Angular - Call child component method from parent component

Angular enables the components based development which helps you create small cohesive components to design the application in a manageable approach. This may also lead to a complex heirarchy among the components. Then you need a mechanism to communicate between these components which may be in two directions top-down and bottom-up.

In this post we will see an example of top-down approach to allow communication from the parent component to the child component.

Lets say we have two components, ParentComponent and ChildComponent, with structure like this.

<parent-component>
    <child-component />
</parent-component>

The parent-component has a button called Search, which needs to invoke the child-component's method loadData();

Lets walk through this example to see how we can achieve this behavior.

This is the child component's ts file:

// child.component.ts
import { Component } from '@angular/core';

@Component({
    selector: 'child-component',
    template: '<p>{{ message }}</p>'
})

class ChildComponent {
    message: String = 'Hello World!';

    loadData() {
        console.log('loading data from service');
    }
}

This is the parent component's ts file:

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

@Component({
    selector: 'parent-component',
    template: `
        <child-component />
	<button (click)="parentLocalMethod()">Call Child Component Method</button>    
	`
})

export class ParentComponent {

    parentLocalMethod() {
	//here we need to call the child component's method
    }
}

To enable the parent component to invoke child-component's method, we have to makes these changes in parent-component's ts file:

First import ViewChild from '@angular/core'

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

Import the ChildComponent class iteself:

import { ChildComponent } from '../components/child.component';

To enable the access for child-component, we can inject the child component into the parent with the help of ViewChild decorator.

@ViewChild('childComponentTemplateVariable') tempChildComponent: ChildComponent;

Where childComponentTemplateVariable passed to the ViewChild decorator is the template variable (with # symbol) we need to set in the parent template's html for child-component tag:

<child-component #childComponentTemplateVariable />

Finally we can call the child-component's method by using the variable we have defined with ViewChild decorator. Like:

tempChildComponent.loadData();

The complete listing of the parent-component's ts file will be look like this:

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

@Component({
    selector: 'parent-component',
    template: `
        <child-component #childComponentTemplateVariable />
	<button (click)="parentLocalMethod()">Call Child Component Method</button>    
	`
})

export class ParentComponent {

    @ViewChild('childComponentTemplateVariable') tempChildComponent: ChildComponent;

    parentLocalMethod() {
	//calling child-component's method
	tempChildComponent.loadData();
    }
}

ngAfterViewInit

When working with child components using the ViewChild decorator, an important thing to consider is the ngAfterViewInit lifecycle hook.

Respond after Angular initializes the component's views and child views, or the view that contains the directive.

The child component isn't available until after Angular displays the parent view. So if you are planning to process something once the view is loaded, then the best approach could be to use the ngAfterViewInit lifecycle hook to process any initialization code.

In the example above, we have called the child-components method from a button click event on the parent-component.

In case if we need to call the child-components method right after the view is loaded, then we can use the lifecycle hook ngAfterViewInit. To use the ngAfterViewInit we have to import the reference for the interace AfterViewInit and then define the ngAfterViewInit hook body.


import { Component, OnInit, ViewChild, AfterViewInit  } from '@angular/core';

//...

ngAfterViewInit() {
tempChildComponent.loadData();
}

References:

Angular - Lifecycle hooks

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January 24, 2022