Angular 2 阅读更多指令

Question

我需要在 Angular2 中构建一个 readmore 指令。该指令将使用“阅读更多”和“关闭”链接折叠和展开长文本块。不是基于字符数，而是基于指定的最大高度。

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

任何人都可以指导在这种特定情况下获取/设置元素高度的最可靠方法是什么。

任何关于如何实施该特定指令的指南也将受到高度赞赏。

我需要构建这样的东西https://github.com/jedfoster/Readmore.js

解决方案：

在 Andzhik 的帮助下，我能够构建满足我要求的以下组件。

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;
        }
    }
}

用法：

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

如果有任何改进，请随时提出建议。

Answer 1

我制作了一个使用字符长度而不是 div 大小的版本。

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();       
    }
}

用法：

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

Answer 2

我认为您需要Component 而不是Directive。 Components 更有意义，因为您需要添加 Read more 按钮/链接，即更新 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;
}

用法：

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