Tips for refreshing the value of a dependency injection token

Question

Tips for refreshing the value of a dependency injection token

When using Angular dependency injection, you have the ability to inject a string, function, or object by using a token instead of a service class.

To declare it in my module, I do this:

providers: [{ provide: MyValueToken, useValue: 'my title value'}]

and then I can use it like this:

constructor(@Inject(MyValueToken) my_value: string) {
  this.title = my_value;
}

But how can I update the value from the component and have other components always receive the new value? Essentially, I want to mimic the functionality of a BehaviorSubject to emit and receive values.

If achieving this is not possible, then what is the purpose of these injection tokens providing static data, when I could simply declare the static value in my component and use it directly?

angular typescript angular-services angular-decorator angular-di

Answer 1

Answer №1

Instead of using an immutable primitive, consider utilizing a BehaviorSubject, allowing you to access and update it in one component while subscribing in another:

export const VALUE_TOKEN = new InjectionToken<BehaviorSubject<string>>('value.token')

providers: [{ provide: VALUE_TOKEN, useValue: new BehaviorSubject('')}]
    
// subscriber
constructor(@Inject(VALUE_TOKEN) value: BehaviorSubject<string>) {
  value.subscribe((value)=>this.message = value);
}

// publisher
constructor(@Inject(VALUE_TOKEN) value: BehaviorSubject<string>) {
  value.next('updated message');
}

Answer 2

Instead of using an immutable primitive, consider utilizing a BehaviorSubject, allowing you to access and update it in one component while subscribing in another:

export const VALUE_TOKEN = new InjectionToken<BehaviorSubject<string>>('value.token')

providers: [{ provide: VALUE_TOKEN, useValue: new BehaviorSubject('')}]
    
// subscriber
constructor(@Inject(VALUE_TOKEN) value: BehaviorSubject<string>) {
  value.subscribe((value)=>this.message = value);
}

// publisher
constructor(@Inject(VALUE_TOKEN) value: BehaviorSubject<string>) {
  value.next('updated message');
}

Answer 3

Answer №2

If you find yourself in a situation where each consumer requires its own instance of BehaviourSubject, it is recommended to define a factory function to handle this specific use-case.

Here's an example:

const myFactory = () => { return new BehaviorSubject<string>('') };

providers: [
    { provide: MyValueToken, useFactory: myFactory }
]

// Consumer
constructor(@Inject(MyValueToken) my_value: BehaviorSubject) {
  my_value.subscribe((my_value)=>this.title = my_value);
}

// Producer
constructor(@Inject(MyValueToken) my_value: BehaviorSubject) {
  my_value.next('my title value');
}

Answer 4

If you find yourself in a situation where each consumer requires its own instance of BehaviourSubject, it is recommended to define a factory function to handle this specific use-case.

Here's an example:

const myFactory = () => { return new BehaviorSubject<string>('') };

providers: [
    { provide: MyValueToken, useFactory: myFactory }
]

// Consumer
constructor(@Inject(MyValueToken) my_value: BehaviorSubject) {
  my_value.subscribe((my_value)=>this.title = my_value);
}

// Producer
constructor(@Inject(MyValueToken) my_value: BehaviorSubject) {
  my_value.next('my title value');
}

Answer 5

Answer №3

If you prefer not to utilize a BehaviorSubject, an alternative approach is to create a simple class with getter and setter methods.

class MyData {

  get data(): string {
    return this._data;   
  }

  set data(val: string) {
   this._data = val;
  }
  private _data = '';

}

const MY_DATA_TOKEN = new InjectionToken<MyData>('MY_DATA_TOKEN ');

// Include the class in either the module or component providers array.
providers: [
  { provide: MY_DATA_TOKEN , useClass: MyData },
]

class MyApplication {

  // Inject the class in the component constructor
  constructor(
    @Inject(MY_DATA_TOKEN) private _myData: MyData,
  ) {

    // Access the current value
    console.log(this._myData.data);

    // Set a new value
    this._myData.data = 'new data';
  }

}

Answer 6

If you prefer not to utilize a BehaviorSubject, an alternative approach is to create a simple class with getter and setter methods.

class MyData {

  get data(): string {
    return this._data;   
  }

  set data(val: string) {
   this._data = val;
  }
  private _data = '';

}

const MY_DATA_TOKEN = new InjectionToken<MyData>('MY_DATA_TOKEN ');

// Include the class in either the module or component providers array.
providers: [
  { provide: MY_DATA_TOKEN , useClass: MyData },
]

class MyApplication {

  // Inject the class in the component constructor
  constructor(
    @Inject(MY_DATA_TOKEN) private _myData: MyData,
  ) {

    // Access the current value
    console.log(this._myData.data);

    // Set a new value
    this._myData.data = 'new data';
  }

}

Answer 7

Answer №4

Explaining the Reason Why...

If you've ever wondered why injecting a static structure is important, Angular Material frequently uses this method to configure components.

For example, with the Chips control:

@NgModule({
  providers: [
    {
      provide: MAT_CHIPS_DEFAULT_OPTIONS,
      useValue: {
        separatorKeyCodes: [ENTER, COMMA]
      }
    }
  ]
})

You don't necessarily need to fully understand the data being provided, just know that you're injecting a token MAT_CHIPS_DEFAULT_OPTIONS with value

{ separatorKeyCodes: [ENTER, COMMA] }

This configuration will be inherited either from your AppModule or from any other module or component where it's defined - similar to how injectable services work. It can also be applied directly within a @Component or @Directive for specific component settings.

If a different part of your application requires different configuration, you simply inject it there and only the relevant components will inherit those changes.

While it may seem cumbersome compared to setting values directly on a component, this approach is common for many Angular Material controls. The advantage lies in setting it once and allowing everything to inherit the configuration.

Answer 8

Explaining the Reason Why...

If you've ever wondered why injecting a static structure is important, Angular Material frequently uses this method to configure components.

For example, with the Chips control:

@NgModule({
  providers: [
    {
      provide: MAT_CHIPS_DEFAULT_OPTIONS,
      useValue: {
        separatorKeyCodes: [ENTER, COMMA]
      }
    }
  ]
})

You don't necessarily need to fully understand the data being provided, just know that you're injecting a token MAT_CHIPS_DEFAULT_OPTIONS with value

{ separatorKeyCodes: [ENTER, COMMA] }

This configuration will be inherited either from your AppModule or from any other module or component where it's defined - similar to how injectable services work. It can also be applied directly within a @Component or @Directive for specific component settings.

If a different part of your application requires different configuration, you simply inject it there and only the relevant components will inherit those changes.

While it may seem cumbersome compared to setting values directly on a component, this approach is common for many Angular Material controls. The advantage lies in setting it once and allowing everything to inherit the configuration.

Tips for refreshing the value of a dependency injection token

Answer №1

Answer №2

Answer №3

Answer №4

Explaining the Reason Why...

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