ElementRef:
In Angular2 Doc, it suggest to "avoid" using ElementRef. It access DOM directly, can easily be attacked.
import {Component, OnInit, ViewChild, Renderer, ElementRef} from '@angular/core';
@Component({
moduleId: module.id,
selector: 'widget-three',
template: `<input type="text" #inputRef/>`
})
export class WidgetThree {
constructor(private elm: ElementRef) {
console.log("elm:", this.elm)
}
}
If we log out the ElementRef, we can see, it refer to host element.
Renderer:
In the doc, it also suggest, if you want to change some dom prop, use Renderer instead. ElementRef can be just a reference to access native element object.
import { Directive, ElementRef, Input, Renderer } from '@angular/core';
@Directive({ selector: '[myHighlight]' })
export class HighlightDirective {
constructor(el: ElementRef, renderer: Renderer) {
renderer.setElementStyle(el.nativeElement, 'backgroundColor', 'yellow');
}
}
This will set the host element background as yellow.
@ViewChild():
Access Child element by Ref or Class Object.
import {Component, OnInit, ViewChild, Renderer} from '@angular/core';
@Component({
moduleId: module.id,
selector: 'widget-three',
template: `<input type="text" #inputRef/>`
})
export class WidgetThree {
@ViewChild('inputRef') input;
constructor(private renderer: Renderer) {
}
ngAfterViewInit(){
this.renderer.invokeElementMethod(
this.input.nativeElement,
'focus',
[]
);
}
}
Here we have a ref "inputRef", we use ref to access input element.
'invokeElementMethod' will call the 'focus' method the the input nativeElement which should be:
this.input.nativeElement.focus()
But the risk is on mobile it might have different method to focus on input, 'invokeElementMethod' can safely help us to call the method .