Updating component view triggered by service - Provider for ChangeDetectorRef not found

Question

Updating component view triggered by service - Provider for ChangeDetectorRef not found

I need to update my application view based on events from a service.

One of my services is injecting the ChangeDetectorRef. Compilation is successful, but I am encountering an error in the browser during App bootstrap:

No provider for ChangeDetectorRef!

.

I initially thought I should include it in my AppModule, but I couldn't find any documentation suggesting that it is importable there. Adding the class itself to the import array resulted in an error. Likewise, adding it to the providers array in the module caused an error as well. Below is a simplified version of my service:

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

@Injectable()
export class MyService {
  private count: number = 0;
  constructor(private ref: ChangeDetectorRef){}

  increment() {
    this.count++;
    this.ref.detectChanges();
}

And here is the app module:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';

import { AppComponent } from './app.component';

import { MyService } from './my.service';

@NgModule({
  imports: [ BrowserModule ],
  declarations: [ AppComponent ],
  providers: [ MyService ],
  booststrap: [ AppComponent ]
})
export AppModule {}

UPDATE

I attempted to remove my use of ChangeDetectorRef, but the issue persists. It seems like there may be an issue with how I updated my System JS config.

The initial app was created using angular-cli, and I decided to manually update Angular since they hadn't done so yet. However, with the release of Angular 2.0.0, angular-cli has been updated to support the latest version of Angular. I will follow their upgrade procedures and hopefully resolve the problem.

Update 2

The webpack/angular-cli update went smoothly. The app now successfully builds with Angular 2.0.0 and angular-cli 1.0.0-beta14. However, the browser still shows the same error. Removing ChangeDetectorRef from the service didn't truly fix the issue as I realized it was being used in two services. By removing it from both files, the app loads successfully except for areas where ChangeDetectorRef was needed. Reintroducing it into one file triggers an error about the provider not being found.

I tried importing it into my module, but since it's not a module itself, the transpiler raises an error. Listing it as a provider in the module also failed since it lacks a 'provide' property. Similar issues arise if I attempt to include it in the declarations array.

angular typescript angular2-changedetection

Answer 1

Answer №1

ChangeDetectorRef is not the best option in this situation. It is designed to detect changes in a specific component and its children.

Instead, consider using ApplicationRef:

import {Injectable, ApplicationRef } from '@angular/core';

@Injectable()
export class MyService {
  private count: number = 0;
  constructor(private ref: ApplicationRef) {}

  increment() {
    this.count++;
    this.ref.tick();
  }
}

I have tested this solution with Observables and it works seamlessly:

import { ApplicationRef, Injectable } from '@angular/core';
import { Observable, ReplaySubject } from "rxjs/Rx";
import * as childProcess from 'child_process';

@Injectable()
export class Reader {

    private output: ReplaySubject<string> = new ReplaySubject<string>(0);

    constructor(private ref: ApplicationRef) {
        var readerProcess = childProcess.spawn('some-process');
        readerProcess.stdout.on('data', (data) => {
            this.output.next(data.toString());
            this.ref.tick();
        });
    }

    public getOutput():Observable<string> {
        return this.output;
    }
}

Below is an example of a component that utilizes this functionality:

import {Component} from '@angular/core';
import { ReplaySubject, Observable } from "rxjs/Rx";

import { Reader } from './reader/reader.service';

@Component({
    selector: 'app',
    template: `
    output:
    <div>{{output}}</div>
    `
})
export class App {

    public output: string;

    constructor(private reader: Reader) {}

    ngOnInit () {
        this.reader.getOutput().subscribe((val : string) => {
            this.output = val;
        });
    }
}

Answer 2

ChangeDetectorRef is not the best option in this situation. It is designed to detect changes in a specific component and its children.

Instead, consider using ApplicationRef:

import {Injectable, ApplicationRef } from '@angular/core';

@Injectable()
export class MyService {
  private count: number = 0;
  constructor(private ref: ApplicationRef) {}

  increment() {
    this.count++;
    this.ref.tick();
  }
}

I have tested this solution with Observables and it works seamlessly:

import { ApplicationRef, Injectable } from '@angular/core';
import { Observable, ReplaySubject } from "rxjs/Rx";
import * as childProcess from 'child_process';

@Injectable()
export class Reader {

    private output: ReplaySubject<string> = new ReplaySubject<string>(0);

    constructor(private ref: ApplicationRef) {
        var readerProcess = childProcess.spawn('some-process');
        readerProcess.stdout.on('data', (data) => {
            this.output.next(data.toString());
            this.ref.tick();
        });
    }

    public getOutput():Observable<string> {
        return this.output;
    }
}

Below is an example of a component that utilizes this functionality:

import {Component} from '@angular/core';
import { ReplaySubject, Observable } from "rxjs/Rx";

import { Reader } from './reader/reader.service';

@Component({
    selector: 'app',
    template: `
    output:
    <div>{{output}}</div>
    `
})
export class App {

    public output: string;

    constructor(private reader: Reader) {}

    ngOnInit () {
        this.reader.getOutput().subscribe((val : string) => {
            this.output = val;
        });
    }
}

Answer 3

Answer №2

If you're looking for a way to initiate changes from a service while letting components determine how and when they respond, setting up subscriptions could be the solution.

