Angular development practice (7): Cross-platform operation of DOM and renderer Renderer2

In "Angular Development Practice (6): Server-side Rendering"At the end of this article, we also mentioned several events that need to be kept in mind in Server-side rendering, These include not using browser-specific types such as window, document, navigator and directly manipulating DOM elements.

This brings us to one of Angular’s ​​main features: across all platforms. With the right approach, applications built using Angular can be reused on multiple different platforms - web, mobile web, mobile apps, native apps, and desktop native apps.

In order to support cross-platform, Angular encapsulates the differences of different platforms through abstraction layers. For example, abstract class Renderer2, abstract class RootRenderer, etc. are defined. In addition, the following reference types are defined: ElementRef, TemplateRef, ViewRef, ComponentRef, ViewContainerRef, etc. Obtain DOM elements through template variables, @ViewChild and other methods.

For demonstration, first define a component DemoComponent:

import { AfterViewInit, Component, ElementRef, Renderer2, ViewChild } from '@angular/core';

@Component({
    template: `
        <p id="demop" #demop>this is p!</p>
        p的id：{{demop.id}} <!-- p的id：demop -->
    `
})
export class DemoComponent implements AfterViewInit {
    @ViewChild(&#39;demop&#39;) demop: ElementRef; // @ViewChild通过模板变量名获取

    constructor(private renderer: Renderer2) {
    }

    ngAfterViewInit() {
        console.log(&#39;p的id：&#39; + this.demop.nativeElement.id); // p的id：demop
        this.renderer.setStyle(this.demop.nativeElement, &#39;background-color&#39;, &#39;red&#39;); // 通过Renderer2设置p的css样式background-color
    }
}

Get the p in the component

In Angular applications, DOM elements should not be obtained directly through native API or jQuery:

let element1 = document.getElementById("demop"); // jQuery获取: $('#demop')

Instead, you should get the DOM element through the method provided by Angular:

Template variable

<p id="demop" #demop>this is p!</p>
p的id：{{demop.id}} <!-- p的id：demop -->

In the component template, we define the template of #demop on p variable, then demop is equal to the DOM object of p, so we can directly obtain the id of p through demop.id.

@ViewChild

@ViewChild('demop') demop: ElementRef; // @ViewChild通过模板变量名获取

ngAfterViewInit() {
    console.log('p的id：' + this.demop.nativeElement.id); // p的id：demop
}

In the component class, we obtain the ElementRef object that wraps the DOM object of p through @ViewChild. The ElementRef is defined as follows:

class ElementRef<T> {
  constructor(nativeElement: T)
  nativeElement: T
}

So we can Get the DOM object of p through this.demop.nativeElement in ngAfterViewInit, and then get the id of the element.

p in the operation component

has obtained the DOM object of p through several methods above, so how do we operate on it (setting styles, attributes, inserting sub-elements, etc.) ? Via raw API or jQuery is definitely not allowed.

In this way, we introduce the Angular abstract class Renderer2 to set styles, attributes, insert sub-elements and other operations on elements.

Renderer2 is defined as follows:

class Renderer2 {
    get data: {...}
    destroyNode: ((node: any) => void) | null
    destroy(): void
    createElement(name: string, namespace?: string | null): any // 创建元素
    createComment(value: string): any // 创建注释元素
    createText(value: string): any // 创建文本元素
    appendChild(parent: any, newChild: any): void // 添加子元素（在最后）
    insertBefore(parent: any, newChild: any, refChild: any): void // 添加子元素（在最前）
    removeChild(parent: any, oldChild: any): void // 移除子元素
    selectRootElement(selectorOrNode: string | any): any // 获取根元素
    parentNode(node: any): any // 获取父元素
    nextSibling(node: any): any // 获取下一个兄弟元素
    setAttribute(el: any, name: string, value: string, namespace?: string | null): void // 设置属性
    removeAttribute(el: any, name: string, namespace?: string | null): void // 移除属性
    addClass(el: any, name: string): void // 添加样式类
    removeClass(el: any, name: string): void // 移除样式类
    setStyle(el: any, style: string, value: any, flags?: RendererStyleFlags2): void // 设置样式
    removeStyle(el: any, style: string, flags?: RendererStyleFlags2): void // 移除样式
    setProperty(el: any, name: string, value: any): void // 设置DOM对象属性，不同于元素属性
    setValue(node: any, value: string): void // 设置元素值
    listen(target: 'window' | 'document' | 'body' | any, eventName: string, callback: (event: any) => boolean | void): () => void // 注册事件
}

Therefore, if we want to change the background color of p, we can do this:

ngAfterViewInit() {
    this.renderer.setStyle(this.demop.nativeElement, 'background-color', 'red'); // 通过Renderer2设置p的css样式background-color
}

                                                 

At the end of the article "Angular Development Practice (6): Server-side Rendering", we also mentioned the need for Server-side rendering A few things to keep in mind include not using browser-specific types such as window, document, navigator, and directly manipulating DOM elements.

