Introduction
Angular is a comprehensive framework for building enterprise applications. It provides a complete toolkit for designing, building, testing, and deploying applications. One of the key features of Angular is its component-based architecture. Angular provides a set of Lifecycle Hooks that allow developers to tap into the lifecycle of a component and perform actions at specific points in the lifecycle. In this article, we’ll discuss these Lifecycle Hooks in detail.
What Are Component Life Cycle Hooks?
A component can go through a number of stages during its lifetime. These stages include creation, rendering, updating, and destruction. Angular provides a set of Lifecycle Hooks that allow developers to tap into these stages and perform actions when specific events occur. These hooks are functions that are called by the Angular framework at specific points in the component’s lifecycle.
Types of Lifecycle Hooks
In Angular, there are eight Lifecycle Hooks available for components. These hooks can be divided into two categories:
1. ngOnChanges: This hook is called every time a property changes on the component. It receives an object that contains the previous and new values of the property.
2. ngOnInit: This hook is called after the first time that a component is displayed. It is only called once during the lifetime of a component.
3. ngDoCheck: This hook is called every time that the Angular change detection mechanism runs. It is called multiple times during the lifetime of a component.
4. ngAfterContentInit: This hook is called after the content of a component has been projected into its view.
5. ngAfterContentChecked: This hook is called every time that the projected content of a component is checked for changes.
6. ngAfterViewInit: This hook is called after a component’s view has been initialized.
7. ngAfterViewChecked: This hook is called every time that a view of a component is checked for changes.
8. ngOnDestroy: This hook is called just before a component is destroyed.
FAQs
Q. What is the purpose of Component Life Cycle Hooks?
A. The purpose of Component Life Cycle Hooks is to provide a way for developers to tap into the lifecycle of a component and perform actions at specific points in the lifecycle.
Q. When should I use Lifecycle Hooks?
A. You should use Lifecycle Hooks when you want to perform certain actions at specific points in the lifecycle of a component.
Q. What is the difference between ngOnInit and ngAfterViewInit?
A. ngOnInit is called once, after the first time that a component is displayed. ngAfterViewInit is called after a component’s view has been initialized.
Q. When is ngOnDestroy called?
A. ngOnDestroy is called just before a component is destroyed.
Code Example
Here is an example of how to use the ngOnInit hook to initialize a property on a component:
“`
import { Component, OnInit } from ‘@angular/core’;
@Component({
selector: ‘app-my-component’,
template: ‘My Component’,
})
export class MyComponent implements OnInit {
myProperty: string;
ngOnInit() {
this.myProperty = ‘Initialized’;
}
}
“`
Conclusion
Lifecycle Hooks are a powerful feature of Angular that allow developers to tap into the lifecycle of a component and perform specific actions at specific points in the lifecycle. By using these hooks, developers can write code that is more flexible and easier to maintain. In this article, we’ve discussed the types of hooks available and provided a code example.