Angular 2 Read More Directive

问题:

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.

回答1:

I think you'll need a Component rather then Directive. Components makes more sense since you need to add Read more button/link, i.e. update DOM.

@Component({
    selector: 'read-more',
    template: `
        <div [class.collapsed]="isCollapsed">
            <ng-content></ng-content>
        </div>
        <div (click)="isCollapsed = !isCollapsed">Read more</div>
    `,
    styles: [`
        div.collapsed {
            height: 250px;
            overflow: hidden;
        }
    `]
})

export class ReadMoreComponent {
    isCollapsed = true;
}

Usage:

<read-more>
   <!-- you HTML goes here -->
</read-more>

回答2:

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>

回答3:

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>

回答4:

import { Component, Input,OnChanges} from '@angular/core';
@Component({    
    selector: 'read-more',
    template: `
        <div [innerHTML]="currentText"></div>
        <span *ngIf="showToggleButton">
            <a (click)="toggleView()">Read {{isCollapsed? 'more':'less'}}</a>
        </span>`
})

export class ReadMoreDirective implements OnChanges {

    @Input('text') text: string;
    @Input('maxLength') maxLength: number = 100;
    @Input('showToggleButton')showToggleButton:boolean;

    currentText: string;

    public isCollapsed: boolean = true;

    constructor(
        //private elementRef: ElementRef
    ) {

    }
    toggleView() {
        this.isCollapsed = !this.isCollapsed;
        this.determineView();
    }

    determineView() {

        if (this.text.length <= this.maxLength) {
            this.currentText = this.text;
            this.isCollapsed = false;
            return;
        }

        if (this.isCollapsed == true) {
            this.currentText = this.text.substring(0, this.maxLength) + "...";
        } else if(this.isCollapsed == false)  {
            this.currentText = this.text;
        }

    }

    ngOnChanges() {
        if(!this.validateSource(this.text)) {
            //throw 'Source must be a string.';
            console.error('Source must be a string.');
        }
        else{
            this.determineView();
        }
    }

    validateSource(s) {
        if(typeof s !== 'string') {
            return false;
        } else {
            return true;
        }
    }
}

and usage

<read-more [text]="this is test text" [maxLength]="10" [showToggleButton]="true"></read-more>

回答5:

If you want to display the text to the maximum number of chars without cutting any word, change this line of code:

this.currentText = this.text.substring(0, this.maxLength) + "...";

To:

this.currentText = this.text.substring(0, this.maxLength);
this.currentText = this.currentText.substr(0, Math.min(this.currentText.length, this.currentText.lastIndexOf(" ")))
this.currentText = this.currentText + "..."

回答6:

Just a slight improvement of @Andrei Zhytkevich code (useful for markdown)

import {
  Component,
  AfterViewInit,
  ViewChild,
  ElementRef,
  Attribute,
  ChangeDetectionStrategy } from '@angular/core';

@Component({
  changeDetection: ChangeDetectionStrategy.OnPush,
  selector: 'ui-read-more',
  template: `
    <div [class.collapsed]="isCollapsed" [style.height]="_height">
      <div #wrapper>
        <ng-content></ng-content>
      </div>
    </div>
    <div class="read-more">
      <button
      type="button"
      class="btn btn-light" (click)="onIsCollapsed()">{{isCollapsed ? 'More' : 'Less'}}</button>
    </div>
  `,
  styles: [`
    :host{
      display: block;
    }
    .collapsed {
      overflow: hidden;
      padding-bottom: 1rem;
    }
    .read-more{
      display: flex;
      justify-content: flex-end;
    }
  `]
})
export class UiReadMoreComponent implements AfterViewInit{
  @ViewChild('wrapper') wrapper: ElementRef;
  isCollapsed: boolean = true;
  private contentHeight: string;
  private _height: string;
  constructor(@Attribute('height') public height: string = '') {
    this._height = height;
  }
  ngAfterViewInit() {
    this.contentHeight = this.wrapper.nativeElement.clientHeight + 'px';
  }
  onIsCollapsed(){
    this.isCollapsed = !this.isCollapsed;
    this._height = this.isCollapsed ? this.height : this.contentHeight;
  }
}

Usage

<ui-read-more height="250px">
 <ngx-md>
    {{post.content}}
 </ngx-md>
</ui-read-more>

回答7:

Thank you, I changed it up a bit for it be on NgOnInit because of the console error. There's a slight change to it and works well with Angular 6.

