Angular 7 | Directives
Directives in Angular 7 are Typescript class which is declared with decorator @Directive. These are the Document Object Model (DOM) instruction sets, which decide how logic implementation can be done.
Angular directives can be classified into three types:
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- Component Directives: It forms the main class and is declared by @Component. It contains the details on component processing, instantiated and usage at run time.
Example: It contains certain parameters some of them are shown in this example.
javascript
@Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css']}) |
- There are three parameters discussed below:
- Selector: Tells the template tag which specifies the beginning and end of the component.
- templateURL: Consists of the template used for the component.
- styleUrls: It is of array type which consists of all the style format files used for the template.
- Structural Directives: Structure directives manipulate the DOM elements. These directives have a * sign before the directive. For example, *ngIf and *ngFor.
Example: Let’s look the implementation of *ng-if-else and *ng-for. Using them, we classify weekdays and weekends.
Component file:
javascript
import { Component } from '@angular/core';@Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css']})export class AppComponent { Weekdays:Array =['Sunday', 'Monday', 'Tuesday','Wednesday', 'Thursday', 'Friday', 'Saturday']} |
- Template file:
html
<div *ngFor="let day of Weekdays"><ng-container *ngIf = "(day == 'Saturday' || day == 'Sunday'); else elseTemplate"> <h1>{{day}} is a weekend</h1></ng-container><ng-template #elseTemplate> <h1>{{day}} is not a weekend</h1></ng-template></div> |
- Output:
- Attribute Directives: Attribute directives are used to change the look and behavior of the DOM element. It provides the facility to create our own directive.
Example: This example describes how to make our own directive.
Write command as follows:
ng g directive
- Directive:
javascript
import { Directive, ElementRef, OnInit } from '@angular/core';@Directive({ selector: '[appChanges]'})export class ChangesDirective { constructor(private eltRef: ElementRef) { // Changing the background to green this.eltRef.nativeElement.style.backgroundColor = 'green'; this.eltRef.nativeElement.style.color = 'white'; changing the text color to white } ngOnInit() { }} |
- The Component File:
javascript
import { Component, OnInit, Directive } from '@angular/core';import { ChangesDirective } from '../changes.directive';@Component({ selector: 'app-derived-directive', templateUrl: './derived-directive.component.html', styleUrls: ['./derived-directive.component.css']})export class DerivedDirectiveComponent implements OnInit { isClicked:boolean=false; constructor() { } buttonClick(){ // Change controlled by button press this.isClicked = true; } ngOnInit() { }} |
- The Template
html
<button>Click Here</button> <div style="width: 220px;height: 50px"> <h1>GeeksForGeeks</h1> </div> <div style="color: green;width: 300px;height: 50px"> <h1> GeeksForGeeks</h1> </div> |
- Output:
- Before clicking the Button:
- Before clicking the Button:
- After clicking the Button:
