How to get width of (DOM) Element in Angular2

问题:

there a some similiar threads but I couldn't find a suitable answer for my needs. So that direct DOM access should be strictly avoided in angular2 I'm just wondering whats best practice for this.

What I wan't to achieve is a resize of a element based on the current width.

workitemresize.component.ts

import { Directive, ElementRef, HostListener, Renderer, Input } from '@angular/core';

@Directive({
  selector: '[workItemResize]'
})

export class WorkItemResizeDirective implements ngAfterViewInit {

  private el: HTMLElement;
  private renderer: Renderer;

  constructor(el: ElementRef, public renderer: Renderer)
  { 
    this.el = el.nativeElement; 
    this.renderer = renderer;
  }  


  @HostListener('window:resize', ['$event.target']) 
  onResize() 
  { 
    this.resizeWorks();
  }

  ngAfterViewInit() {
    this.resizeWorks();
  }

  private resizeWorks(): void {
    this.renderer.setElementStyle(this.el, 'height', this.el.width); // <-- doesn't work I kow that this.el.width doesn't exist but just for demonstration purpose
    this.renderer.setElementStyle(this.el, 'height', '500'); // <-- works
  }

}

projects.template.html

<div class="posts row">
        <div class="work-item col-xs-12 col-sm-6 col-no-padding"  workItemResize *ngFor="let post of posts">

                <!-- show some fancy image -->
                <div class="img"  [ngStyle]="{'background-image':'url('+post.better_featured_image.source_url+')'}"></div>

        </div>
</div>

Related: https://github.com/angular/angular/issues/6515

回答1:

I don't know a way to get the width from the host element without accessing nativeElement but setting could be done like:

@HostListener('window:resize', ['$event.target']) 
onResize() { 
  this.resizeWorks();
}

@HostBinding('style.height.px')
elHeight:number;

private resizeWorks(): void {
  this.elHeight = this.el.nativeElement.width;
}

If you can add an element inside your components template like

<div style="width: 100%;" #div (window:resize)="elHeight = div.getBoundingClientRect()">
  <!-- your template here -->
</div>

then this would work without direct DOM access at all (but not after init).

回答2:

I tried out @GünterZöchbauer solution and refined it. You do not need HostListener to get bounds of div. Like with 'click' or other event (event)="function()", it will fire this function. I hope someone will find this helpful.

<div #div (window:resize)="onResize(div.getBoundingClientRect())">
   <!-- your template here -->
</div>


onResize() { 
   this.resizeWorks();
}

@HostBinding('style.height.px') elHeight:number;

private resizeWorks(): void {
   this.elHeight = this.el.nativeElement.width;
}

(#div) - this is variable needed to get measurement target. It does not have to be same name as element, it can be any name.

One more way to get element dimensions is to use ElementRef class from Angular Core, but then you have to find that child element which has width and height properties. I used this in Angular 2 Maps to get container width and height, but i found out that, using this method i had to find in element tree element which had these properties and it was second child of root element. It is more messy. ElementDimensions - is just a class with height and width which I made to contain those properties.

<div (window:resize)="onResize()">
   <!-- your template here -->
</div>

private getContainerDimensions(): ElementDimensions{
    var rootElement = this.elementRef.nativeElement;
    var childElement = rootElement.firstElementChild;
    var contentElement =  childElement.firstElementChild;

    return {
        height:contentElement.clientHeight,
        width: contentElement.clientWidth
    };
}

回答3:

I tested this way and simply worked! It seems that binding did this job.

<div #foto [style.height.px]="foto.getBoundingClientRect().width / 2">

回答4:

You can get the width of the component itself if that one has a display property defined (such as 'block' in the example below). Note that you should be able to define this style (using dom shadowing):

:host {
    display:block;
}

If you are not using dom shadowing (Ionic 2-3):

my-component {
    display:block;
}

Here is the controller (exposing the width as an observable):

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

@Component({
    selector: 'my-component',
    template: '{{$width|async}}',
    style: 'my-component {display: block;}'
})
export class MyComponent implements AfterViewInit {
    @Input() public gridWidth: number;
    private $width: Subject<number> = new Subject();

    constructor(private elementRef: ElementRef) {
    }

    public ngAfterViewInit(): void {
        this.emitWidth();
    }

    @HostListener('window:resize', ['$event.target'])
    public onResize(): void {
        this.emitWidth();
    }

    private emitWidth(): void {
        this.$width.next(this.getWidth());
    }

    private getWidth(): number {
        return this.getNativeElement().clientWidth;
    }

    private getNativeElement(): HTMLElement {
        return this.elementRef.nativeElement;
    }
}