Angular 2 Read More Directive

Question

I need to build a readmore directive in Angular2. What this directive will do is for collapse and expand long blocks of text with "Read more" and "Close" links. Not on the basis of the character count but on the basis of the specified max height.

<div read-more [maxHeight]="250px" [innerHTML]="item.details">
</div>

Can anyone please guide what would be the most reliable way to get/set the height of the element for this specific case.

Any guidelines on how this specific directive could be implemented would also be highly appreciated.

I need to build something like this https://github.com/jedfoster/Readmore.js

Solution:

With the help from Andzhik I am able to build the below component that meets my requirements.

import { Component, Input, ElementRef, AfterViewInit } from '@angular/core';

@Component({
    selector: 'read-more',
    template: `
        <div [innerHTML]="text" [class.collapsed]="isCollapsed" [style.height]="isCollapsed ? maxHeight+'px' : 'auto'">
        </div>
            <a *ngIf="isCollapsable" (click)="isCollapsed =! isCollapsed">Read {{isCollapsed? 'more':'less'}}</a>
    `,
    styles: [`
        div.collapsed {
            overflow: hidden;
        }
    `]
})
export class ReadMoreComponent implements AfterViewInit {

    //the text that need to be put in the container
    @Input() text: string;

    //maximum height of the container
    @Input() maxHeight: number = 100;

    //set these to false to get the height of the expended container 
    public isCollapsed: boolean = false;
    public isCollapsable: boolean = false;

    constructor(private elementRef: ElementRef) {
    }

    ngAfterViewInit() {
        let currentHeight = this.elementRef.nativeElement.getElementsByTagName('div')[0].offsetHeight;
       //collapsable only if the contents make container exceed the max height
        if (currentHeight > this.maxHeight) {
            this.isCollapsed = true;
            this.isCollapsable = true;
        }
    }
}

Usage:

<read-more [text]="details" [maxHeight]="250"></read-more>

If there could be any improvements, please feel free to suggest.

Answer 1

I made a version that uses character length rather than div size.

import { Component, Input, ElementRef, OnChanges} from '@angular/core';

@Component({    
    selector: 'read-more',
    template: `
        <div [innerHTML]="currentText">
        </div>
            <a [class.hidden]="hideToggle" (click)="toggleView()">Read {{isCollapsed? 'more':'less'}}</a>
    `
})

export class ReadMoreComponent implements OnChanges {
    @Input() text: string;
    @Input() maxLength: number = 100;
    currentText: string;
    hideToggle: boolean = true;

    public isCollapsed: boolean = true;

    constructor(private elementRef: ElementRef) {

    }
    toggleView() {
        this.isCollapsed = !this.isCollapsed;
        this.determineView();
    }
    determineView() {
        if (!this.text || this.text.length <= this.maxLength) {
            this.currentText = this.text;
            this.isCollapsed = false;
            this.hideToggle = true;
            return;
        }
        this.hideToggle = false;
        if (this.isCollapsed == true) {
            this.currentText = this.text.substring(0, this.maxLength) + "...";
        } else if(this.isCollapsed == false)  {
            this.currentText = this.text;
        }

    }
    ngOnChanges() {
        this.determineView();       
    }
}

Usage:

<read-more [text]="text" [maxLength]="100"></read-more>