No, an event triggered in a child component cannot directly cause change detection in the parent component with the `OnPush` change detection strategy in Angular. The `OnPush` strategy only triggers change detection in a component when one of its input properties changes or when an event emitted by the component itself or its child components is received. However, you can propagate changes from the child component to the parent component using techniques like EventEmitter or a shared service. Here's an example to illustrate how you can achieve this: 

// child.component.ts
import { Component, Output, EventEmitter, ChangeDetectionStrategy } from '@angular/core';

@Component({
  selector: 'app-child',
  template: `
    <button (click)="triggerEvent()">Trigger Event</button>
  `,
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class ChildComponent {
  @Output() childEvent: EventEmitter = new EventEmitter();

  triggerEvent() {
    this.childEvent.emit(); // Emit event from child component
  }
}



// parent.component.ts
import { Component, ChangeDetectionStrategy } from '@angular/core';

@Component({
  selector: 'app-parent',
  template: `
    <app-child (childevent)="handleChildEvent()"></app-child>
    <p>Event Received: {{ eventReceived }}</p>
  `,
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class ParentComponent {
  eventReceived: boolean = false;

  handleChildEvent() {
    this.eventReceived = true; // Update state in parent component
  }
}
In this example, the `ChildComponent` emits a custom event using the `childEvent` EventEmitter when the button is clicked. The `ParentComponent` listens to this event and triggers the `handleChildEvent()` method, which updates the `eventReceived` property in the parent component. Conclusion: By updating the state in the parent component, Angular's change detection mechanism detects the change and triggers change detection in the parent component, which will update the view accordingly. Please note that while the change detection in the parent component is triggered in response to the event emitted by the child component, it is not directly caused by the event itself. Instead, it is the change in the parent component's state that triggers the change detection.