This brings us to one of Angular’s ​​main features: across all platforms. With the right approach, applications built using Angular can be reused on multiple different platforms - web, mobile web, mobile apps, native apps, and desktop native apps.

In order to support cross-platform, Angular encapsulates the differences of different platforms through abstraction layers. For example, abstract class Renderer2, abstract class RootRenderer, etc. are defined. In addition, the following reference types are defined: ElementRef, TemplateRef, ViewRef, ComponentRef, ViewContainerRef, etc. Obtain DOM elements through template variables, @ViewChild and other methods.

For demonstration, first define a component DemoComponent:

import { AfterViewInit, Component, ElementRef, Renderer2, ViewChild } from '@angular/core';

@Component({
    template: `
        <p id="demop" #demop>this is p!</p>
        p的id：{{demop.id}} <!-- p的id：demop -->
    `
})
export class DemoComponent implements AfterViewInit {
    @ViewChild(&#39;demop&#39;) demop: ElementRef; // @ViewChild通过模板变量名获取

    constructor(private renderer: Renderer2) {
    }

    ngAfterViewInit() {
        console.log(&#39;p的id：&#39; + this.demop.nativeElement.id); // p的id：demop
        this.renderer.setStyle(this.demop.nativeElement, &#39;background-color&#39;, &#39;red&#39;); // 通过Renderer2设置p的css样式background-color
    }
}

Get the p in the component

In Angular applications, DOM elements should not be obtained directly through native API or jQuery:

let element1 = document.getElementById("demop"); // jQuery获取: $('#demop')

Instead, you should get the DOM element through the method provided by Angular:

Template variable

<p id="demop" #demop>this is p!</p>
p的id：{{demop.id}} <!-- p的id：demop -->

In the component template, we define the template of #demop on p variable, then demop is equal to the DOM object of p, so we can directly obtain the id of p through demop.id.

@ViewChild

@ViewChild('demop') demop: ElementRef; // @ViewChild通过模板变量名获取

ngAfterViewInit() {
    console.log('p的id：' + this.demop.nativeElement.id); // p的id：demop
}

In the component class, we obtain the ElementRef object that wraps the DOM object of p through @ViewChild. The ElementRef is defined as follows:

class ElementRef<T> {
  constructor(nativeElement: T)
  nativeElement: T
}

So we can Get the DOM object of p through this.demop.nativeElement in ngAfterViewInit, and then get the id of the element.

p in the operation component

has obtained the DOM object of p through several methods above, so how do we operate on it (setting styles, attributes, inserting sub-elements, etc.) ? Via raw API or jQuery is definitely not allowed.

In this way, we introduce the Angular abstract class Renderer2 to set styles, attributes, insert sub-elements and other operations on elements.

Renderer2 is defined as follows:

class Renderer2 {
    get data: {...}
    destroyNode: ((node: any) => void) | null
    destroy(): void
    createElement(name: string, namespace?: string | null): any // 创建元素
    createComment(value: string): any // 创建注释元素
    createText(value: string): any // 创建文本元素
    appendChild(parent: any, newChild: any): void // 添加子元素（在最后）
    insertBefore(parent: any, newChild: any, refChild: any): void // 添加子元素（在最前）
    removeChild(parent: any, oldChild: any): void // 移除子元素
    selectRootElement(selectorOrNode: string | any): any // 获取根元素
    parentNode(node: any): any // 获取父元素
    nextSibling(node: any): any // 获取下一个兄弟元素
    setAttribute(el: any, name: string, value: string, namespace?: string | null): void // 设置属性
    removeAttribute(el: any, name: string, namespace?: string | null): void // 移除属性
    addClass(el: any, name: string): void // 添加样式类
    removeClass(el: any, name: string): void // 移除样式类
    setStyle(el: any, style: string, value: any, flags?: RendererStyleFlags2): void // 设置样式
    removeStyle(el: any, style: string, flags?: RendererStyleFlags2): void // 移除样式
    setProperty(el: any, name: string, value: any): void // 设置DOM对象属性，不同于元素属性
    setValue(node: any, value: string): void // 设置元素值
    listen(target: 'window' | 'document' | 'body' | any, eventName: string, callback: (event: any) => boolean | void): () => void // 注册事件
}

Therefore, if we want to change the background color of p, we can do this:

ngAfterViewInit() {
    this.renderer.setStyle(this.demop.nativeElement, 'background-color', 'red'); // 通过Renderer2设置p的css样式background-color
}

Related Recommended:

Angular Development Practice (5): In-depth Analysis of Change Monitoring

Angular Development Practice (6): Server-side Rendering

Angular Development Practice (1): Environment Preparation and Framework Construction

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