Component Lifecycle

In this tutorial, we will delve into the concept of the 'Component Lifecycle' in Angular. This is a fundamental concept in Angular that is crucial for every developer to understand. The lifecycle of a component refers to the sequence of phases that a component goes through during its entire life in an application. Angular provides lifecycle hooks that give visibility into these key life moments and the ability to act when they occur.

What is a Component Lifecycle?

In Angular, a component has a lifecycle managed by Angular itself. Angular creates it, renders it, creates and renders its children, checks it when its data-bound properties change, and destroys it before removing it from the DOM. The Component Lifecycle is essentially a sequence of phases or stages that a component goes through from its initiation to its destruction.

Lifecycle Hooks

Angular provides lifecycle hooks that allow us to tap into these critical times in a component's life and enable us to handle them. Here are the lifecycle hooks provided by Angular:

1. ngOnChanges - Respond when Angular sets or resets data-bound input properties.
2. ngOnInit - Initialize the component after Angular first displays the data-bound properties.
3. ngDoCheck - Detect and act upon changes that Angular can't or won't detect on its own.
4. ngAfterContentInit - Respond after Angular projects external content into the component's view.
5. ngAfterContentChecked - Respond after Angular checks the content projected into the component.
6. ngAfterViewInit - Respond after Angular initializes the component's views and child views.
7. ngAfterViewChecked - Respond after Angular checks the component's views and child views.
8. ngOnDestroy - Cleanup just before Angular destroys the directive or component.

Understanding Lifecycle Hooks

ngOnChanges

This hook is called when Angular sets or resets data-bound input properties. The hook receives a SimpleChanges object of current and previous property values. It is called before ngOnInit and whenever one or more data-bound input properties change.

ngOnInit

This is called once, after the first ngOnChanges. Angular calls this hook during the first ngDoCheck. Use it to insert initialization logic.

ngDoCheck

This hook is for the detection and action on changes that Angular cannot or will not detect on its own. For instance, this hook can be used to implement a custom change-detection algorithm for any changes in the component.

ngAfterContentInit

Angular calls this method after it projects the external content into the component's view. This is where you would put the initialization logic for such content.

ngAfterContentChecked

This hook is called after Angular checks the projected content into the component.

ngAfterViewInit

Angular calls this method after initializing the component's views and child views. This is where you would put the initialization logic for such views.

ngAfterViewChecked

This hook is called after Angular checks the component's view and child views.

ngOnDestroy

Angular calls this hook just before it destroys the directive or component. This is where you would put any cleanup logic.

Conclusion

Understanding the Component Lifecycle in Angular is vital as it helps developers to control the rendering process and make the application more efficient and responsive. By using lifecycle hooks, we can perform certain actions when a lifecycle event is triggered. This also helps in managing resources effectively, enhancing the overall performance of the application. With this knowledge, you are now equipped to create even more efficient Angular applications!