ViewContainerRef 动态创建视图

Angular DOM 操作

相关的APIs和类：

• 查询DOM节点
  • template variable ref: 模版变量引用，相当于react中的ref
  • ViewChild: 查询DOM,返回单个元素引用
  • ViewChildren: 返回一个QueryList对象，包含一系列元素
• ElementRef: 元素引用
  • 查询的方式获取，比如 @ViewChild(‘myInput‘) inputElm: ElementRef
  • 依赖注入的方式，获取宿主元素，比如 constructor(private elem: ElementRef){}
• TemplateRef: 模板引用
  • 查询的方式， 比如 <ng-template #tpl></ng-template>
• ViewContainerRef: 视图容器，包含创建angular视图的方法和操作视图的apis
• ViewRef: 视图引用，angular最小的UI单元，创建的视图的返回类型就是ViewRef
• angular中的2种类型的视图
  • 插入式视图Embedded Views
  • 宿主视图 component instance views,即组件实例视图
• EmbeddedViewRef: 插入式视图引用，上面创建插入式视图防护的类型
• ComponentRef<C>: 组件视图引用，创建hostView时返回的类型 <C> 表示组件名

 https://upload-images.jianshu.io/upload_images/1203223-b115a5ab14bdbb05.png

Angular+DOM操作.png

示例

创建视图并插入

import {
  Component,
  ViewChild,
  TemplateRef,
  ViewContainerRef,
  ViewRef,
  AfterViewInit
} from ‘@angular/core‘;

@Component({
  selector: ‘app-sample‘,
  template: `
    <span>我是第一个span标签</span>
    <ng-container #vc></ng-container>
    <span>我是第二个span标签</span>
    <ng-template #tpl>
      <div>我是模版里面的div标签</div>
    </ng-template>
  `
})
export class SampleComponent implements AfterViewInit {
  // 查询元素， {read: ViewContainerRef} 不能省略，因为angular无法推断出它是一个容器
  @ViewChild(‘vc‘, {read: ViewContainerRef}) vc: ViewContainerRef;
  // {read: TemplateRef} 可以省略
  @ViewChild(‘tpl‘) tpl: TemplateRef<any>;

  constructor() {}

  ngAfterViewInit() {
    // 创建一个插入式视图， 一般插入式视图都对应的是模版视图
    const tplView: ViewRef = this.tpl.createEmbeddedView(null);

    // 插入到容器当中 使用视图容器操作视图的方法insert
    this.vc.insert(tplView);
    
  }
}

最后得到的结果是

<app-sample>
    <span>我是第一个span标签</span>
    <!--template bindings={}-->
    <div>我是模版里面的div标签</div>
    <span>我是第二个span标签</span>
    <!--template bindings={}-->
</app-sample>

可以看出 ng-container 和 ng-template 最后编译后都变为了注释

<!--template bindings={}-->

使用 ngTemplateOutlet 指令

angular为创建插入式视图提供了 ngTemplateOutlet 指令，这个和 router-outlet 功能类似，为模版提供了一个进入的入口，上面的例子可以改写为

import {
  Component,
} from ‘@angular/core‘;

@Component({
  selector: ‘app-sample‘,
  template: `
    <span>我是第一个span标签</span>
    <ng-container [ngTemplateOutlet]="tpl"></ng-container>
    <span>我是第二个span标签</span>
    <ng-template #tpl>
      <div>我是模版里面的div标签</div>
    </ng-template>
  `
})
export class SampleComponent {
}

可以看出这种十分的方便，在饿了吗angular tooltip组件中就使用到了这个指令

@Component({
  selector: ‘el-tooltip‘,
  template: `
    <div style="position: relative; display: inline-block;">
      <div [class]="‘el-tooltip__popper is-‘ + effect + ‘ ‘ + popperClass"
        style="left: -20000px; top: 0; position: absolute;"
        [@fadeAnimation]="!showPopper" [attr.x-placement]="xPlacement" #popperContent>
        <div x-arrow class="popper__arrow" [hidden]="!visibleArrow"></div>
        <ng-template [ngTemplateOutlet]="tip"></ng-template>  # 此处使用到了ngTemplateOutlet指令
      </div>
      <ng-content></ng-content>
    </div>
  `,
  animations: [fadeAnimation],
})
export class ElTooltip implements AfterContentInit {
  @ContentChild(‘tip‘) tip: TemplateRef<any>
}

