Injection of dependencies in Angular can be done outside of the constructor

Question

Injection of dependencies in Angular can be done outside of the constructor

In my class, I have a constructor that takes in some data.

export class MyClass {

   constructor(data: any) {
     this.data = data;
  }
}

I also want to include ChangeDetectorRef as a parameter in the constructor like this.

constructor(data: any, cd: ChangeDetectorRef )

However, if I do this, I am unable to create an object from MyClass using

const myClass = new MyClass(data)

Is there a way to inject ChangeDetectorRef outside of the constructor?

angular typescript dependency-injection angular5

Answer 1

Answer №1

Another approach could be to implement a setter method that must be called once you have the correct reference.

export class MyClass 
{
    private cd: ChangeDetectorRef;
    constructor(data: any ) {
    this.data = data;
    }

    setChangeDetector(cd: ChangeDetectorRef )
    {
       this.cd = cd;
    }
}

Exploring alternative solutions

While not exactly using dependency injection, another option is to assign a global reference to the ChangeDetectorRef during the initialization of your main module

module.ts

 import {ChangeDetectorRef} from '@angular/core';

  export let CDInstance: ChangeDetectorRef;

  export class AppModule
  {
    constructor(private cd: ChangeDetectorRef)
    {
      CDInstance = this.cd;
    }
  }

myclass.ts

import {InjectorInstance} from './app.module';

export class MyClass
{

  private cd: ChangeDetectorRef;

  constructor(data: any)
  {
    this.data = data;
    this.cd = CDInstance;
  }
}

Answer 2

Another approach could be to implement a setter method that must be called once you have the correct reference.

export class MyClass 
{
    private cd: ChangeDetectorRef;
    constructor(data: any ) {
    this.data = data;
    }

    setChangeDetector(cd: ChangeDetectorRef )
    {
       this.cd = cd;
    }
}

Exploring alternative solutions

While not exactly using dependency injection, another option is to assign a global reference to the ChangeDetectorRef during the initialization of your main module

module.ts

 import {ChangeDetectorRef} from '@angular/core';

  export let CDInstance: ChangeDetectorRef;

  export class AppModule
  {
    constructor(private cd: ChangeDetectorRef)
    {
      CDInstance = this.cd;
    }
  }

myclass.ts

import {InjectorInstance} from './app.module';

export class MyClass
{

  private cd: ChangeDetectorRef;

  constructor(data: any)
  {
    this.data = data;
    this.cd = CDInstance;
  }
}

Answer 3

Answer №2

If you need to set a value using a setter method in TypeScript:

export class ExampleClass {
   ref: RefType;
   constructor(data: any) {
     this.data = data;
   }

   setRef(value: RefType) { this.ref = value; }
}

Answer 4

If you need to set a value using a setter method in TypeScript:

export class ExampleClass {
   ref: RefType;
   constructor(data: any) {
     this.data = data;
   }

   setRef(value: RefType) { this.ref = value; }
}

Answer 5

Answer №3

To make ChangeDetectorRef optional in the constructor, simply add it as an optional parameter:

export class MyClass {
   constructor(data: any, cd?: ChangeDetectorRef ) {
     this.data = data;
  }
}

Then you can create an instance of MyClass without providing ChangeDetectorRef like this:

const myClass = new MyClass(data)

Update:

If you need to use ChangeDetectorRef in a service, pass it as an argument from the component:

export class MyComponent{
    constructor(cd : ChangeDetectorRef ){
       const myClass = new MyClass(data, cd);
    }
}

Answer 6

To make ChangeDetectorRef optional in the constructor, simply add it as an optional parameter:

export class MyClass {
   constructor(data: any, cd?: ChangeDetectorRef ) {
     this.data = data;
  }
}

Then you can create an instance of MyClass without providing ChangeDetectorRef like this:

const myClass = new MyClass(data)

Update:

If you need to use ChangeDetectorRef in a service, pass it as an argument from the component:

export class MyComponent{
    constructor(cd : ChangeDetectorRef ){
       const myClass = new MyClass(data, cd);
    }
}

Injection of dependencies in Angular can be done outside of the constructor

Answer №1

Answer №2

Answer №3

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