it upon instantiation.
For more information, refer to Getting dependency from Injector manually inside a directive

Alternatively, you can manually create the instance yourself:

constructor(ms:myService)
let myClass = new MyClass(ms);

Answer 3

Answer №2

If you happen to come across this while browsing through SO for the same reason I am, maybe this can offer some insight...

Imagine you are utilizing ng2-translate and you wish to integrate it into your User.ts class. Initially, the instinct might be to employ dependency injection since Angular is in play here. However, a simpler approach could involve passing it through the constructor or even setting it as a public variable within the component where it was injected (presumably).

For instance:

import { TranslateService } from "ng2-translate";

export class User {
  public translateService: TranslateService; // to be set from components.

  // various User methods go here
}

Subsequently, in a user-related component that has Injected TranslateService:

addEmptyUser() {
  let emptyUser = new User("", "");
  emptyUser.translateService = this.translateService;
  this.users.push(emptyUser);
}

This explanation may assist individuals like myself who were on the verge of coding intricate solutions when sometimes simplicity suffices =]

(NOTE: opting to set a variable instead of including it in the constructor method allows flexibility for scenarios where the service may not always be necessary. Being obligated to pass it in each time could result in unnecessary imports/code that remain unused.)

Answer 4

If you happen to come across this while browsing through SO for the same reason I am, maybe this can offer some insight...

Imagine you are utilizing ng2-translate and you wish to integrate it into your User.ts class. Initially, the instinct might be to employ dependency injection since Angular is in play here. However, a simpler approach could involve passing it through the constructor or even setting it as a public variable within the component where it was injected (presumably).

For instance:

import { TranslateService } from "ng2-translate";

export class User {
  public translateService: TranslateService; // to be set from components.

  // various User methods go here
}

Subsequently, in a user-related component that has Injected TranslateService:

addEmptyUser() {
  let emptyUser = new User("", "");
  emptyUser.translateService = this.translateService;
  this.users.push(emptyUser);
}

This explanation may assist individuals like myself who were on the verge of coding intricate solutions when sometimes simplicity suffices =]

(NOTE: opting to set a variable instead of including it in the constructor method allows flexibility for scenarios where the service may not always be necessary. Being obligated to pass it in each time could result in unnecessary imports/code that remain unused.)

Answer 5

Answer №3

Here's a little hacky solution that I came up with and wanted to share. Keep in mind, this method will only be effective with Singleton services (these are injected at the app root, not within components). Singleton services persist for the duration of your application and there is only one instance of them.

First, define your service like this:

@Injectable()
export class MyService {
    static instance: MyService;
    constructor() {
        MyService.instance = this;
    }

    doSomething() {
        console.log("something!");
    }
}

Now, you can use this service in any class:

export class MyClass {
    constructor() {
        MyService.instance.doSomething();
    }
}

This approach can help streamline your code and is handy if you don't require non-singleton services.

Answer 6

Here's a little hacky solution that I came up with and wanted to share. Keep in mind, this method will only be effective with Singleton services (these are injected at the app root, not within components). Singleton services persist for the duration of your application and there is only one instance of them.

First, define your service like this:

@Injectable()
export class MyService {
    static instance: MyService;
    constructor() {
        MyService.instance = this;
    }

    doSomething() {
        console.log("something!");
    }
}

Now, you can use this service in any class:

export class MyClass {
    constructor() {
        MyService.instance.doSomething();
    }
}

This approach can help streamline your code and is handy if you don't require non-singleton services.

Answer 7

Answer №4

ServiceLocator for Angular

import {Injector} from "@angular/core";

export class ServiceLocator {
    static injector: Injector;
}

Setting up AppModule

@NgModule({ ... })

export class AppModule {
    constructor(private injector: Injector) {
        ServiceLocator.injector = injector;
    }
 }

Poney Model with Service Injection

export class Poney {

    id: number;
    name: string;
    color: 'black' | 'white' | 'brown';

    service: PoneyService = ServiceLocator.injector.get(PoneyService); // <--- Ensuring correct service injection

    // PoneyService is @injectable and registered in app.module.ts
}

Answer 8

ServiceLocator for Angular

import {Injector} from "@angular/core";

export class ServiceLocator {
    static injector: Injector;
}

Setting up AppModule

@NgModule({ ... })

export class AppModule {
    constructor(private injector: Injector) {
        ServiceLocator.injector = injector;
    }
 }

Poney Model with Service Injection

export class Poney {

    id: number;
    name: string;
    color: 'black' | 'white' | 'brown';

    service: PoneyService = ServiceLocator.injector.get(PoneyService); // <--- Ensuring correct service injection

    // PoneyService is @injectable and registered in app.module.ts
}

Answer 9

Answer №5

Since the release of Angular 14, developers have had access to the inject function. It's important to note that this function should only be called within the constructor.

import { MyService } from './my.service'
export class MyClass {
  private myService = inject(MyService);

  test() {
     this.myservice.dosomething();
  }
}

In a different context:

import { MyClass } from './myClass'
@component()
export class MyComponent {
  constructor() {
    const myClass = new MyClass();
  }
}

Answer 10

Since the release of Angular 14, developers have had access to the inject function. It's important to note that this function should only be called within the constructor.

import { MyService } from './my.service'
export class MyClass {
  private myService = inject(MyService);

  test() {
     this.myservice.dosomething();
  }
}

In a different context:

import { MyClass } from './myClass'
@component()
export class MyComponent {
  constructor() {
    const myClass = new MyClass();
  }
}

Answer 11

Answer №6

If your functions within a service are pure, one approach to resolve this issue is by utilizing static members within the service.

Example of a Service

import {Injectable} from '@angular/core';
@Injectable()
export class myService{
  public static dosomething(){
    //implementation => no need for `this` keyword
  }
}

Example of a Class

export class MyClass{
  test(){
     MyService.dosomething(); //directly access without constructor injection
  }
}

Answer 12

If your functions within a service are pure, one approach to resolve this issue is by utilizing static members within the service.

Example of a Service

import {Injectable} from '@angular/core';
@Injectable()
export class myService{
  public static dosomething(){
    //implementation => no need for `this` keyword
  }
}

Example of a Class

export class MyClass{
  test(){
     MyService.dosomething(); //directly access without constructor injection
  }
}

Answer 13

Answer №7

One way to streamline your code is by utilizing a factory pattern, such as the MyClassFactory:

import { Injectable } from '@angular/core';
@Injectable()
export class MyService {
  dosomething() {
    // implementation
  }
}

import { Injectable } from '@angular/core';
import { MyService } from './MyService'

@Injectable()
export class MyClassFactory {
  constructor(private myService:MyService) { }

  createMyClass() {
    return new MyClass(this.myService)
  }
}

import { MyService } from './MyService'
export class MyClass {
  constructor(private myService:MyService) { }
  test() {
     this.myservice.dosomething();
  }
}

Answer 14

One way to streamline your code is by utilizing a factory pattern, such as the MyClassFactory:

import { Injectable } from '@angular/core';
@Injectable()
export class MyService {
  dosomething() {
    // implementation
  }
}

import { Injectable } from '@angular/core';
import { MyService } from './MyService'

@Injectable()
export class MyClassFactory {
  constructor(private myService:MyService) { }

  createMyClass() {
    return new MyClass(this.myService)
  }
}

import { MyService } from './MyService'
export class MyClass {
  constructor(private myService:MyService) { }
  test() {
     this.myservice.dosomething();
  }
}

Tips for injecting a service into a class (not a component)

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

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