To do this, add an EventEmitter in your service:

changeDetectionEmitter: EventEmitter<void> = new EventEmitter<void>();

Whenever an event occurs in the service that may require triggering a change detection cycle, simply emit it:

this.changeDetectionEmitter.emit();

In components utilizing this service, they can subscribe to listen for potential triggers and react accordingly:

this.myService.changeDetectionEmitter.subscribe(
    () => {
      this.cdRef.detectChanges();
    },
    (err) => {
      // handle errors...
    }
  );

This approach allows components to maintain control over change detection while keeping logic centralized in the service. The service doesn't need to understand anything about the UI; it simply notifies listeners of any updates.

Answer 4

If you're looking for a way to initiate changes from a service while letting components determine how and when they respond, setting up subscriptions could be the solution.

To do this, add an EventEmitter in your service:

changeDetectionEmitter: EventEmitter<void> = new EventEmitter<void>();

Whenever an event occurs in the service that may require triggering a change detection cycle, simply emit it:

this.changeDetectionEmitter.emit();

In components utilizing this service, they can subscribe to listen for potential triggers and react accordingly:

this.myService.changeDetectionEmitter.subscribe(
    () => {
      this.cdRef.detectChanges();
    },
    (err) => {
      // handle errors...
    }
  );

This approach allows components to maintain control over change detection while keeping logic centralized in the service. The service doesn't need to understand anything about the UI; it simply notifies listeners of any updates.

Answer 5

Answer №3

It's been a while since I should have done this, but I attempted to simply pass the ChangeDetectorRef to the Service through the function being called.

//myservice
import { Injectable, ChangeDetectorRef } from '@angular/core';

@Injectable()
export class MyService {
  constructor(){}

  increment(ref: ChangeDetectorRef, output: number) {
    output++;
    ref.detectChanges();
}

The Component

import {Component} from '@angular/core';
import { MyService } from './myservice.service';

@Component({
    selector: 'app',
    template: `
    output:
    <div>{{output}}</div>
    `
})
export class App {

    public output: number;

    constructor(public ref: ChangeDetectorRef, private myService: MyService) {}

    ngOnInit () {
       this.myService.increment(this.ref,output)
    }
}

Answer 6

It's been a while since I should have done this, but I attempted to simply pass the ChangeDetectorRef to the Service through the function being called.

//myservice
import { Injectable, ChangeDetectorRef } from '@angular/core';

@Injectable()
export class MyService {
  constructor(){}

  increment(ref: ChangeDetectorRef, output: number) {
    output++;
    ref.detectChanges();
}

The Component

import {Component} from '@angular/core';
import { MyService } from './myservice.service';

@Component({
    selector: 'app',
    template: `
    output:
    <div>{{output}}</div>
    `
})
export class App {

    public output: number;

    constructor(public ref: ChangeDetectorRef, private myService: MyService) {}

    ngOnInit () {
       this.myService.increment(this.ref,output)
    }
}

Answer 7

Answer №4

The most recent versions have integrated it into the core functionality, so all you need to do is refer to the core using the necessary variable and you should be good to go

import { TestBed } from '@angular/core/testing';
import { ChangeDetectorRef } from '@angular/core';
import { MyService } from './my.service';

describe('MyService', () => {
    beforeEach(() => TestBed.configureTestingModule({
        providers: [ChangeDetectorRef] // <--- SEE HERE I'M A PROVIDER!
    }));

    it('should be created', () => {
        const service: MyService = TestBed.get(MyService);
        expect(service).toBeTruthy();
    });
});

I trust this information is helpful

Answer 8

The most recent versions have integrated it into the core functionality, so all you need to do is refer to the core using the necessary variable and you should be good to go

import { TestBed } from '@angular/core/testing';
import { ChangeDetectorRef } from '@angular/core';
import { MyService } from './my.service';

describe('MyService', () => {
    beforeEach(() => TestBed.configureTestingModule({
        providers: [ChangeDetectorRef] // <--- SEE HERE I'M A PROVIDER!
    }));

    it('should be created', () => {
        const service: MyService = TestBed.get(MyService);
        expect(service).toBeTruthy();
    });
});

I trust this information is helpful

Answer 9

Answer №5

Utilizing the ApplicationRef can be a helpful approach. Here are a couple more methods to consider:

Implementation of setTimeout

@Injectable()
export class MyService {
  private count: number = 0;
  constructor(){}

  increment() {
    setTimeout(() => this.count++, 0);
  }
}

Employing Promise

@Injectable()
export class MyService {
  private count: number = 0;
  constructor(){}

  increment() {
    Promise.resolve().then(() => this.count++);
  }
}

Both of these methods prompt Angular to initiate change detection. If you utilize Zone.js for change detection - this method is standard and used by 99% of applications.

Answer 10

Utilizing the ApplicationRef can be a helpful approach. Here are a couple more methods to consider:

Implementation of setTimeout

@Injectable()
export class MyService {
  private count: number = 0;
  constructor(){}

  increment() {
    setTimeout(() => this.count++, 0);
  }
}

Employing Promise

@Injectable()
export class MyService {
  private count: number = 0;
  constructor(){}

  increment() {
    Promise.resolve().then(() => this.count++);
  }
}

Both of these methods prompt Angular to initiate change detection. If you utilize Zone.js for change detection - this method is standard and used by 99% of applications.

Answer 11

Answer №6

In order to integrate your service at the component level, you must include it in the providers section:

@Component({
  // ...
  providers: [MyService]
})
export class AnotherComponent {
  // ...
}

Answer 12

In order to integrate your service at the component level, you must include it in the providers section:

@Component({
  // ...
  providers: [MyService]
})
export class AnotherComponent {
  // ...
}

Updating component view triggered by service - Provider for ChangeDetectorRef not found

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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