Building a Structural Directive in Angular

unless.directive.ts

import {Directive, Input, TemplateRef, ViewContainerRef} from '@angular/core';

@Directive({
  selector: '[appUnless]'
})
export class UnlessDirective {

  @Input() set appUnless(condition: boolean) {
    if (!condition) {
      this.vcRef.createEmbeddedView(this.templateRef);
    } else {
      this.vcRef.clear();
    }
  }

  constructor(private templateRef: TemplateRef<any>, private vcRef: ViewContainerRef) {
  }

}

app.component.html

<P *appUnless="true">True</P>
<P *appUnless="false">False</P>

References
https://github.com/mhdr/AngularSamples/tree/master/017/my-app

Binding to Directive Properties in Angular

binding2.directive.ts

import {Directive, HostBinding, HostListener, Input, OnInit} from '@angular/core';

@Directive({
  selector: '[appBinding2]'
})
export class Binding2Directive implements OnInit {

  @Input() defaultColor = 'transparent';
  @Input() highlightColor = 'yellow';

  @HostBinding('style.backgroundColor') backgroundColor = 'transparent';

  constructor() {
  }

  @HostListener('mouseenter') mouseover(eventData: Event) {
    this.backgroundColor = this.highlightColor;
  }

  @HostListener('mouseleave') mouseleave(eventData: Event) {
    this.backgroundColor = this.defaultColor;
  }

  ngOnInit(): void {
    this.backgroundColor = this.defaultColor;
  }
}

app.component.html

<p appBinding2 [defaultColor]="'purple'" [highlightColor]="'orange'">Hello World 5</p>

References
https://github.com/mhdr/AngularSamples/tree/master/015/my-app

Using HostBinding to Bind to Host Properties when Creating Directive in Angular

host-binding.directive.ts

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

@Directive({
  selector: '[appHostBinding]'
})
export class HostBindingDirective {

  @HostBinding('style.backgroundColor') backgroundColor = 'transparent';

  constructor() {
  }

  @HostListener('mouseenter') mouseover(eventData: Event) {
    this.backgroundColor = 'green';
  }

  @HostListener('mouseleave') mouseleave(eventData: Event) {
    this.backgroundColor = 'transparent';
  }
}

app.component.html

<p appHostBinding>Hello World 4</p>

References
https://github.com/mhdr/AngularSamples/tree/master/015/my-app

Using HostListener to Listen to Host Events when Creating Directive in Angular

host-listener.directive.ts

import {Directive, ElementRef, HostListener, OnInit, Renderer2} from '@angular/core';

@Directive({
  selector: '[appHostListener]'
})
export class HostListenerDirective implements OnInit {

  constructor(private elementRef: ElementRef, private renderer: Renderer2) {
  }

  ngOnInit(): void {
  }

  @HostListener('mouseenter') mouseover(eventData: Event) {
    this.renderer.setStyle(this.elementRef.nativeElement, 'background-color', 'green');
  }

  @HostListener('mouseleave') mouseleave(eventData: Event) {
    this.renderer.setStyle(this.elementRef.nativeElement, 'background-color', 'transparent');
  }

}

app.component.html

<p appHostListener>Hello World 3</p>

References
https://github.com/mhdr/AngularSamples/tree/master/015/my-app

Creating an Attribute Directive in Angular

basic-highlight.directive.ts

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

@Directive({
  selector: '[appBasicHighlight]'
})
export class BasicHighlightDirective implements OnInit {

  constructor(private elementRef: ElementRef) {
  }

  ngOnInit(): void {
    this.elementRef.nativeElement.style.backgroundColor = 'red';
  }

}

better-highlight.directive.ts

Using the Renderer to build a Better Attribute Directive

import {Directive, ElementRef, OnInit, Renderer2} from '@angular/core';

@Directive({
  selector: '[appBetterHighlight]'
})
export class BetterHighlightDirective implements OnInit {

  constructor(private elementRef: ElementRef, private renderer: Renderer2) {
  }

  ngOnInit(): void {
    // use this in environments that DOM is not directly accessible like cordova apps
    this.renderer.setStyle(this.elementRef.nativeElement, 'background-color', 'blue');
  }

}

app.component.html

<p appBasicHighlight>Hello World</p>
<p appBetterHighlight>Hello World 2</p>

References
https://github.com/mhdr/AngularSamples/tree/master/016/my-app

Understanding the Component Lifecycle in Angular

ngOnChanges() Respond when Angular (re)sets data-bound input properties. The method receives a SimpleChanges object of current and previous property values.