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

    a {
      color: #007bff !important;
      cursor: pointer;
    }
`]
})
export class ReadMoreComponent implements OnInit {

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

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

// set these to false to get the height of the expended container 
public isCollapsed = false;
public isCollapsible = false;

constructor(private elementRef: ElementRef) {
}

ngOnInit() {
  const currentHeight = document.getElementById('textCollapse').offsetHeight;
  if (currentHeight > this.maxHeight) {
    this.isCollapsed = true;
    this.isCollapsible = true;
  }
 }
}

As you can see I changed the
const current Height = document.getElementById('textCollapse').offsetHeight;

回答8:

Again i solved these types of problem with dynamic data and full controlling.

 <div class="Basic-Info-para">
   <p>
     <span *ngIf="personalBasicModel.professionalSummary.length>200" id="dots"> 
         {{personalBasicModel.professionalSummary | slice:0:200}} ...
    </span>
     <span id="more">{{personalBasicModel.professionalSummary }}
</span>
 </p>
</div> 

Here , personalBasicModel.professionalSummary contain string . like any text.
slice:0:200 = use slice pipe for splice string with 200 character length . you can be change length according your requirement. id="dots" & id="more" two important thing.

<div class="Basic-Info-SeeMore">
            <button class="SeeMore"(click)="showMore(paasValueOn_SeeMoreBtn)">
                {{showLess_More}}
            </button>
        </div>

Here we define a button with dynamic text (see more and see less ) with click event.

//---------------------------------- ts file -----------------------------------//

Define variable

showLess_More : string = "SEE MORE...";
paasValueOn_SeeMoreBtn : boolean = true;

Event(Method) fire when user click on see more button

 showMore(data:boolean){
    if(data){
      $("#dots").css('display', 'none');
      $("#more").css('display', 'inline');
      this.showLess_More = "SEE LESS ...";
      this.paasValueOn_SeeMoreBtn = false;
    }else{
      $("#dots").css('display', 'inline');
      $("#more").css('display', 'none');
      this.showLess_More = "SEE MORE...";
      this.paasValueOn_SeeMoreBtn = true;

    }

  }

回答9:

You can use this plugin.

It is very simple to use only to pass [text] and [textLength] which you want to show by default https://www.npmjs.com/package/nga-read-more

回答10:

lineheight approach:-

lineheight and little calculation and some css text-overflow: ellipsis; does this job.

.css

.descLess {
  margin-bottom: 10px;
  text-overflow: ellipsis;
  overflow: hidden;
  word-wrap: break-word;
  display: -webkit-box;
  line-height: 1.8;      <==== adjust line-height...a/q to your need
  letter-spacing: normal;
  white-space: normal;
  max-height: 52px;  <==== 250px etc:-
  width: 100%;
  /* autoprefixer: ignore next */
  -webkit-line-clamp: 2; <==== clamp line 2...or 3 or 4 or 5...
  -webkit-box-orient: vertical;
}

.html

    <div class="col-12 rmpm">
          <div id="descLess" *ngIf="seeMoreDesc === 'false'" class="descLess col-12 rmpm">
                {{inputData?.desc}}
           </div>
        <div *ngIf="seeMoreDesc === 'true'" class="col-12 rmpm" style="margin-bottom: 10px;line-height: 1.8;"> 
   <!--Use Line height here-->
                {{inputData?.desc}}
               </div>
        <span class="seeMore" *ngIf="seeMoreDesc === 'false' && lineHeightDesc > 21"
             (click)="updateSeeMore('seeMoreDesc', 'true')">
                 See More
        </span>
        <span class="seeMore" *ngIf="seeMoreDesc === 'true'"
               (click)="updateSeeMore('seeMoreDesc', 'false')">
                   See Less
        </span>
         </div>

.ts

declare const $:any;
seeMoreDesc = 'false';
seeMore = '';
inputData = {
   'desc':'Lorem Ipusme dummy text..................'
 }
 constructor(
        private eRef: ElementRef,
        private cdRef : ChangeDetectorRef
    ) {}
    ngAfterViewChecked() {
       // pass line height here
        this.lineHeightDesc = (Number($('#descLess').height()) / 1.8);
        this.cdRef.detectChanges();
    }


     public updateSeeMore(type, action) {
         if (type === 'seeMoreDesc') {
               this.seeMoreDesc = action;
                this.cdRef.detectChanges();
            } else if (type === 'seeMore') {
                this.seeMore = action;
                this.cdRef.detectChanges();
            }

        }