[Angular] Angular Custom Change Detection with ChangeDetectorRef

Each component has its own ChangeDetectorRef,and we can inject ChangeDetectorRef into constructor:

export class ChildComponent implements OnInit {

  constructor(
    private cdr: ChangeDetectorRef
  )

 

For example if you have a huge list can be updated in real time though some real time database.

Update in real time is really expensive for huge list. 

 

We have build a custom change detector,for example,update every 5 seconds,to check changes,to do that,we need to two things,

1. disable default change detector

2. Check for changes every 5 seconds.

import { Component,OnInit,ChangeDetectorRef } from ‘@angular/core‘;
import { ListService } from ‘./list.service‘;

@Component({
  selector: ‘app-child‘,templateUrl: ‘./child.component.html‘,styleUrls: [‘./child.component.css‘]
})
export class ChildComponent implements OnInit {

  constructor(
    private cdr: ChangeDetectorRef,private dataProvider: ListService
  ) { 
    // disable default change detector
    cdr.detach();
    // Now every 5second,do a check for its child tree
    setInterval(() => { this.cdr.detectChanges(); },5000);
  }

  ngOnInit() {
  }

}

 

There is another API: reattach() which uses for reset to default Angular change dectctor.