Called before ngOnInit() and whenever one or more data-bound input properties change.
ngOnInit() Initialize the directive/component after Angular first displays the data-bound properties and sets the directive/component’s input properties.

Called once, after the first ngOnChanges().
ngDoCheck() Detect and act upon changes that Angular can’t or won’t detect on its own.

Called during every change detection run, immediately after ngOnChanges() and ngOnInit().
ngAfterContentInit() Respond after Angular projects external content into the component’s view / the view that a directive is in.

Called once after the first ngDoCheck().
ngAfterContentChecked() Respond after Angular checks the content projected into the directive/component.

Called after the ngAfterContentInit() and every subsequent ngDoCheck().
ngAfterViewInit() Respond after Angular initializes the component’s views and child views / the view that a directive is in.

Called once after the first ngAfterContentChecked().
ngAfterViewChecked() Respond after Angular checks the component’s views and child views / the view that a directive is in.

Called after the ngAfterViewInit() and every subsequent ngAfterContentChecked().
ngOnDestroy() Cleanup just before Angular destroys the directive/component. Unsubscribe Observables and detach event handlers to avoid memory leaks.

Called just before Angular destroys the directive/component.

References
https://angular.io/guide/lifecycle-hooks

Projecting Content into Components with ng-content in Angular

Content projection is a pattern in which you insert, or project, the content you want to use inside another component. For example, you could have a Card component that accepts content provided by another component.

Single-slot content projection

server.component.html

<h2>Title</h2>
<p>
  <ng-content></ng-content>
</p>

app.component.html

<app-server>
  <p><i>Hello World</i></p>
</app-server>

Multi-slot content projection

import { Component } from '@angular/core';

@Component({
  selector: 'app-zippy-multislot',
  template: `
    <h2>Multi-slot content projection</h2>

    Default:
    <ng-content></ng-content>

    Question:
    <ng-content select="[question]"></ng-content>
  `
})
export class ZippyMultislotComponent {}
<app-zippy-multislot>
  <p question>
    Is content projection cool?
  </p>
  <p>Let's learn about content projection!</p>
</app-zippy-multislot>

References
https://github.com/mhdr/AngularSamples/tree/master/015/my-app
https://blog.angular-university.io/angular-ng-content/
https://angular.io/guide/content-projection

Getting Access to the Template DOM with @ViewChild in Angular

<div class="col-md-9">
  <input type="text" class="form-control" trim #nickName />
</div>
<div class="row">
  <button class="btn" (click)="onAddGift(nickName)">Add Gift</button>
</div>
import { Component, OnInit, ViewChild, ElementRef } from '@angular/core';
import { Gift } from '../gift/gift.component';
 
@Component({
  selector: 'app-user',
  templateUrl: './user.component.html',
  styleUrls: ['./user.component.css']
})
export class UserComponent implements OnInit {
  @ViewChild('nickName') nickName : ElementRef;
  userNickName: String = '';
 
  ..
 
  onAddGift(nickName: HTMLInputElement) {
    ..
    this.userNickName = nickName.nativeElement.value;
    ..
  }
  
}

References
http://www.jcombat.com/angular-5/local-references-in-angular

Local References in Angular

Note that we can only access local references in template, not on TypeScript code

<div class="col-md-9">
  <input type="text" class="form-control" trim #giftName />
</div>
<div class="row">
  <button class="btn" (click)="onAddGift(giftName)">Add Gift</button>
</div>
import { Component, OnInit, ViewChild, ElementRef } from '@angular/core';
import { Gift } from '../gift/gift.component';
 
@Component({
  selector: 'app-user',
  templateUrl: './user.component.html',
  styleUrls: ['./user.component.css']
})
export class UserComponent implements OnInit {
  userNickName: String = '';
 
  ..
 
  onAddGift(giftName: HTMLInputElement) {
    this.userGiftName = giftName.value;
    ..
    ..
  }
  
}

There is another way to do this using @ViewChild decorator.

References
http://www.jcombat.com/angular-5/local-references-in-angular