Templates & Directives - Textnotes

Templates & Directives

Angular templates define the HTML structure of a component. Directives are special instructions that modify the DOM behavior or appearance in your templates. Directives are of two main types: Structural Directives (change DOM structure) and Attribute Directives (change element appearance or behavior).

1. Structural Directives

Structural directives change the layout or structure of the DOM.

*1.1 ngIf

Used to conditionally show or hide elements.


<p *ngIf="isLoggedIn">Welcome, user!</p>
<p *ngIf="!isLoggedIn">Please login</p>

isLoggedIn = true;

*1.2 ngFor

Used to render lists dynamically.


<ul>
<li *ngFor="let item of items">{{ item }}</li>
</ul>

items = ['Angular', 'React', 'Vue'];

*1.3 ngSwitch

Used to conditionally display one element from multiple options.


<div [ngSwitch]="color">
<p *ngSwitchCase="'red'">Red selected</p>
<p *ngSwitchCase="'blue'">Blue selected</p>
<p *ngSwitchDefault>Other color</p>
</div>

color = 'blue';

2. Attribute Directives

Attribute directives change the appearance or behavior of elements without changing the DOM structure.

2.1 ngClass

Adds or removes CSS classes dynamically.


<p [ngClass]="{'active': isActive, 'inactive': !isActive}">Status</p>

isActive = true;

2.2 ngStyle

Dynamically sets inline CSS styles.


<p [ngStyle]="{'color': textColor, 'font-size.px': fontSize}">Styled Text</p>

textColor = 'red';
fontSize = 18;

2.3 Custom Directives

You can create your own directives to add custom behavior.

Example: HighlightDirective


import { Directive, ElementRef, HostListener } from '@angular/core';

@Directive({
selector: '[appHighlight]'
})
export class HighlightDirective {
constructor(private el: ElementRef) { }

@HostListener('mouseenter') onMouseEnter() {
this.el.nativeElement.style.backgroundColor = 'yellow';
}

@HostListener('mouseleave') onMouseLeave() {
this.el.nativeElement.style.backgroundColor = '';
}
}

Usage in template:


<p appHighlight>Hover to highlight me!</p>

Summary

  1. Templates define the UI structure of a component.
  2. Structural Directives (*ngIf, *ngFor, *ngSwitch) manipulate DOM elements.
  3. Attribute Directives (ngClass, ngStyle) change the appearance of elements.
  4. Custom directives allow you to implement reusable behavior across your application.