Change Detection Strategy in Angular

Change detection in Angular is the mechanism that ensures the UI is updated in response to changes in the application state. This tutorial covers the basics of change detection strategy and how to use it effectively in your Angular applications.

What is Change Detection?

Change detection is the process by which Angular checks the component's data and updates the DOM when necessary. It ensures that the view is always in sync with the component's state.

Change Detection Strategies

Angular provides two change detection strategies:

• Default: Angular checks every component in the component tree for changes during each change detection cycle.
• OnPush: Angular only checks the component and its subtree when an input property changes or an event originates from the component or its children.

Using Default Change Detection Strategy

The default change detection strategy is used when no specific strategy is set. Angular checks the entire component tree for changes during each change detection cycle:

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

@Component({
  selector: 'app-default-strategy',
  template: '<div>Default Strategy Component</div>',
})
export class DefaultStrategyComponent {}

Using OnPush Change Detection Strategy

The OnPush change detection strategy can be used to optimize performance by limiting when Angular checks for changes:

import { Component, ChangeDetectionStrategy } from '@angular/core';

@Component({
  selector: 'app-on-push-strategy',
  template: '<div>OnPush Strategy Component</div>',
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class OnPushStrategyComponent {}

Detecting Changes Manually

With the OnPush strategy, you might need to trigger change detection manually using the ChangeDetectorRef service:

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

@Component({
  selector: 'app-manual-detection',
  template: '<div>Manual Detection Component</div>',
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class ManualDetectionComponent {
  constructor(private cdr: ChangeDetectorRef) {}

  triggerChangeDetection() {
    this.cdr.detectChanges();
  }
}

Key Points

Conclusion

Understanding and using change detection strategies effectively in Angular can significantly improve the performance of your applications. By choosing the right strategy and triggering change detection manually when necessary, you can ensure that your Angular applications are both efficient and responsive. Happy coding!