使用时：

<el-tooltip>
  <ng-template #tip>我是将要插入的模版内容<ng-template>
</el-tooltip>

ngComponentOutlet

这个指令和上面的 ngTemplateOutlet类似，但是它将创建一个 host view(组件的实例)，而不是插入式视图，使用方式

<ng-container *ngComponentOutlet="ColorComponent"></ng-container>

ViewContainerRef源码

import { Injector } from ‘../di/injector‘;
import { ComponentFactory, ComponentRef } from ‘./component_factory‘;
import { ElementRef } from ‘./element_ref‘;
import { NgModuleRef } from ‘./ng_module_factory‘;
import { TemplateRef } from ‘./template_ref‘;
import { EmbeddedViewRef, ViewRef } from ‘./view_ref‘;
/**
 * Represents a container where one or more Views can be attached.
 * 表示能够被一个或者多个视图附着的容器
 * The container can contain two kinds of Views. Host Views, created by instantiating a
 * {@link Component} via {@link #createComponent}, and Embedded Views, created by instantiating an
 * {@link TemplateRef Embedded Template} via {@link #createEmbeddedView}.
 * 容器能够包含2种类型的视图： 宿主视图(组件实例) 和 插入式视图(使用模版创建的视图)
 * The location of the View Container within the containing View is specified by the Anchor
 * `element`. Each View Container can have only one Anchor Element and each Anchor Element can only
 * have a single View Container.
 *
 * Root elements of Views attached to this container become siblings of the Anchor Element in
 * the Rendered View.
 * 插入的视图的根元素会成为视图容器的兄弟节点，而不是之间插入到容器中，这点和router-outlet插入组件的方式一致
 *
 * To access a `ViewContainerRef` of an Element, you can either place a {@link Directive} injected
 * with `ViewContainerRef` on the Element, or you obtain it via a {@link ViewChild} query.
 * 可以通过注入的方式范围viewContainerRef 和 通过 ViewChild 查询的方式获取viewContainerRef
 * @stable
 */
export declare abstract class ViewContainerRef {
    /**
     * Anchor element that specifies the location of this container in the containing View.
     * <!-- TODO: rename to anchorElement -->
     */
    readonly abstract element: ElementRef; 
    readonly abstract injector: Injector;         // 注入器， 用于动态创建组件中
    readonly abstract parentInjector: Injector;   // 父注入器， 如果组件自身没有提供注入器，使用父注入器
    /**
     * Destroys all Views in this container. 销毁容器内的所有视图
     */
    abstract clear(): void;
    /**
     * Returns the {@link ViewRef} for the View located in this container at the specified index.
     * 返回视图引用索引
     */
    abstract get(index: number): ViewRef | null;

    /**
     *  获取视图容器的数量
     * Returns the number of Views currently attached to this container.
     */
    readonly abstract length: number;

    /**
     * 实例化一个插入式视图，可以插入到指定的索引位置，如果不指定索引，将放到最后面
     * Instantiates an Embedded View based on the {@link TemplateRef `templateRef`} and inserts it
     * into this container at the specified `index`.
     * 
     * If `index` is not specified, the new View will be inserted as the last View in the container.
     *
     * Returns the {@link ViewRef} for the newly created View. 返回一个视图引用
     */
    abstract createEmbeddedView<C>(templateRef: TemplateRef<C>, context?: C, index?: number): EmbeddedViewRef<C>;

    /**
     * 实例化单个组件，插入到宿主视图中，可以插入到指定的索引位置，如果不指定索引，将放到最后面
     * Instantiates a single {@link Component} and inserts its Host View into this container at the
     * specified `index`.
     * 
     * The component is instantiated using its {@link ComponentFactory} which can be
     * obtained via {@link ComponentFactoryResolver#resolveComponentFactory}.
     * 组件通过 ComponentFactory 实例化， 而组件工厂可以通过 ComponentFactoryResolver来创建
     * If `index` is not specified, the new View will be inserted as the last View in the container.
     *
     * You can optionally specify the {@link Injector} that will be used as parent for the Component.
     *
     * Returns the {@link ComponentRef} of the Host View created for the newly instantiated Component.
     */
    abstract createComponent<C>(componentFactory: ComponentFactory<C>, index?: number, injector?: Injector, projectableNodes?: any[][], ngModule?: NgModuleRef<any>): ComponentRef<C>;

    /**
     * 插入视图
     * Inserts a View identified by a {@link ViewRef} into the container at the specified `index`.
     * 
     * If `index` is not specified, the new View will be inserted as the last View in the container.
     *
     * Returns the inserted {@link ViewRef}.
     */
    abstract insert(viewRef: ViewRef, index?: number): ViewRef;

    /**
     * 依据索引移动视图
     * Moves a View identified by a {@link ViewRef} into the container at the specified `index`.
     *
     * Returns the inserted {@link ViewRef}.
     */
    abstract move(viewRef: ViewRef, currentIndex: number): ViewRef;

    /**
     * 返回视图的索引位置
     * Returns the index of the View, specified via {@link ViewRef}, within the current container or
     * `-1` if this container doesn‘t contain the View.
     */
    abstract indexOf(viewRef: ViewRef): number;

    /**
     * 移除视图
     * Destroys a View attached to this container at the specified `index`.
     *
     * If `index` is not specified, the last View in the container will be removed.
     */
    abstract remove(index?: number): void;

    /**
     * 将视图从当前容器中分离
     * Use along with {@link #insert} to move a View within the current container.
     *
     * If the `index` param is omitted, the last {@link ViewRef} is detached.
     */
    abstract detach(index?: number): ViewRef | null;
}

2种视图

模版视图

也称之为插入式视图

<ng-template #tpl></ng-template>
<ng-container #vc><ng-container>

class SampleComponent implments AfterViewInit {
  @ViewChild(‘tpl‘) tpl: Template<any>;
  @ViewChild(‘vc‘, {read: ViewContainerRef}) vc: ViewContainerRef;
  ngAfterViewInit() {
    let embeddedView: ViewRef = this.tpl.createEmbeddedView(null);
    this.vc.insert(embeddedView);
  }
}

宿主视图

和组件相关

<ng-container #vc><ng-container>

class SampleComponent implments AfterViewInit {
  @ViewChild(‘tpl‘) tpl: Template<any>;
  @ViewChild(‘vc‘, {read: ViewContainerRef}) vc: ViewContainerRef;
  componentRef: ComponentRef<ColorComponent>;

  constructor(private injector: Injector, provate cfr: ComponentFactoryResolver) {}
  ngAfterViewInit() {
    const factory = this.cfr.rosolveComponentFactory(ColorComponent); // 创建组件工厂
    this.componentRef = this.vc.createComponent(factory); // 创建组件引用
    // this.componentRef = factory.create(this.injector); // 创建注入器
    // let view: ViewRef = componentRef.hostView;     // 创建宿主视图
    // this.vc.insert(view);
  }
}

最后动态创建的组件需要添加到 entryComponent 中

示例：

• angular-hostView-example

文章参考：

• Exploring Angular DOM manipulation techniques using ViewContainerRef